The dynamic responses and generated voltage in a curved sandwich beam with glass reinforced laminate(GRL)layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact(LVI)are investigate...The dynamic responses and generated voltage in a curved sandwich beam with glass reinforced laminate(GRL)layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact(LVI)are investigated.The current study aims to carry out a dynamic analysis on the sandwich beam when the impactor hits the top face sheet with an initial velocity.For the layer analysis,the high-order shear deformation theory(HSDT)and Frostig's second model for the displacement fields of the core layer are used.The classical non-adhesive elastic contact theory and Hunter's principle are used to calculate the dynamic responses in terms of time.In order to validate the analytical method,the outcomes of the current investigation are compared with those gained by the experimental tests carried out by other researchers for a rectangular composite plate subject to the LVI.Finite element(FE)simulations are conducted by means of the ABAQUS software.The effects of the parameters such as foam modulus,layer material,fiber angle,impactor mass,and its velocity on the generated voltage are reviewed.展开更多
To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire m...To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.展开更多
In order to effectively describe the progressively intralaminar and interlam- inar damage for composite laminates, a three dimensional progressive damage model for composite laminates to be used for low-velocity impac...In order to effectively describe the progressively intralaminar and interlam- inar damage for composite laminates, a three dimensional progressive damage model for composite laminates to be used for low-velocity impact is presented. Being applied to three-dimensional (3D) solid elements and cohesive elements, the nonlinear damage model can be used to analyze the dynamic performance of composite structure and its failure be- havior. For the intralaminar damage, as a function of the energy release rate, the damage model in an exponential function can describe progressive development of the damage. For the interlaminar damage, the damage evolution is described by the framework of the continuum mechanics through cohesive elements. Coding the user subroutine VUMAT of the finite element software ABAQUS/Explicit, the model is applied to an example, i.e., carbon fiber reinforced epoxy composite laminates under low-velocity impact. It is shown that the prediction of damage and deformation agrees well with the experimental results.展开更多
A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity ...A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.展开更多
Improvement from the pseudo-elastic effect of shape memory alloy (SMA) on the low-velocity impact (LVI) resistance of a composite plate is investigated by the finite element method (FEM). The stiffness matrix of...Improvement from the pseudo-elastic effect of shape memory alloy (SMA) on the low-velocity impact (LVI) resistance of a composite plate is investigated by the finite element method (FEM). The stiffness matrix of the dynamic finite element equation is established step by step and the martensite fraction is obtained at each time step. The direct Newmark integration method is employed in solving the dynamic finite element equation, while the impact contact force is determined using the modified Hertz's law. It is found that SMA can effectively improve the performance of a composite structure subjected to low-velocity impact. Numerical results show that the deflection of a SMA-hybrid composite plate has been reduced approximately by thirty percent when the volume fraction of the embedded SMA reaches 0.3.展开更多
A method to improve the low-velocity impact performance of composite laminate is proposed, and a multi-island genetic algorithm is used for the optimization of composite laminate stacking sequence under low-velocity i...A method to improve the low-velocity impact performance of composite laminate is proposed, and a multi-island genetic algorithm is used for the optimization of composite laminate stacking sequence under low-velocity impact loads based on a 2D dynamic impact finite element analysis. Low-velocity impact tests and compression-after impact(CAI) tests have been conducted to verify the effectiveness of optimization method. Experimental results show that the impact damage areas of the optimized laminate have been reduced by 42.1% compared to the baseline specimen, and the residual compression strength has been increased by 10.79%, from baseline specimen 156.97 MPa to optimized 173.91 MPa. The tests result shows that optimization method can effectively enhance the impact performances of the laminate.展开更多
This paper deals with the collision of sphere shape grenades with sand media.The central issue of the article is the establishing of an empirical velocity equation of the grenade while impacting on sand that is used t...This paper deals with the collision of sphere shape grenades with sand media.The central issue of the article is the establishing of an empirical velocity equation of the grenade while impacting on sand that is used to solve motion equations of the mechanical mechanism inside the impact grenade fuze.The paper focuses on impact velocities that are lower than 5 m s^(-1).An experiment was conducted to study the velocity of the grenade while impacting on dry sand.A high-speed camera video was used to capture the grenade positions.The grenade velocity in the impact process was generated from these video data.Some types of fitting curves are used to regress the velocity equation of the grenade while interacting with the sand media and the best-fitting model is chosen.The result shows the regression curve has a high correlation with the experiment data for grenade velocities below 5 m s^(-1).The received regression equation is useful for analyzing the working ability of the inertial mechanism inside the impact grenade or analyzing and choosing the appropriate parameters of each part in the inertial mechanism to meet the required characteristics of the mechanism.展开更多
