A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES

This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching, and to predict the in-plane effective tensile strength of the stitched composite laminates. The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties. A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching. The undistorted region, the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters, the distortion width and maximum misalignment. It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors, the stitch hole and inhomogeneous fiber content. The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite. The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]58 T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations, showing an acceptable agreement with experimental data.

Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

Impact Wear Properties of Metal-Plastic Multilayer Composites Filled with Glass Fiber Treated with Rare Earth Element Surface Modifier

The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.

IMPACT PROPERTIES OF METALLOCENE - CATALYZED ETHYLENE-α-OLEFIN COPOLYMERS

The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization.

Microstructure and impact mechanical properties of multi-layer and multi-pass TIG welded joints of Al-Zn-Mg alloy plates

The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscopy(TEM)and energy disperse spectrum(EDS),while the mechanical properties were evaluated according to the impact test.A dispersively distributed spherical and needle-likeη(MgZn2)phase was obtained in the welding seam.The phase composition of the heat-affected zone(HAZ)wasα(Al)+η(MgZn2)+Al6Mn,and there were a large number of dispersively precipitated nanoscale particles.The welded joint zone had the highest impact toughness as compared with the other parts of the joint.The MgZn2 phase in the weld zone contributed to the improved toughness of the joint.Al2 MgCu phase in HAZ was proven to act as a crack source during fracture.

Preliminary Study on Tensile and Impact Properties of Kenaf/Bamboo Fiber Reinforced Epoxy Composites

The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.

Recent research in mechanical properties of geopolymer-based ultrahigh-performance concrete:A review

Due to the growing need for sustainable and ultra-high-strength construction materials,scientists have created an innovative ultra-high-performance concrete called Geopolymer based ultra-highperformance concrete(GUHPC).Besides,in the last few decades,there have been a lot of explosions and ballistic attacks around the world,which have killed many civilians and fighters in border areas.In this context,this article reviews the fresh state and mechanical properties of GUHPC.Firstly,the ingredients of GUHPC and fresh properties such as setting time and flowability are briefly covered.Secondly,the review of compressive strength,flexure strength,tensile strength and modulus of elasticity of fibrous GUHPC.Thirdly,the blast and projectile impact resistance performance was reviewed.Finally,the microstructural characteristics were reviewed using the scanning electron microscope and X-ray Powder Diffraction.The review outcome reveals that the mechanical properties were increased when 30%silica fume was added to a higher dose of steel fibre to improve the microstructure of GUHPC.It is hypothesized that the brittleness of GUHPC was mitigated by adding 1.5%steel fibre reinforcement,which played a role in the decrease of contact explosion cratering and spalling.Removing the need for cement in GUHPC was a key factor in the review,indicating a promising potential for lowering carbon emissions.However,GUHPC research is still in its early stages,so more study is required before its full potential can be utilized.

Impact vibration properties of locally resonant fluid-conveying pipes

Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration and noise,which have a serious influence on the safety and concealment of the equipment.Based on the theory of phononic crystals,this paper studies the vibration transfer properties of a locally resonant(LR)pipe under the condition of fluid–structure interaction.The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method.Further,the different impact excitation and fluid–structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model.The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation,and the vibration reduction frequency range is near the bandgap under the fluid–structure interaction effect.Finally,the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation,and to validate the finite element model.The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.

In-Plane Impact Dynamics Analysis of Re-Entrant Honeycomb with Variable Cross-Section

Due to the unique deformation characteristics of auxetic materials(Poisson’s ratioμ<0),they have better shock resistance and energy absorption properties than traditional materials.Inspired by the concept of variable crosssection design,a new auxetic re-entrant honeycomb structure is designed in this study.The detailed design method of re-entrant honeycomb with variable cross-section(VCRH)is provided,and five VCRH structures with the same relative density and different cross-section change rates are proposed.The in-plane impact resistance and energy absorption abilities of VCRH under constant velocity are investigated by ABAQUS/EXPLICIT.The results show that the introduction of variable cross-section design can effectively improve the impact resistance and energy absorption abilities of auxetic re-entrant honeycombs.The VCRH structure has better Young’s modulus,plateau stress,and specific energy absorption(SEA)than traditional re-entrant honeycomb(RH).The influence of microstructure parameters(such as cross-section change rateα)on the dynamic impact performance of VCRH is also studied.Results show that,with the increase in impact velocity andα,the plateau stress and SEA of VCRH increase.A positive correlation is also found between the energy absorption efficiency,impact load uniformity andαunder both medium and high impact speeds.These results can provide a reference for designing improved auxetic re-entrant honeycomb structures.

