Fatigue Reliability Analysis of Fiber-Reinforced Laminated Composites by Continuum Damage Mechanics

This paper investigates the reliability of composite laminates with various lay-ups under fatigue loading.The prediction of failure probability of composite laminates subjected to different loads involves many uncertainties associated with mechanical properties,loading,and boundary conditions.Failure in the composite material is truly hard to trace because there are individual faults in each ply,and we face a stochastic process due to the scatter in the mechanical properties.The continuum damage mechanics(CDM),as a powerful approach,is applied to model the damage of fiber,matrix,and fiber/matrix debonding.This method defines criteria for damage detection and determines safe zones.The material constitutive equations are executed using a subroutine inAbaqus.The first-order reliability method and second-order reliability method have been applied to examine the reliability of laminated composites.The results are compared with those of the Monte Carlo simulation.Different composite laminates under different stress levels are considered for the failure probability investigation.The limit state functions and random variables have been determined based on the CDM model.Finally,the effects of the number of cycles,applied stress,and stacking sequence of the laminate on the reliability and fatigue life in fiber-reinforced laminated composites are assessed.

Snap-through behaviors and nonlinear vibrations of a bistable composite laminated cantilever shell:an experimental and numerical study

The snap-through behaviors and nonlinear vibrations are investigated for a bistable composite laminated cantilever shell subjected to transversal foundation excitation based on experimental and theoretical approaches.An improved experimental specimen is designed in order to satisfy the cantilever support boundary condition,which is composed of an asymmetric region and a symmetric region.The symmetric region of the experimental specimen is entirely clamped,which is rigidly connected to an electromagnetic shaker,while the asymmetric region remains free of constraint.Different motion paths are realized for the bistable cantilever shell by changing the input signal levels of the electromagnetic shaker,and the displacement responses of the shell are collected by the laser displacement sensors.The numerical simulation is conducted based on the established theoretical model of the bistable composite laminated cantilever shell,and an off-axis three-dimensional dynamic snap-through domain is obtained.The numerical solutions are in good agreement with the experimental results.The nonlinear stiffness characteristics,dynamic snap-through domain,and chaos and bifurcation behaviors of the shell are quantitatively analyzed.Due to the asymmetry of the boundary condition and the shell,the upper stable-state of the shell exhibits an obvious soft spring stiffness characteristic,and the lower stable-state shows a linear stiffness characteristic of the shell.

Flexible,high-density,laminated ECoG electrode array for high spatiotemporal resolution foci diagnostic localization of refractory epilepsy

High spatiotemporal resolution brain electrical signals are critical for basic neuroscience research and high-precision focus diagnostic localization,as the spatial scale of some pathologic signals is at the submillimeter or micrometer level.This entails connecting hundreds or thousands of electrode wires on a limited surface.This study reported a class of flexible,ultrathin,highdensity electrocorticogram(ECoG)electrode arrays.The challenge of a large number of wiring arrangements was overcome by a laminated structure design and processing technology improvement.The flexible,ultrathin,high-density ECoG electrode array was conformably attached to the cortex for reliable,high spatial resolution electrophysiologic recordings.The minimum spacing between electrodes was 15μm,comparable to the diameter of a single neuron.Eight hundred electrodes were prepared with an electrode density of 4444 mm^(-2).In focal epilepsy surgery,the flexible,high-density,laminated ECoG electrode array with 36 electrodes was applied to collect epileptic spike waves inrabbits,improving the positioning accuracy of epilepsy lesions from the centimeter to the submillimeter level.The flexible,high-density,laminated ECoG electrode array has potential clinical applications in intractable epilepsy and other neurologic diseases requiring high-precision electroencephalogram acquisition.

Effects of Sinusoidal Vibration of Crystallization Roller on Composite Microstructure of Ti/Al Laminated Composites by Twin-Roll Casting

A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites,and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail.The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing,instead of transition bonding by forming metal compound layer.The meshing depth between titanium and aluminum layers (6.6μm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm,vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1μm),and the composite interfacial strength(27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm).This is because with the action of high-speed superposition of strong tension along the rolling direction,strong pressure along the width direction and rolling force,the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line",and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling,which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality.