Since composite sandwich structures are susceptible to low-velocity impact damage,a thorough characterization of the loading and damage process during impact is important.In the present paper,the low-velocity impact r...Since composite sandwich structures are susceptible to low-velocity impact damage,a thorough characterization of the loading and damage process during impact is important.In the present paper,the low-velocity impact response of carbon fiber composites lattice structures is investigated by experimental and numerical methods.Impact tests on composite plates are performed using an instrumented drop-weight machine(Instron 9250HV)and a new damage mode is observed.A three-dimensional finite element model is built by ABAQUS/Explicit and user subroutine(VUMAT)to predict the peak loading and simulate the complicated damage problem.The numerical predictions are in good agreement with the experimental results.展开更多
Through theoretical analysis and finite element simulation,the low-velocity impact of rectangular foam-filled fiber metal laminate(FML)tubes is studied in this paper.According to the rigid-plastic material approximati...Through theoretical analysis and finite element simulation,the low-velocity impact of rectangular foam-filled fiber metal laminate(FML)tubes is studied in this paper.According to the rigid-plastic material approximation with modifications,simple analytical solutions are obtained for the dynamic response of rectangular foam-filled FML tubes.The numerical calculations for low-velocity impact of rectangular foam-filled FML tubes are conducted.The accuracy of analytical solutions and numerical results is verified by each other.Finally,the effects of the metal volume fraction of FMLs,the number of the metal layers in FMLs,and the foam strength on the dynamic response of foam-filled tubes are discussed through the analytical model in details.It is shown that the force increases with the increase in the metal volume fraction in FMLs,the number of the metal layers in FML,and the foam strength for the given deflection.展开更多
Low-velocity impact and in-plane axial compression after impact(CAI)behaviors of carbon-aramid/epoxy hybrid braided composite laminates were investigated experimentally.The following three different types of carbon-ar...Low-velocity impact and in-plane axial compression after impact(CAI)behaviors of carbon-aramid/epoxy hybrid braided composite laminates were investigated experimentally.The following three different types of carbon-aramid/epoxy hybrid braided composite laminates were produced and tested:(a)inter-hybrid laminates,(b)sandwich-like inter-hybrid laminates,and(c)unsymmetric-hybrid laminates.At the same time,carbon/epoxy braided composite laminates were used for comparisons.Impact properties and impact resistance were studied.Internal damages and damage mechanisms of laminates were detected by ultrasonic C-scan and B-scan methods.The results show that the ductility index(DI)values of three kinds of hybrid laminates aforementioned are 37%,4%and 120%higher than those of carbon/epoxy laminates,respectively.The peak load of inter-hybrid laminates is higher than that of sandwich-like inter-hybrid laminates and unsymmetric-hybrid laminates.The average damage area and dent depths of inter-hybrid laminates are 64%and 69%smaller than those of carbon/epoxy laminates.Those results show that carbon-aramid/epoxy hybrid braided composite laminates could significantly improve the impact properties and toughness of non-hybrid braided composite laminates.展开更多
Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistanc...Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistance of foam sandwich composites,an innovative concept of a stitched multi-layer sandwich structure by organically combining the discrete splitting of foam layer with full thickness stitching was proposed,and its low-velocity impact resistance obtained through drop-hammer impact tests was explored.The results showed that the multi-layer foam sandwich structure acted as a stress disperser and reduced the irreversible impact damage.The depth and area of low-velocity impact damage of multi-layer foam sandwich composites gradually decreased with increasing the number of the layers.The stitched structure would improve the integrity of the foam sandwich composites and inhibit the propagation of cracks.The maximum impact load of the stitched foam sandwich composite increased by approximately 5% compared with that of the non-stitched material.In addition,the low-velocity impact damage depth,damage area and absorbed energy of the stitched three-layer foam sandwich composite were reduced by 37.7%,34.6% and 20.7%,respectively,compared with those of the non-stitched single-layer sandwich material.展开更多
