Quasi-static Rates Research Articles

The effect of loading rate on the compression properties of carbon fibre-reinforced epoxy honeycomb structures

The effect of varying strain rate on the compression strength and energy absorption characteristics of a carbon fibre-reinforced plastic honeycomb core has been investigated over a wide range of loading rates. The honeycombs were manufactured by infusing an epoxy resin through a carbon fibre fabric positioned in a dismountable honeycomb mould. The vacuum-assisted resin transfer moulding technique yielded honeycomb cores of a high quality with few defects. Compression tests were undertaken on single and multiple cells and representative volumes removed from the cores in order to assess how the compression strength and specific energy absorption vary with test rate. Crushing tests over the range of strain rates considered highlighted the impressive strength and energy-absorbing response of the honeycomb cores. At quasi-static rates of loading, the compression strength and specific energy absorption characteristics of the unidirectional samples exceeded those of the multidirectional cores. Here, extensive longitudinal splitting and fibre fracture were the predominant failure mechanisms in the cores. For all three stacking sequences, the single-cell samples offer higher compression strength than their five-cell counterparts. In contrast, the specific energy absorption values were found to be slightly higher in the five-cell cores. The experiments highlighted a trend of increased compression strength with loading rate in the multidirectional samples, whereas the strength of the [0°]4 samples was relatively insensitive to strain rate. Finally, the energy absorbing capacity of all structures studied was found to be reasonably constant at increasing rates of strain.

Evaluation of grit-blasting as a pre-treatment for carbon-fibre thermoplastic composite to aluminium bonded joints tested at static and dynamic loading rates

Light-weighting of transportation structures necessitates multi-material design employing composites and aluminium, with thermoplastic composites being of increasing interest to the industry. Adhesive bonding is a viable solution for joining dissimilar materials, but joint performance can be considerably affected by surface preparation. In this paper, alumina grit-blasting is investigated as a surface preparation technique for thermoplastic-matrix composites to be bonded to aluminium alloys. Grit-blasting is performed on composite adherends for varying durations, and the resulting chemical and morphological modifications are analysed using goniometry, profilometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Adhesively-bonded single-lap joints are tested at quasi-static and dynamic (0.5 m/s) loading rates, and fractography analysis is performed at macro and micro scales. It is found that high lap shear strength and work-to-failure can be achieved through optimisation of the grit-blasting parameters. The optimised process produces a composite surface with plasticised matrix, minimal fibre exposure, and favourable surface chemistry for adhesive bonding. Grit-blasting can thus be a simple, yet effective surface preparation technique for composites to be bonded to aluminium.

Deformation modes and crashworthiness energy absorption of sinusoidally corrugated tubes manufactured by direct metal laser sintering

Thin-walled structures are used for crashworthiness energy absorption applications such as automobile vehciles and aircraft. Structures of sinusoidally corrugated profiles were of great interest because of their ability to reduce the peak crushing forces and provide stable energy-absorbing patterns. Studies on structures of sinusoidally corrugated profiles are limited to numerical studies due to manufacturing limitations. Advancement in additive manufacturing enables the fabrication of structures of complex profiles such as corrugated tubes. This could solve the issue of mass productions of such structures for energy absorption applications. This paper aims to additively manufacture and test sinusoidally corrugated tubes experimentally. A sample of 8 sinusoidally corrugated tubes was additively manufactured and tested under a quasi-static displacement rate of 20 mm/min. The results showed that corrugated tubes exhibit lower and stable crushing forces compared to conventional straight tubes. It was found that increasing the wavelength from 10 to 20 mm results in changing deformation mode from ring to diamond, while increasing the amplitude from 1 to 2 mm has no effect when the thickness is 1 mm. Corrugated tubes achieved a maximum peak force reduction of 75%, and a maximum crushing force efficiency increase of 63%. However, they also resulted in a reduction of 46 and 55% in energy absorption and specific energy absorption, respectively.