Mechanical behaviour of fiber-reinforced grout in rock bolt reinforcement

Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essential for understanding its performance in ground support.To date,few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout(FRG)in rock bolt reinforcement.Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression,indirect tension,and direct shear loading conditions.We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG.FRG was developed using 15%silica fume(SF)replacement of cement(by weight)and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout.Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality.The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined.Our experimental results showed that the addition of SF and steel fiber by 1.5%fiber volume proportion could lead to the highest compressive,tensile,and shear strengths of the grout.The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%.The scanning electron microscopy(SEM)analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout.Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar’s load carrying capacity.Therefore,FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

Fractures interaction and propagation mechanism of multi-cluster fracturing on laminated shale oil reservoir

The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina,which is characterized by strong plasticity and developed longitudinal shell limestone interlayer.To improve the production efficiency of reservoirs by multi-cluster fracturing,it is necessary to consider the unbalanced propagation of hydraulic fractures and the penetration effect of fractures.This paper constructed a numerical model of multi-fracture propagation and penetration based on the finite element coupling cohesive zone method;considering the construction cluster spacing,pump rate,lamina strength and other parameters studied the influencing factors of multi-cluster fracture interaction propagation;combined with AE energy data and fracture mode reconstruction method,quantitatively characterized the comprehensive impact of the strength of thin interlayer rock interfaces on the initiation and propagation of fractures that penetrate layers,and accurately predicted the propagation pattern of hydraulic fractures through laminated shale oil reservoirs.Simulation results revealed that in the process of multi-cluster fracturing,the proportion of shear damage is low,and mainly occurs in bedding fractures activated by outer fractures.Reducing the cluster spacing enhances the fracture system's penetration ability,though it lowers the activation efficiency of lamina.The high plasticity of the limestone interlayer may impact the vertical propagation distance of the main fracture.Improving the interface strength is beneficial to the reconstruction of the fracture height,but the interface communication effect is limited.Reasonable selection of layers with moderate lamina strength for fracturing stimulation,increasing the pump rate during fracturing and setting the cluster spacing reasonably are beneficial to improve the effect of reservoir stimulation.

Theoretical and experimental investigation of the resonance responses and chaotic dynamics of a bistable laminated composite shell in the dynamic snap-through mode

The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified.The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method.The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed.The discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance responses.The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system.Furthermore,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare maps.Finally,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.

Inter-well internal resonance analysis of rectangular asymmetric cross-ply bistable composite laminated cantilever shell under transverse foundation excitation

The chaotic dynamic snap-through and complex nonlinear vibrations are investigated in a rectangular asymmetric cross-ply bistable composite laminated cantilever shell,in cases of 1:2 inter-well internal resonance and primary resonance.The transverse foundation excitation is applied to the fixed end of the structure,and the other end is in a free state.The first-order approximate multiple scales method is employed to perform the perturbation analysis on the dimensionless two-degree-of-freedom ordinary differential motion control equation.The four-dimensional averaged equations are derived in both polar and rectangular coordinate forms.Deriving from the obtained frequency-amplitude and force-amplitude response curves,a detailed analysis is conducted to examine the impacts of excitation amplitude,damping coefficient,and tuning parameter on the nonlinear internal resonance characteristics of the system.The nonlinear softening characteristic is exhibited in the upper stable-state,while the lower stable-state demonstrates the softening and linearity characteristics.Numerical simulation is carried out using the fourth-order Runge-Kutta method,and a series of nonlinear response curves are plotted.Increasing the excitation amplitude further elucidates the global bifurcation and chaotic dynamic snap-through characteristics of the bistable cantilever shell.

Study of damage behavior and repair effectiveness of patch repaired carbon fiber laminate under quasi-static indentation loading

Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.

Dynamic and electrical responses of a curved sandwich beam with glass reinforced laminate layers and a pliable core in the presence of a piezoelectric layer under low-velocity impact

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.

A refined finite element method for bending analysis of laminated plates integrated with piezoelectric fiber-reinforced composite actuators

This research presents a finite element formulation based on four-variable refined plate theory for bending analysis of cross-ply and angle-ply laminated composite plates integrated with a piezoelectric fiber-reinforced composite actuator under electromechanical loading. The four-variable refined plate theory is a simple and efficient higher-order shear deformation theory, which predicts parabolic variation of transverse shear stresses across the plate thickness and satisfies zero traction conditions on the plate free surfaces. The weak form of governing equations is derived using the principle of minimum potential energy, and a 4-node non-conforming rectangular plate element with 8 degrees of freedom per node is introduced for discretizing the domain. Several benchmark problems are solved by the developed MATLAB code and the obtained results are compared with those from exact and other numerical solutions, showing good agreement.

Lagged strain of laminates in RC beams strengthened with fiber-reinforced polymer

Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.