The mechanical properties of Ti/APC-2/Kevlar/epoxy hybrid composite laminates after low velocity impact were investigated at room temperature. There were three types of samples, including three layered [Ti/(0/90)s/Ti]...The mechanical properties of Ti/APC-2/Kevlar/epoxy hybrid composite laminates after low velocity impact were investigated at room temperature. There were three types of samples, including three layered [Ti/(0/90)s/Ti], five layered [Ti/(0/90)2/]s and nine layered [Ti/Kevlar/Ti/(0/90)2/]s. The lay-ups of APC-2 were crossply, while Ti layers were treated by chromic acid anodic method. Ti and APC-2 were stacked to fabricate the composite laminates via hot press curing process. Kevlar layers were added to fabricate nine-layered composite laminates via vacuum assisted resin transfer molding. The drop-weight tests were conducted with a hemispherical nosed projectile in 10 mm diameter. The impact loads were 5 kg and 10 kg and impact heights were adjusted to penetrate samples or the maximum height 1.50 m. The static tensile tests were conducted to measure the residual mechanical properties after impact. The free body drop tests were also simulated by using finite element method and software ANSYS LS-DYNA3D. The results showed that the bottom Ti layer absorbed more internal energy than the top Ti layer, then the cracks were found in the bottom Ti layer more often. The ultimate tensile strength reduced significantly after impact. The initial longitudinal compliance increased with the impact height increasing and decreased after the samples penetrated. Comparing the experimental data with the numerical results, it was found that the damage of the latter was more serious than that of the former. On the conservative side, the results of numerical simulation are acceptable and adopted for applications when no testing data available.展开更多
In recent years, the development and application of high performance fiber reinforced concrete or cementitious composites are increasing due to their high ductility and energy absorption characteristics. However, it i...In recent years, the development and application of high performance fiber reinforced concrete or cementitious composites are increasing due to their high ductility and energy absorption characteristics. However, it is difficult to obtain the required properties of the FRCC by simply adding fiber to the concrete matrix. Many researchers are paying attention to fiber reinforced polymers (FRP) for the reinforcement of construction structures because of their significant advantages over high strain rates. However, the actual FRP products are skill-dependent, and the quality may not be uniform. Therefore, in this study, two-way punching tests were carried out to evaluate the performances of FRP strengthened and steel and polyvinyl alcohol (PVA) fiber reinforced concrete specimens for impact and static loads. The FRP reinforced normal concrete (NC), steel fiber reinforced concrete (SFRC), and PVA FRCC specimens showed twice the amount of enhanced dissipated energy (total energy) under impact loadings than the non-retrofitted specimens. In the low-velocity impact test of the two-way NC specimens strengthened by FRPs, the total dissipated energy increased by 4 to 5 times greater than the plain NC series. For the two-way specimens, the total energy increased by 217% between the non-retrofitted SFRC and NC specimens. The total dissipated energy of the CFRP retrofitted SFRC was twice greater than that of the plain SFRC series. The PVA FRCC specimens showed 4 times greater dissipated energy than for the energy of the plain NC specimens. For the penetration of two-way specimens with fibers, the Hughes formula considering the tensile strength of concrete was a better predictor than other empirical formulae.展开更多
We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser ...We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis(pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 10^-8 to 1 × 10^-9 atoms/s, corresponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20(m/s)/rad and the mean sensitivity of flux of 1.2 × 10^-9(atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simulation method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux,which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.展开更多
The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation c...The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation characteristics of the glass fiber reinforced thermoplastic polypropylene and carbon fiber reinforced thermosetting epoxy resin laminates wildly used in the aircraft industry.The impact tests were conducted at five energy levels.Characterization parameters such as impact load,displacement,and absorbed energy were measured.The damage evolution and damage modes of the laminates were analyzed through active and passive thermography,ultrasonic C-scan,and optical microscope.The results indicate that Thermosets(TS)laminates exhibit better impact resistance,while Thermoplastics(TP)laminates show higher delamination ductility,and the maximum contact force of TP laminates is much smaller than that of the TS laminates under lowvelocity impacts,but the low bending stiffness and low ductility of the TP matrix cause the difference in energy absorption level between the two not significant.The temperature characteristic changes of passive infrared thermography heat maps could characterize the damage mode of the laminates.The correlation between the heat maps and the impact characteristic curves is explained;the fluctuation of the impact characteristic curves is directly related to the hot spot characteristics changes of the heat maps.More frequent curve fluctuations correspond to a larger and brighter hot spot on the heat map,which peaks at the maximum impact load after the impact force versus time curve fluctuation cutoff point,the maximum center displacement of the impact force versus displacement curve,and the maximum absorbed energy of the absorbed energy versus time curve.展开更多