Failure behavior of woven fiberglass composites under combined compressive and environmental loading

The purpose of this study is to quantitatively characterize the compressive and damage behavior of a woven fiberglass composite under combined environmental loading. Cuboidal samples of a commercially available woven fiberglass epoxy resin composite, garolite G10, are examined under uniaxial compressive loading perpendicular to the plies at quasi-static (10−3 s−1) and dynamic (103 s−1) strain rates using a standard load frame and Kolsky (split-Hopkinson) bar. In order to simulate environmental conditions, a subset of samples were soaked in either distilled or ASTM standard seawater prior to loading. Two time periods of environmental conditioning were investigated: short term at two weeks and long term at four months. Results demonstrate that, on average, the dynamic compressive strength of the fiberglass increased 35% from the quasi-static. Moreover, environmentally treated samples generally experienced a decrease strain to failure, and composites exposed to water for only short periods exhibited signs of the absorbed water sustaining additional load under quasi-static rates. Ultra-high-speed photography combined with digital image correlation, a full-field surface kinematic measurement technique, is used to map 2D strains on the sample during loading. In all cases, a clear shear failure mechanism from local instabilities appears, and a Mohr–Coulomb failure criterion is used to extract a mesoscale cohesive shear stress and coefficient of internal friction.

Microstructural and mechanical characterization of variability in porous advanced ceramics using X-ray computed tomography and digital image correlation

This paper explores microstructural and mechanical variability in porous ceramics, combining advanced X-ray computed tomography (XCT) and digital image correlation (DIC) techniques to characterize an alumina material. The results show low variability in microstructure, with median pore size values for this alumina ranging from 16.0 μm to 17.2 μm across ten samples. Spatial analysis showed internal pores are regularly distributed, and though spacing was found to be largely independent of pore size, the variability in spacing was shown to be greater for smaller pores. Mechanical results show a strain-rate dependence and greater scatter at quasi-static rates, with the coefficient of variation for compressive strength and failure strain decreasing from 10.28% and 10.23% at quasi-static to 5.20% and 4.17% at dynamic rates. In view of the consistency demonstrated in the microstructure, the difference in variability between the quasi-static and dynamic mechanical properties is attributed to variability in testing conditions (e.g., misalignment of platens) and the activation of a greater number of pores in dynamic compression. In summary, these results motivate the use of new spatial characterization parameters via XCT for links to manufacturing, the integration of realistic microstructures into computational models, and focus on the role of defect distributions in dynamic compressive failure events.

Modeling the transient behavior of the NiTi shape memory actuator using finite element analysis: Parametric study of the rate effects

Finite element simulation is presented to study the rate effects of the shape memory response of bent NiTi wire “C-shaped” exposure to load. A three-dimensional constitutive model for shape memory alloys proposed by Auricchio is implemented in the built-in library of Ansys Workbench 18.2 to capture the shape memory behavior of three different NiTi alloys that are subjected to different thermomechanical treatments. The quasi-static (slow) loading rate and the dynamic (fast) loading rate have been applied isothermally or at adiabatic conditions. Other models assumed the classical shape memory stress-strain behavior, but the realistic behavior of the NiTi SMA is different. The NiTi SMA is influenced by its microstructural changes, such as internal defects, grain size, chemical compositions, content of dislocations and density; all these effects should be added when modeling, which has been considered in this study. The results showed a significant effect of the dynamic loading of NiTi on decreasing the recoverable strain. As a result, it could be expected that the actuator lifetime could be reduced when a rapid, as opposed to a slow, loading rate is adopted. Inhomogeneity of stresses and deformations after loading can cause irreversible plastic deformation. The complete deformation recovery is noticed in the reorientation scenario, unlike in the SIM scenario, which exhibits unrecoverable deformation. Experimental validation is done by comparing the macroscopic displacement of the bent NiTi actuator with the model results, which shows good agreement.