Impact of Surface Passivation on the Electronic Structure and Optical Properties of the Si1-xGex Nanowires

The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.

Study on the impact force and green properties of high-velocity compacted aluminum alloy powder

High-velocity compaction （HVC） provides an effective means in the field of powder metallurgy （P/M） to reduce the porosity as well as to ameliorate the mechanical properties of products. In this study, the green density of an aluminum alloy is found to be 2.783 g cm 3. The ejection force for the aluminum alloy is in the range of 23 to 80 kN and the spring back is found to be less than 0.40%. The hardness of the green body is in the range of HRB 30 to 70. The bending strength of the green body is in the range of 6 to 26 MPa, which are higher than that of other aluminum alloys prepared by the traditional compaction method.

Nonlinear dynamic buckling of stiffened plates under in-plane impact load

This paper presents a simple solution of the dynamic buckling of stiffened plates under in-plane impact loading. Based on large deflection theory, a discretely stiffened plate model has been used. The tangential stresses of stiffeners and in-plane displacement are neglected. Appling the Hamilton's principle, the motion equations of stiffened plates are obtained. The deflection of the plate is taken as Fourier series, and using Galerkin method the discrete equations can be deduced, which can be solved easily by Runge-Kutta method. The dynamic buckling loads of the stiffened plates are obtained form Budiansky-Roth criterion.

Experimental Investigation of Mechanical Properties of Impact Modified Polyvinyl Chloride-Fly Ash Composites

The mechanical properties like tensile, pin bearing and impact properties have been studied for composites containing Fly Ash (FA) and Impact modifier (IM) in Polyvinyl Chloride (PVC) for furniture and pipe applications. Pin-bearing test is an important tool to evaluate the ability of the material to retain fasteners and the ability of the material to sustain load during the service life. The present paper evaluates the effect of variation of FA and IM on the pin bearing strength, tensile strength, modulus elongation at break and impact strength. Scanning electron microtopography indicates that the impact modifier forms a co-continuous phase at 10% of IM in PVC. Increase in void content decreases impact strength and tensile strength. As void content increases moisture absorption also increases. The results of pin bearing tests were analogous to tensile test and correlate well. Results were in accordance with impact modification theory. Moisture absorption was studied keeping in view outdoor applications.

Impact of Poly(Ester Amide) Structure on Properties and Drug Delivery for Prostate Cancer Therapy

Objective:We aim to develop a polymer library consisting of phenylalanine-based poly(ester amide)s(Phe-PEAs)for cancer therapy and investigate the structure–property relationship of these polymers to understand their impact on the drug delivery efficiency of corresponding nanoparticles(NPs).Impact Statement:Our study provides insights into the structure–property relationship of polymers in NP-based drug delivery applications and offers a potential polymer library and NP platform for enhancing cancer therapy.Introduction:Polymer NP-based drug delivery systems have demonstrated substantial potential in cancer therapy by improving drug efficacy and minimizing systemic toxicity.However,successful design and optimization of these systems require a comprehensive understanding of the relationship between polymer structure and physicochemical properties,which directly influence the drug delivery efficiency of the corresponding NPs.Methods:A series of Phe-PEAs with tunable structures was synthesized by varying the length of the methylene group in the diol part of the polymers.Subsequently,Phe-PEAs were formulated into NPs for doxorubicin(DOX)delivery in prostate cancer therapy.Results:Small adjustments in polymer structure induced the changes in the hydrophobicity and thermal properties of the PEAs,consequently NP size,drug loading capacity,cellular uptake efficacy,and cytotoxicity.Additionally,DOXloaded Phe-PEA NPs demonstrated enhanced tumor suppression and reduced side effects in prostate tumor-bearing mice.Conclusion:Phe-PEAs,with their finely tunable structures,show great promise as effective and customizable nanocarriers for cancer therapy.

THE IMPACT PROPERTIES OF HYBRID COMPOSITES

In this paper an experimental investigation on the impact behaviour of hybrid composites is conducted by instrumental Charpy impact test. The variation of impact strength and impact toughness index of C/K and C/G hybrid composites of different matrices with hybrid ratio and interface number is revealed. The dynamic hybrid effect is also investigated from different aspects. Meanwhile, the estimating model for impact strength is established and the estimated values are in good agreement with experimented ones. The hybrid effect coefficients based on different definitions are organically related by the model. This provides a basis for the further study of the impact constitutive equation of hybrid composites.