This study details the low-velocity impact and compression-after-impact(CAI)behaviour of flax fibre-reinforced polymer(FFRP)composites.The impact resistance,energy absorption efficiency and residual compressive streng...This study details the low-velocity impact and compression-after-impact(CAI)behaviour of flax fibre-reinforced polymer(FFRP)composites.The impact resistance,energy absorption efficiency and residual compressive strength as well as the damage pattern of the FFRP composites are compared with the corresponding features of glass fibre-reinforced polymer(GFRP)composites,and the effect of the stacking sequence of FFRP composites is also investigated.The results show that the cross-ply FFRP composites have the highest impact resistance,whereas the multi-directional ply composites have the lowest impact resistance but the highest energy absorption efficiency.The energy absorption efficiency of the FFRP composites is greater than that of the GFRP composites,but the penetration resistance and residual compressive strength of the FFRP composites are lower than those of the GFRP composites with the same stacking sequence,mainly due to the lower tensile strength and elongation at fracture of the FFRP composites.It is also reported that the damage pattern of the FFRP composites is localised cracking and delamination,unlike the overall delamination failure exhibited in the GFRP composites after CAI testing.Finally,the failure mechanisms of the FFRP and GFRP composites are detailed.展开更多
A theoretical solution is aimed to be developed in this research for predicting the failure in internally pressurized composite pressure vessels exposed to low-velocity impact.Both in-plane and out-of-plane failure mo...A theoretical solution is aimed to be developed in this research for predicting the failure in internally pressurized composite pressure vessels exposed to low-velocity impact.Both in-plane and out-of-plane failure modes are taken into account simultaneously and thus all components of the stress and strain fields are derived.For this purpose,layer-wise theory is employed in a composite cylinder under internal pressure and low-velocity impact.Obtained stress/strain components are fed into appropriate failure criteria for investigating the occurrence of failure.In case of experiencing any in-plane failure mode,the evolution of damage is modeled using progressive damage modeling in the context of continuum damage mechanics.Namely,mechanical properties of failed ply are degraded and stress analysis is performed on the updated status of the model.In the event of delamination occurrence,the solution is terminated.The obtained results are validated with available experimental observations in open literature.It is observed that the sequence of in-plane failure and delamination varies by increasing the impact energy.展开更多
The Grid-Characteristic numerical Method(GCM)that is quite common in solving aero and hydrodynamic problems can also be applied for mechanics of solids.It allows to implement complex border and contact conditions,incl...The Grid-Characteristic numerical Method(GCM)that is quite common in solving aero and hydrodynamic problems can also be applied for mechanics of solids.It allows to implement complex border and contact conditions,including the non-reflecting border and the destructible contact.Both this conditions are very important for the precise and effective modeling of LowVelocity Impacts(LVI)on fiber and Fiber-Metal Laminates(FML)and the resulting Barely Visible Impact Damage(BVID)that influences the residual strength of a composite aircraft part.BVID is the type of damage that is not visible by the naked eye and can be hardly detected by a standard ultrasound equipment that is used for regular maintenance.It can appear during any weak impacts like bird strike or hail.Determining its influence on the residual strength of the part is very important to define the priorities of development of ultrasound diagnostics.In this paper,the GCM was applied for a full cycle of loading of an FML aircraft cover part.The FML consisted of a Carbon Fiber Reinforced Polymer(CFRP)and a single titanium layer on the upper surface.The cycle of loading in a single calculation consisted of an LVI caused by a small striker and a comparatively slow compressive in-plane loading.Three-dimensional patterns of velocity and stress distributions over the time of calculation are given.Destruction patterns,obtained via the Hashin failure criterion are given and analyzed.展开更多
文摘The dynamic responses and generated voltage in a curved sandwich beam with glass reinforced laminate(GRL)layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact(LVI)are investigated.The current study aims to carry out a dynamic analysis on the sandwich beam when the impactor hits the top face sheet with an initial velocity.For the layer analysis,the high-order shear deformation theory(HSDT)and Frostig's second model for the displacement fields of the core layer are used.The classical non-adhesive elastic contact theory and Hunter's principle are used to calculate the dynamic responses in terms of time.In order to validate the analytical method,the outcomes of the current investigation are compared with those gained by the experimental tests carried out by other researchers for a rectangular composite plate subject to the LVI.Finite element(FE)simulations are conducted by means of the ABAQUS software.The effects of the parameters such as foam modulus,layer material,fiber angle,impactor mass,and its velocity on the generated voltage are reviewed.