Real-time visualization of dynamic fractures in porcine bones and the loading-rate effect on their fracture toughness

We visualized, in real time, the dynamic fracture behaviors in porcine cortical bone from humerus and porcine trabecular bone from nasal bone at a high loading rate using high-speed synchrotron X-ray phase-contrast imaging (PCI). Dynamic three-point bending loading was applied on notched bone specimens by a modified Kolsky compression bar and images of the entire fracture events were recorded with an ultra-high-speed camera. Experiments at a quasi-static loading rate on material testing system (MTS) were also performed to identify the loading-rate effects on the fracture toughness of the two types of bone. Three-dimensional synchrotron X-ray computed tomography was conducted to examine the initial microstructures in the bone specimens before mechanical loading. At the dynamic loading rate, the onset locations of crack initiation were found to be independent from the bone types. The deleterious effect of dynamic loading rate on bone's fracture toughness was verified in this study and the crack was found to propagate at higher speeds in cortical bone than in trabecular bone. In a comparison of the observed more torturous crack paths at the quasi-static loading rate, cracks in dynamically loaded bone specimens generally followed the paths with less in-plane deflections and out-of-plane twists. However, our experimental results also indicated that, although the extent was diminished at dynamic loading rate, the crack deflections at osteon cement lines still played a role as a major toughening mechanism to dynamic fractures in transversely orientated cortical bone.

The mechanical behaviour of spherical egg-box sandwich structures

Abstract This paper presents a study on the mechanical properties of spherical egg-box core sandwich panels subjected to compression. Initial attention focuses on the effect that constraining the core, via the introduction of skins, and increasing the thickness of the cell walls has on the compressive properties of GFRP and CFRP structures. Tests were also undertaken on foam-filled samples in order to investigate the influence of additional support on the crushing behaviour of the cores. Low velocity impact tests were subsequently undertaken in order to investigate the rate-sensitivity of these core structures. Finally, blast tests were conducted on the core materials to investigate their response at high strain rates. It has been shown that constraining the lateral movement of the cores, by bonding composite skins to the upper and lower surfaces, serves to enhance the mechanical properties of the core in compression. In addition, quasi-static compression testing has shown that the compressive strength of the core increases rapidly with increasing cell wall thickness, with effects being more pronounced in the GFRP structures. Tests on foam-filled panels have shown that adding a low density filler to the core serves to enhance the energy-absorbing properties of the GFRP systems. Subsequent tests at dynamic rates of loading have shown that the values of energy absorption were slightly higher than those measured at quasi-static rates, due to rate effects in the failure processes within the composite material. Finally, it has been shown that when subjected to blast loading, extensive crushing of the spherical egg-box was observed, indicating that these structures are capable of absorbing significant energy under this extreme loading condition.

Dynamic Behaviour of a High-Strength Structural Steel at Low Temperatures

The main objective of this experimental study is to determine the effect of low temperatures on the mechanical behaviour of Strenx 960 Plus high-strength structural steel at different strain rates and stress triaxialities. For this purpose, a comprehensive experimental campaign was designed to characterise the material at a wide range of temperatures and loading rates. The stress triaxiality was varied by testing specimens with different geometry. First, to determine the ductile-to-brittle transition temperature, instrumented Charpy V-notch impact tests were carried out at a range of temperatures from + 20 °C down to − 90 °C. The impact energy dropped gradually with decreasing temperature, but a clear transition temperature could not be identified. A fractography study exhibited a clear dimple structure, revealing predominantly ductile fracture at all temperatures. Then, uniaxial tension tests on smooth and pre-notched axisymmetric specimens under both quasi-static and dynamic loading rates were carried out at room temperature and low temperatures. These tests were conducted to characterise the rate-dependence of the stress–strain behaviour and the failure strain. The results revealed that under quasi-static conditions the flow stress increased with decreasing temperature, while the failure strain was nearly independent of the temperature. Dynamic tensile tests using the same specimen geometries were conducted in a split Hopkinson tension bar at + 20 °C and − 40 °C. The material exhibited a positive strain rate sensitivity at all investigated temperatures. This experimental study reveals that the Strenx 960 Plus steel retains its ductility at temperatures as low as − 40 °C. Brittle failure could not be observed even with combined high strain rate, high stress triaxiality and low temperature.