Experimental study of polyurea-coated fiber-reinforced cement boards under gas explosions

Five types of polyurea elastomers were synthesized by changing the isocyanate component and the mechanical properties of polyurea materials were measured. Fiber-reinforced cement boards(FRCB)strengthened by polyurea with different formulations were processed, and a series of experiments were carried out on the specimens with gas explosion devices. The results showed that the conventional mechanical properties of different types of polyureas had their own advantages. Based on the gas explosion overpressure criterion, the blast resistances of reinforced plates were quantitatively evaluated,and the best polyurea was selected to guide the formulation design. The three typical failure modes of polyurea-reinforced FRCBs were flexural, shear, and flexural-shear failure. Dynamic thermodynamics and shock wave spectral analysis revealed that the polyurea did not undergo a glass transition in the gas explosion tests but retained its elastic properties, allowing it to effectively wrap the fragments formed by the brittle substrates.

Multi-stage penetration characteristics of thick ultra-high molecular weight polyethylene laminates

To further reveal the failure mechanisms of thick ultra-high molecular weight polyethylene(UHMWPE)laminates,field firing tests were conducted for 10-,20-,and 30-mm thick laminates against 12.7-mm calibre wedge-shaped fragment simulated projectiles at high velocities between 450 and 1200 m/s.The ballistic performance,deformation process,and staged failure characteristics of the laminates with different thicknesses were compared and analysed.The results demonstrate that the ballistic limits of the UHMWPE laminates increase almost linearly with laminate thickness.The 10-mm thick laminate generally experiences two-stage failure characteristics,whereas three-staged failure occurs in the 20-and 30-mm thick laminates and the progressive delamination is evident.The energy limit concept representing the maximum energy absorption efficiency and the idea of reuse of the thick UHMWPE laminates are proposed in this study.The findings of this research will be useful in the design of flexible and effective UHMWPE-based protective equipment.

Ballistic penetration damages of hybrid plain-woven laminates with carbon,Kevlar and UHMWPE fibers in different stacking sequences

Hybrid composite materials combine different fibers in preform and take advantages of different mechanical behaviors for improving ballistic impact damage tolerances.Here we report ballistic impact damages of plain-woven laminates with different hybrids and stacking sequences.Three kinds of hybrid laminates,i.e.,carbon/Kevlar,carbon/ultra-high molecular weight polyethylene(UHMWPE),and UHMWPE/Kevlar,had been prepared and tested in ballistic penetration with fragment simulating projectiles(FSP).The residual velocities of the projectiles and impact damage morphologies of the laminates have been obtained to show impact energy absorptions for the different hybrid schemes.A microstructural model of the hybrid laminates had also been established to show impact damage mechanisms with finite element analysis(FEA).We found that the UHMWPE/Kevlar hybrid laminates with Kevlar layers as the front face have the highest energy absorption capacity,followed by the carbon/Kevlar hybrid laminates with carbon layers as the front face.The main damage modes are fiber breakages,matrix crack and interlayer delamination.The ballistic damage evolutions from the FEA results show that the major damage is shear failure for front layers,while tension failure for the back layers.We expect that the ballistic impact performance could be improved from the different hybrid schemes.

Dynamic analysis of bio-inspired helicoid laminated composite plates resting on Pasternak foundation excited by explosive loading

This paper uses isogeometric analysis(IGA)based on higher-order shear deformation theory(HSDT)to study the dynamic response of bio-inspired helicoid laminated composite(B-iHLC)plates resting on Pasternak foundation(PF)excited by explosive loading.IGA takes advantage of non-uniform rational Bspline(NURBS)basic functions to exactly represent the structure geometry models and the attainment of higher-order approximation conditions.This method also ensures a C1 continuous function in the analysis of transverse shear deformation via HSDT.Furthermore,IGA eliminates the requirement for correction factors and delivers accurate results.Pasternak foundation with two stiffness parameters:springer stiffness(k_(1))and shear stiffness(k_(2)).The derivation of the governing equations is based on Hamilton's principle.The proposed method is validated through numerical examples.A comprehensive analysis of the impact of geometrical parameters,material properties,boundary conditions(BCs),and foundation stiffness on dynamic response of B-i HLC plates is carried out.