基金supported by the National Natural Science Foundation of China(grant number 51805086)the Natural Science Foundation of Fujian Province,China(grant number 2018J01763)。
文摘To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.
基金supported by the National Natural Science Foundation of China(No.11072202)
文摘In order to effectively describe the progressively intralaminar and interlam- inar damage for composite laminates, a three dimensional progressive damage model for composite laminates to be used for low-velocity impact is presented. Being applied to three-dimensional (3D) solid elements and cohesive elements, the nonlinear damage model can be used to analyze the dynamic performance of composite structure and its failure be- havior. For the intralaminar damage, as a function of the energy release rate, the damage model in an exponential function can describe progressive development of the damage. For the interlaminar damage, the damage evolution is described by the framework of the continuum mechanics through cohesive elements. Coding the user subroutine VUMAT of the finite element software ABAQUS/Explicit, the model is applied to an example, i.e., carbon fiber reinforced epoxy composite laminates under low-velocity impact. It is shown that the prediction of damage and deformation agrees well with the experimental results.
基金Funded by the Fundamental Research Funds for the Central Universities(No.2018IB001)and the National High-tech Research and Development Program of China(863 Program)(No.2013AA031306)。
文摘A combination of experimental measurements and numerical analysis was utilized to study the low-velocity impact damage of domestic carbon fiber-reinforced composites(CFRCs).The results indicated that the low-velocity impact damage induced pits and longitudinal cracks on the front side,oblique cracks and delaminationin on the back side.The pit depth increased with the increasing impact energy.It was demonstrated that the numerical analysis strain history curve was similar to the experimentally measured strain history curve,which verified the accuracy of numerical analysis in which the Hashin failure criterion was used.The work provides basic data and theoretical basis for the promotion and application of the domestic carbon fiber,and demonstrates the feasibility of replacing imported carbon fibers with domestic carbon fibers.
基金Project supported by the Key Project for Science and Technology Study of Ministry of Education of China (No.00085).
文摘Improvement from the pseudo-elastic effect of shape memory alloy (SMA) on the low-velocity impact (LVI) resistance of a composite plate is investigated by the finite element method (FEM). The stiffness matrix of the dynamic finite element equation is established step by step and the martensite fraction is obtained at each time step. The direct Newmark integration method is employed in solving the dynamic finite element equation, while the impact contact force is determined using the modified Hertz's law. It is found that SMA can effectively improve the performance of a composite structure subjected to low-velocity impact. Numerical results show that the deflection of a SMA-hybrid composite plate has been reduced approximately by thirty percent when the volume fraction of the embedded SMA reaches 0.3.
基金Funded by the National Natural Science Foundation of China(No.51275393)the Fundamental Research Funds for the Central Universities(No.xjj2017160)
文摘A method to improve the low-velocity impact performance of composite laminate is proposed, and a multi-island genetic algorithm is used for the optimization of composite laminate stacking sequence under low-velocity impact loads based on a 2D dynamic impact finite element analysis. Low-velocity impact tests and compression-after impact(CAI) tests have been conducted to verify the effectiveness of optimization method. Experimental results show that the impact damage areas of the optimized laminate have been reduced by 42.1% compared to the baseline specimen, and the residual compression strength has been increased by 10.79%, from baseline specimen 156.97 MPa to optimized 173.91 MPa. The tests result shows that optimization method can effectively enhance the impact performances of the laminate.
基金supported by the research project of the University of Defence in Brno DZRO-FVT22-VAROPS。
文摘This paper deals with the collision of sphere shape grenades with sand media.The central issue of the article is the establishing of an empirical velocity equation of the grenade while impacting on sand that is used to solve motion equations of the mechanical mechanism inside the impact grenade fuze.The paper focuses on impact velocities that are lower than 5 m s^(-1).An experiment was conducted to study the velocity of the grenade while impacting on dry sand.A high-speed camera video was used to capture the grenade positions.The grenade velocity in the impact process was generated from these video data.Some types of fitting curves are used to regress the velocity equation of the grenade while interacting with the sand media and the best-fitting model is chosen.The result shows the regression curve has a high correlation with the experiment data for grenade velocities below 5 m s^(-1).The received regression equation is useful for analyzing the working ability of the inertial mechanism inside the impact grenade or analyzing and choosing the appropriate parameters of each part in the inertial mechanism to meet the required characteristics of the mechanism.