Bipropellant high energy stimulation for oil and gas applications

Large-scale extraction of oil and natural gas requires an effective method of generating a high surface area network of fractures, or the stimulation of existing fractures, in a formation in order to increase permeability. Conventional hydraulic fracturing has limited utility in this application. In this work, Sandia National Laboratories is exploring high rate pressurization techniques employing tailored energetic materials systems to control both pressure rise rate and peak pressure in order to optimally stimulate potential rock formations. Rapid pressurization, at rates far exceeding quasi-static conventional hydraulic rates, can generate multiple radial well bore fractures and potentially provide a mechanism to induce shear destabilization within the formation that enables the fractures to be self-propping. Multiple fractures from the well bore allow efficient coupling to the existing formation fracture network and increase near field well bore permeability. Furthermore, these techniques can allow for repeated stimulations and produce energetic events within the fractures thereby allowing fractures to be extended further. Controlled rate pressurization is a useful tool for the efficient generation of fracture networks and has potential application to increase oil and gas production. This paper provides an overview of the concept of controlled rate pressurization, laboratory experiments and field trials that are being conducted. The present work investigates detonations of a stoichiometric mixture of ethylene and nitrous oxide (C2H4 + 6N2O) at high initial pressures ranging from 0.862 to 2.068 MPa as a method of fracturing rock below the ground surface. The experiments investigate the fracture generation as a function of the initial pressure of the mixture. In the current configuration, the combustion reaction is initiated by an electrically fired igniter at the ground surface and quickly transitions to a detonation. The experimental setup accommodates one high pressure (690 MPa) transducer, placed downstream of the igniter, to measure peak pressure. The pressure transducer recorded peak pressures, which are 2.3–2.6 times in excess of the Chapman-Jouguet (CJ) values as a result of pre-compression of the unburned gas mixture during the flame acceleration prior to deflagration-to-detonation transition (DDT). Analysis of the data indicated an increase in rock permeability due to detonations and this was confirmed by the core drilled sections at the test site.

Mechanical response, twinning, and texture evolution of WE43 magnesium-rare earth alloy as a function of strain rate: Experiments and multi-level crystal plasticity modeling

This work adapts a recently developed multi-level constitutive model for polycrystalline metals that deform by a combination of elasticity, crystallographic slip, and deformation twinning to interpret the deformation behavior of alloy WE43 as a function of strain rate. The model involves a two-level homogenization scheme. First, to relate the grain level to the level of a polycrystalline aggregate, a Taylor-type model is used. Second, to relate the aggregate level response at each finite element (FE) integration point to the macro-level, an implicit FE approach is employed. The model features a dislocation-based hardening law governing the activation stress at the slip and twin system level, taking into account the effects of temperature and strain rate through thermally-activated recovery, dislocation debris formation, and slip-twin interactions. The twinning model employs a composite grain approach for multiple twin variants and considers double twinning. The alloy is tested in simple compression and tension at a quasi-static deformation rate and in compression under high strain rates at room temperature. Microstructure evolution of the alloy is characterized using electron backscattered diffraction and neutron diffraction. Taking the measured initial texture as inputs, it is shown that the model successfully captures mechanical responses, twinning, and texture evolution using a single set of hardening parameters, which are associated with the thermally activated rate law for dislocation density across strain rates. The model internally adjusts relative amounts of active deformation modes based on evolution of slip and twin resistances during the imposed loadings to predict the deformation characteristics. We observe that WE43 exhibits much higher strain-hardening rates under high strain rate deformation than under quasi-static deformation. The observation is rationalized as primarily originating from the pronounced activation of twins and especially contraction and double twins during high strain rate deformation. These twins are effective in strain hardening of the alloy through the texture and barrier hardening effects.