Effects of Hydrothermal Environment on the Deformation of the Thin Bamboo Bundle Veneer Laminated Composites

To overcome warping in thin bamboo bundle veneer laminated composites(TBLC),their hydrothermal deformation characteristics were systematically investigated in this study.It was found that TBLCs accelerated the release of internal stress in the thickness direction in a hydrothermal environment,which increased their warpage.TBLCs showed increased warpage in the width and diagonal directions upon increasing the temperature.The warpage of Type E increased by 155.88%and 66.67%in the width and diagonal directions,respectively,when the temperature increased from 25
C to 100
C.The symmetrical TBLC with cross-lay-up and odd layers displayed better hydrothermal stability.We revealed that the deformation of the TBLCs could be regulated under the synergistic effect of water and temperature.These results provide a scientific basis for improving the uniformity of bamboo bundle composite materials and for developing thin bamboo bundle fiber composite materials with designable structures and controllable performance.

Vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers under blast load

In this article,vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers subjected to blast load are studied.Higher-order ES-MITC3 element based on higher-order shear deformation theory(HSDT)to achieve the governing equations.The sandwich plates with the ultra-light feature of the auxetic honeycomb core layer(negative Poisson’s ratio)and reinforced by two laminated three-phase skin layers.The obtained results in our work are compared with other previously published to confirm accuracy and reliability.In addition,the effects of parameters such as geometrical and material parameters on the vibration characteristics of sandwich plates with an auxetic honeycomb core and laminated three-phase skin layers are fully investigated.

Effect of Molding Technique That Move Model Position Just before Formation in Production of Laminated Mouthguard

Many molding techniques have been researched to ensure the thickness of custom mouthguards. The aim of this study was to clarify the effect on the thickness of a laminated mouthguard of a molding technique in which the model position is moved forward just before molding. Mouthguards were molded using a 3.0-mm-thick ethylene vinyl acetate mouthguard sheet and a pressure molding machine. The molding method was the normal molding method (condition C) and the molding technique (condition MP) in which the model position was moved 20 mm forward just before molding. Regarding the molding of the first layer (F) and the second layer (S), the following four molding methods based on the combination of conditions C and MP were compared;FC-SC, FC-SMP, FMP-SC, and FMP-SMP. Differences in mouthguard thickness due to molding conditions for the first and second layers were analyzed by two-way ANOVA and Bonferroni’s multiple comparison test. Significant differences were observed among all molding conditions on the labial surface, and the thicknesses were in the order FC-SC < FC-SMP < FMP-SC < FMP-SMP. FMP-SMP was 4.67 mm thick, which was 1.39 mm thicker than FC-SC. FC-SC was the thinnest at the cusp, and a significant difference was observed between other molding conditions. On the buccal side, significant differences were observed between all conditions except FC-SMP and FMP-SC, and the thicknesses were in the order FC-SC < FC-SMP, FMP-SC < FMP-SMP. The results of this study suggested that the labial and buccal sides of laminated mouthguards could be made 1.4 and 1.2 times thicker when a molding technique that moves the model position just before formation was used for the first and second layers. The reduction in thickness was suppressed by approximately 23.2% and approximately 10.7% on the labial and buccal sides, respectively, compared with the normal molding method.

Vacuum-free lamination via controlled polymer adhesion for selective photogeneration and photodetection

This study attempts to develop a reproducible thin-film formation technique called vacuum-free(VF)lamination,which transfers thin films using elastomeric polymer-based laminating mediators.Precisely,by controlling the interface characteristics of the mediator based on the work of adhesion,VF lamination is successfully performed for various thicknesses(from 20 to 240 nm)of a conjugated photoactive material composed of poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-bʹ]dithiophene))-alt-(5,5-(1ʹ,3ʹ-di-2-thienyl-5ʹ,7ʹ-bis(2-ethylhexyl)benzo[1ʹ,2ʹ-c:4ʹ,5ʹ-cʹ]dithiophene-4,8-dione)](a polymer donor)and 2,2ʹ-((2Z,2ʹZ)-((12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2ʹʹ,3ʹʹ:4ʹ,5ʹ]thieno[2ʹ,3ʹ:4,5]pyrrolo[3,2-g]thieno[2ʹ,3ʹ:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile(a nonfullerene acceptor).Interestingly,the organic photovoltaic and photodetecting applications,prepared by the VF lamination process,showed superior performance compared to those of devices prepared by conventional spin-coating.This is due to the overturned surface morphology,which led to enhanced charge transport ability and blocking of the externally injected charge.Thus,the reproducible VF lamination process,exploiting an adhesion-based elastomeric polymer mediator,is a promising thin-film formation technique for developing efficient next-generation organic optoelectronic materials consistent with the solution process.