基金Sponsored by the National Natural Science Foundation of China(Grant No.90816024and10872059)the Major State Basic Research Development Pro-gram of China(973 Program)(Grant No.2006CB601206)the Program of Excellent Team in Harbin Institute of Technology
文摘Since composite sandwich structures are susceptible to low-velocity impact damage,a thorough characterization of the loading and damage process during impact is important.In the present paper,the low-velocity impact response of carbon fiber composites lattice structures is investigated by experimental and numerical methods.Impact tests on composite plates are performed using an instrumented drop-weight machine(Instron 9250HV)and a new damage mode is observed.A three-dimensional finite element model is built by ABAQUS/Explicit and user subroutine(VUMAT)to predict the peak loading and simulate the complicated damage problem.The numerical predictions are in good agreement with the experimental results.
基金the National Natural Science Foundation of China(Nos.11872291 and11972281)the Jiangsu Key Laboratory of Engineering Mechanics,Southeast University+2 种基金the Fundamental Research Funds for the Central Universities(No.LEM21B01)the Key Laboratory of Impact and Safety Engineering(Ningbo University),Ministry of Education(No.cj202002)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2020JM-034)。
文摘Through theoretical analysis and finite element simulation,the low-velocity impact of rectangular foam-filled fiber metal laminate(FML)tubes is studied in this paper.According to the rigid-plastic material approximation with modifications,simple analytical solutions are obtained for the dynamic response of rectangular foam-filled FML tubes.The numerical calculations for low-velocity impact of rectangular foam-filled FML tubes are conducted.The accuracy of analytical solutions and numerical results is verified by each other.Finally,the effects of the metal volume fraction of FMLs,the number of the metal layers in FMLs,and the foam strength on the dynamic response of foam-filled tubes are discussed through the analytical model in details.It is shown that the force increases with the increase in the metal volume fraction in FMLs,the number of the metal layers in FML,and the foam strength for the given deflection.
基金National Natural Science Foundation of China(No.11102133)Tianjin National Natural Science Foundation,China(No.19JCYBJC18300)。
文摘Low-velocity impact and in-plane axial compression after impact(CAI)behaviors of carbon-aramid/epoxy hybrid braided composite laminates were investigated experimentally.The following three different types of carbon-aramid/epoxy hybrid braided composite laminates were produced and tested:(a)inter-hybrid laminates,(b)sandwich-like inter-hybrid laminates,and(c)unsymmetric-hybrid laminates.At the same time,carbon/epoxy braided composite laminates were used for comparisons.Impact properties and impact resistance were studied.Internal damages and damage mechanisms of laminates were detected by ultrasonic C-scan and B-scan methods.The results show that the ductility index(DI)values of three kinds of hybrid laminates aforementioned are 37%,4%and 120%higher than those of carbon/epoxy laminates,respectively.The peak load of inter-hybrid laminates is higher than that of sandwich-like inter-hybrid laminates and unsymmetric-hybrid laminates.The average damage area and dent depths of inter-hybrid laminates are 64%and 69%smaller than those of carbon/epoxy laminates.Those results show that carbon-aramid/epoxy hybrid braided composite laminates could significantly improve the impact properties and toughness of non-hybrid braided composite laminates.
文摘Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistance of foam sandwich composites,an innovative concept of a stitched multi-layer sandwich structure by organically combining the discrete splitting of foam layer with full thickness stitching was proposed,and its low-velocity impact resistance obtained through drop-hammer impact tests was explored.The results showed that the multi-layer foam sandwich structure acted as a stress disperser and reduced the irreversible impact damage.The depth and area of low-velocity impact damage of multi-layer foam sandwich composites gradually decreased with increasing the number of the layers.The stitched structure would improve the integrity of the foam sandwich composites and inhibit the propagation of cracks.The maximum impact load of the stitched foam sandwich composite increased by approximately 5% compared with that of the non-stitched material.In addition,the low-velocity impact damage depth,damage area and absorbed energy of the stitched three-layer foam sandwich composite were reduced by 37.7%,34.6% and 20.7%,respectively,compared with those of the non-stitched single-layer sandwich material.