Effect of Velocity of Impact on Mechanical Properties and Microstructure of Medium Carbon Steel during Quenching Operations

Theoretical analysis of the effects of velocity of impact using suitable heat transfer equations expressed in forms of finite difference method was developed and used to determine their effects on the characteristic cooling parameters during quenching process. Various velocities of impact obtained by varying the heights of specimen drops were also used to experimentally determine their effects on characteristic cooling parameters and mechanical properties of medium carbon steel using water as the quenching medium. At height of drop of 0.5 m, 1.0 m, 1.5 m, and 2.0 m, the tensile strength of the material is 410.4, 496.12, 530.56, and 560.40 N/mm2 respectively. The corresponding hardness values are 42.4, 45.2, 46.2, 50.5 HRC respectively. It is found that as the velocity of impact increases, maximum cooling rate increases. Hardness and ultimate tensile strength also increase. There are good agreements between theoretical and experimentally determined values of critical cooling parameters of water during quenching operations.

A Comparative Analysis of Chemical Properties and Factors Impacting Spring Sea Fog over the Northwestern South China Sea

In the present study,we analyzed the chemical properties and factors impacting the sea fog water during two sea fog events over the northwestern South China Sea in March 2017,and compared our results with those of other regions.The sea fog water during these two events were highly acidic and their average pH was below 3,which was related to the high initial acidifying potential and large amounts of NOand SOnot involved in the neutralization reaction.The dominant cations in the sea fog water were Naand NH.The primary anions in the sea fog water over the South China Sea were Cland NO,while that over the North Pacific Ocean was mainly SO,and ratios of the three fog water ions near the Donghai Island were similar.Ions in the sea fog water during the two events were mainly derived from marine aerosols,while the difference was that the first low-level sea fog airflow trajectory passed over Hainan Island.Therefore,the proportion of K+in the first sea fog was much higher than that in sea water and the second.Sulfate was the key to fog water nucleation,which made ion concentration in the sea fog water during the second event higher than that during the first.A decrease in average diameter during the first sea fog formation led to an ion concentration increase,while the average diameter of sea fog water during the second event was lower than that during the first,which corresponded with a moderate ion concentration increase.

Fiber Loading of Date Palm and Kenaf Reinforced Epoxy Composites:Tensile,Impact and Morphological Properties

Date palm fiber(DPF)and kenaf fiber were reinforced in epoxy having various fiber loading 40%,50%,and 60%by weight.These hybrid samples were manufactured by hot press technique and then characterized for tensile,impact,and morphological behavior to evaluate the ratio of fibers in the hybrid composites;the addition of kenaf improved the tensile properties,Scanning Electron Microscopy(SEM)revealed the interfacial bonding of fiber/matrix,and dispersion and void content in composites.Impact test studies reflected the effect of natural fiber with epoxy,level of stress transfer from matrix to reinforced material,and reinforced material’s role in absorbing the impacts.It showed that 50%of DPF had the best shock-absorbing capacity.The obtained results indicated that 30%DPF in hybrid composite showed improved tensile properties and homogeneous distribution of fiber without void content;however,50%DPF loading in hybrid composites had the best impact properties.

Comparative Study of Tensile and Charpy Impact Properties of X70 and X80 Linepipe Steels After Ultra Fast Cooling Processing

Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown that the mechanical properties satisfy all the standard requirements of the X70 and X80 steels. UFC results in a presence of microstructure containing quasi polygonal（QF）, acicular ferrite（AF） and granular bainite（GB）. The alloying elements and UFC enhance the strengthening contribution caused by solid solution, dispersion, dislocation and precipitation strengthening. The size and distribution of precipitates in the linepipe steels are fine and dispersed. MA is also homogeneously dispersed due to UFC. Average grain size in the X80 steel is finer than that in the X70 steel. The volume fractions of secondary phases in the X80 steel are greater than those in the X70 steel. The X80 steel remains finer and more dispersed precipitates compared to the X70 steel. As a result, the tensile properties of X80 steel are higher than those of X70 steel. The Charpy absorbed energies of X70 and X80 steels at-10 ℃ reached 436 and 460 J, respectively. They reached 433 and 461 J at-15 ℃, respectively. This is mainly attributed to the presence of larger amounts of AFs in the X80 steel. A microstructure of AF for the X80 steel results in combining high strength and high toughness.