Experimental studies on Belleville springs use in the sliding hinge joint connection

The Sliding hinge joint (SHJ) is a low damage beam-to-column connection developed for and widely used in seismic moment-resisting steel frames (MRSFs). The asymmetric friction connection (AFC) is the SHJ's friction sliding energy dissipating component, which has also been used in other seismic resisting structural systems. In current practice, the AFC bolts are yielded at installation by the method of bolt tightening, and they are subjected to moment, shear, and axial force (MVP) interaction during stable sliding. Hence the AFC bolts tension, and as a result, SHJ elastic strength will be reduced after sliding cycles. A remedy to this post-sliding strength reduction could be installing the AFC bolts in the elastic range in conjunction with using Belleville springs (BeSs) to maintain the clamping force, but at the potential cost of deteriorating the SHJ self-centering capability. This paper describes nine real-scale SHJ's AFC component tests at quasi-static and dynamic rates of displacement controlled loading, with bolts either tightened in the elastic range using no BeSs as well as with four different configurations of BeSs which are deliberately not fully deflected at installation, to avoid the system self-centering capability deterioration and to minimize the additional imposed tension on the AFC bolts during stable sliding. It is concluded that using partially deflected BeSs with sufficient axial deformation to reach the installed bolt tension, with these being installed at both head and nut sides of the AFC bolts, will reduce the post-sliding clamping force loss, improve the self-centering capability, increase the system coefficient of friction, reduce the additional imposed tension on the AFC bolts during stable sliding due to prying actions and/or MVP interactions, and reduce the severity of the sliding surfaces' wearing.

High-speed X-ray visualization of dynamic crack initiation and propagation in bone

The initiation and propagation of physiological cracks in porcine cortical and cancellous bone under high rate loading were visualized using high-speed synchrotron X-ray phase-contrast imaging (PCI) to characterize their fracture behaviors under dynamic loading conditions. A modified Kolsky compression bar was used to apply dynamic three-point flexural loadings on notched specimens and images of the fracture processes were recorded using a synchronized high-speed synchrotron X-ray imaging set-up. Three-dimensional synchrotron X-ray tomography was conducted to examine the initial microstructure of the bone before high-rate experiments. The experimental results showed that the locations of fracture initiations were not significantly different between the two types of bone. However, the crack velocities in cortical bone were higher than in cancellous bone. Crack deflections at osteonal cement lines, a prime toughening mechanism in bone at low rates, were observed in the cortical bone under dynamic loading in this study. Fracture toughening mechanisms, such as uncracked ligament bridging and bridging in crack wake were also observed for the two types of bone. The results also revealed that the fracture toughness of cortical bone was higher than cancellous bone. The crack was deflected to some extent at osteon cement line in cortical bone instead of comparatively penetrating straight through the microstructures in cancellous bone. Statement of SignificanceFracture toughness is with great importance to study for crack risk prediction in bone. For those cracks in bone, most of them are associated with impact events, such as sport accidents. Consequently, we visualized, in real-time, the entire processes of dynamic fractures in notched cortical bone and cancellous bone specimens using synchrotron X-ray phase contrast imaging. The onset location of crack initiation was found independent on the bone type. We also found that, although the extent was diminished, crack deflections at osteon cement lines, a major toughening mechanism in transversely orientated cortical bone at quasi-static rate, were still played a role in resisting cracking in dynamically loaded specimen. These finding help researchers to understand the dynamic fracture behaviors in bone.