文摘The mechanical properties of Ti/APC-2/Kevlar/epoxy hybrid composite laminates after low velocity impact were investigated at room temperature. There were three types of samples, including three layered [Ti/(0/90)s/Ti], five layered [Ti/(0/90)2/]s and nine layered [Ti/Kevlar/Ti/(0/90)2/]s. The lay-ups of APC-2 were crossply, while Ti layers were treated by chromic acid anodic method. Ti and APC-2 were stacked to fabricate the composite laminates via hot press curing process. Kevlar layers were added to fabricate nine-layered composite laminates via vacuum assisted resin transfer molding. The drop-weight tests were conducted with a hemispherical nosed projectile in 10 mm diameter. The impact loads were 5 kg and 10 kg and impact heights were adjusted to penetrate samples or the maximum height 1.50 m. The static tensile tests were conducted to measure the residual mechanical properties after impact. The free body drop tests were also simulated by using finite element method and software ANSYS LS-DYNA3D. The results showed that the bottom Ti layer absorbed more internal energy than the top Ti layer, then the cracks were found in the bottom Ti layer more often. The ultimate tensile strength reduced significantly after impact. The initial longitudinal compliance increased with the impact height increasing and decreased after the samples penetrated. Comparing the experimental data with the numerical results, it was found that the damage of the latter was more serious than that of the former. On the conservative side, the results of numerical simulation are acceptable and adopted for applications when no testing data available.
文摘In recent years, the development and application of high performance fiber reinforced concrete or cementitious composites are increasing due to their high ductility and energy absorption characteristics. However, it is difficult to obtain the required properties of the FRCC by simply adding fiber to the concrete matrix. Many researchers are paying attention to fiber reinforced polymers (FRP) for the reinforcement of construction structures because of their significant advantages over high strain rates. However, the actual FRP products are skill-dependent, and the quality may not be uniform. Therefore, in this study, two-way punching tests were carried out to evaluate the performances of FRP strengthened and steel and polyvinyl alcohol (PVA) fiber reinforced concrete specimens for impact and static loads. The FRP reinforced normal concrete (NC), steel fiber reinforced concrete (SFRC), and PVA FRCC specimens showed twice the amount of enhanced dissipated energy (total energy) under impact loadings than the non-retrofitted specimens. In the low-velocity impact test of the two-way NC specimens strengthened by FRPs, the total dissipated energy increased by 4 to 5 times greater than the plain NC series. For the two-way specimens, the total energy increased by 217% between the non-retrofitted SFRC and NC specimens. The total dissipated energy of the CFRP retrofitted SFRC was twice greater than that of the plain SFRC series. The PVA FRCC specimens showed 4 times greater dissipated energy than for the energy of the plain NC specimens. For the penetration of two-way specimens with fibers, the Hughes formula considering the tensile strength of concrete was a better predictor than other empirical formulae.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61473166 and 41404146)
文摘We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity intensity source(LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis(pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 10^-8 to 1 × 10^-9 atoms/s, corresponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20(m/s)/rad and the mean sensitivity of flux of 1.2 × 10^-9(atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simulation method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux,which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.
基金the Major Research Plan of the National Natural Science Foundation of China (No. 92060106)the National Natural Science Foundation of China (No. 52075541)+1 种基金the China Postdoctoral Science Foundation (No. 2019M650262)the Natural Science Foundation of Shaanxi Province, China (No. 2020JM-354)
文摘The low-velocity impact response and infrared radiation characteristics of composites have rarely been focused on simultaneously.This study aims to investigate the low-velocity impact response and infrared radiation characteristics of the glass fiber reinforced thermoplastic polypropylene and carbon fiber reinforced thermosetting epoxy resin laminates wildly used in the aircraft industry.The impact tests were conducted at five energy levels.Characterization parameters such as impact load,displacement,and absorbed energy were measured.The damage evolution and damage modes of the laminates were analyzed through active and passive thermography,ultrasonic C-scan,and optical microscope.The results indicate that Thermosets(TS)laminates exhibit better impact resistance,while Thermoplastics(TP)laminates show higher delamination ductility,and the maximum contact force of TP laminates is much smaller than that of the TS laminates under lowvelocity impacts,but the low bending stiffness and low ductility of the TP matrix cause the difference in energy absorption level between the two not significant.The temperature characteristic changes of passive infrared thermography heat maps could characterize the damage mode of the laminates.The correlation between the heat maps and the impact characteristic curves is explained;the fluctuation of the impact characteristic curves is directly related to the hot spot characteristics changes of the heat maps.More frequent curve fluctuations correspond to a larger and brighter hot spot on the heat map,which peaks at the maximum impact load after the impact force versus time curve fluctuation cutoff point,the maximum center displacement of the impact force versus displacement curve,and the maximum absorbed energy of the absorbed energy versus time curve.
基金V.Li acknowledges the financial support from the National Science Fund for Distinguished Young Scholars(Grant No.11625210)National Natural Science Foundation(Grant No.51873153)Fundamental Research Funds for the Central Universities.K.Fu acknowledges the start-up funding from Tongji University.
文摘This study details the low-velocity impact and compression-after-impact(CAI)behaviour of flax fibre-reinforced polymer(FFRP)composites.The impact resistance,energy absorption efficiency and residual compressive strength as well as the damage pattern of the FFRP composites are compared with the corresponding features of glass fibre-reinforced polymer(GFRP)composites,and the effect of the stacking sequence of FFRP composites is also investigated.The results show that the cross-ply FFRP composites have the highest impact resistance,whereas the multi-directional ply composites have the lowest impact resistance but the highest energy absorption efficiency.The energy absorption efficiency of the FFRP composites is greater than that of the GFRP composites,but the penetration resistance and residual compressive strength of the FFRP composites are lower than those of the GFRP composites with the same stacking sequence,mainly due to the lower tensile strength and elongation at fracture of the FFRP composites.It is also reported that the damage pattern of the FFRP composites is localised cracking and delamination,unlike the overall delamination failure exhibited in the GFRP composites after CAI testing.Finally,the failure mechanisms of the FFRP and GFRP composites are detailed.
文摘A theoretical solution is aimed to be developed in this research for predicting the failure in internally pressurized composite pressure vessels exposed to low-velocity impact.Both in-plane and out-of-plane failure modes are taken into account simultaneously and thus all components of the stress and strain fields are derived.For this purpose,layer-wise theory is employed in a composite cylinder under internal pressure and low-velocity impact.Obtained stress/strain components are fed into appropriate failure criteria for investigating the occurrence of failure.In case of experiencing any in-plane failure mode,the evolution of damage is modeled using progressive damage modeling in the context of continuum damage mechanics.Namely,mechanical properties of failed ply are degraded and stress analysis is performed on the updated status of the model.In the event of delamination occurrence,the solution is terminated.The obtained results are validated with available experimental observations in open literature.It is observed that the sequence of in-plane failure and delamination varies by increasing the impact energy.
基金This work was carried out with the financial support of the Russian Science Foundation(No.19-71-00147).
文摘The Grid-Characteristic numerical Method(GCM)that is quite common in solving aero and hydrodynamic problems can also be applied for mechanics of solids.It allows to implement complex border and contact conditions,including the non-reflecting border and the destructible contact.Both this conditions are very important for the precise and effective modeling of LowVelocity Impacts(LVI)on fiber and Fiber-Metal Laminates(FML)and the resulting Barely Visible Impact Damage(BVID)that influences the residual strength of a composite aircraft part.BVID is the type of damage that is not visible by the naked eye and can be hardly detected by a standard ultrasound equipment that is used for regular maintenance.It can appear during any weak impacts like bird strike or hail.Determining its influence on the residual strength of the part is very important to define the priorities of development of ultrasound diagnostics.In this paper,the GCM was applied for a full cycle of loading of an FML aircraft cover part.The FML consisted of a Carbon Fiber Reinforced Polymer(CFRP)and a single titanium layer on the upper surface.The cycle of loading in a single calculation consisted of an LVI caused by a small striker and a comparatively slow compressive in-plane loading.Three-dimensional patterns of velocity and stress distributions over the time of calculation are given.Destruction patterns,obtained via the Hashin failure criterion are given and analyzed.
基金The work was supported by the National Natural Science Foundation of China(Grant No.52172356)Hunan Provincial Innovation Foundation for Postgraduate(Grant No.CX20210384).