Experimental procedure for determination of the energy dissipation capacity of ultra-high-performance fibre-reinforced concrete under localized impact loading

Research presented in this article is aimed to investigate the ability of ultra-high-performance fibre-reinforced concrete to absorb and dissipate mechanical energy at elevated strain rate loading. Specimens made of ultra-high-performance fibre-reinforced concrete were subjected to the low-velocity impact using the new testing procedure where no fixed supports that hold the sample during the impact were applied. The fibre volume fraction of the ultra-high-performance fibre-reinforced concrete was set as the main test variable in the framework of this study and the volumetric fraction of fibres was ranging from 0.125% to 2%. A high-speed camera was used to measure velocities of the impactor and the ultra-high-performance fibre-reinforced concrete specimen before and after the impact. Consequently, the energy dissipated by the ultra-high-performance fibre-reinforced concrete specimen during the impact was calculated using a simple energy balance equation. To determine the basic material properties of ultra-high-performance fibre-reinforced concrete, quasi-static loading rate was applied and conventional methods were used. A significant difference between the values of dissipated energies for different loading rates and various fibre volumetric fractions was observed. It can be noted that the new procedure shows a reasonable approach for testing the fibre-reinforced cementitious composites under localized impact loading and is worthy of further optimization.

J–R fracture toughness of cold-worked TP316L stainless steel under seismic loading conditions

This study conducted J–R fracture toughness tests on as-received and cold-worked TP316L stainless steels (SSs) under dynamic and cyclic loading conditions to investigate the effect of seismic loads on the fracture behaviour of age-degraded materials. Additionally, tensile tests were carried out to obtain the reference mechanical properties of both materials, and to evaluate the deformation behaviours under quasi-static and dynamic loads. Cold-worked (33%) TP316L SS was used in the test to simulate irradiation-hardened TP316L SS. The J–R fracture toughness tests were conducted under monotonic load with quasi-static and dynamic displacement rates, and under cyclic load with quasi-static displacement rate at room temperature and 316 °C. The results showed that the strength and fracture resistance of TP316L SS were considerably increased and reduced by 33% cold-working, respectively; the change in strength and fracture resistance was particularly notable at 316 °C. The dynamic loading effect on the deformation and fracture behaviours was negligible for both as-received and cold-worked TP316L SSs, regardless of test temperature. Cyclic loading considerably reduced the fracture resistance of the as-received TP316L SS, but the effect of cyclic loads on the fracture behaviours was insignificant for the cold-worked TP316L SS; in particular, the cyclic loading effect was negligible at 316 °C.

Component-Level Finite Element Model and Validation for a Modern American Football Helmet

Epidemiological data and measurement of biomechanical data collected through physical experiments have contributed to the understanding of potential head injury risk in contact sports such as football. Further improvement of protective helmets requires repeatable conditions and detailed parametric studies that may be addressed in part using the Finite Element (FE) method. However, such an approach requires thorough experimentation and validation of the helmet materials and subcomponents, which previous studies do not fully address, prior to implementing these subcomponents in a full helmet model. Development of a modern football helmet FE model requires a bottom-up approach, focusing on material testing, constitutive models and subcomponent-level validation, which has not been fully addressed in the literature to date. Material samples were extracted from a modern football helmet including the helmet shell, energy-absorbing structures, comfort foam, and strap system. The subcomponents were tested across a range of quasi-static and high deformation rates relevant to football impact scenarios. FE models of the subcomponents were developed and validated, focusing on verification of material behaviour, representative loading conditions, and mesh convergence to achieve realistic responses and increase computational efficiency. Evaluation of the FE models comparing experimental with simulated responses, yielded good to excellent CORrelation and Analysis (CORA) ratings of 0.954–0.985, 0.931, 0.937–0.974, and 0.847–0.958 for the helmet shell, facemask, energy-absorbing structures, and comfort pads, respectively. The resulting validated subcomponent-level models provide an important foundation for integration into a full helmet model to ultimately optimize performance and reduce head injury.

Fracture toughness measurement without force data – Application to high rate DCB on CFRP

The measurement of the fracture toughness of fiber reinforced composites at high rates of loading is still, despite years of research, not well established. This can be related to challenges in applying appropriate high rate loading on the specimen, accurately measuring the load, and in-situ determination of the crack length. In this work these challenges are addressed by using a direct wedge-on-specimen type loading of a double cantilever beam (DCB) specimen, high resolution optical deformation tracking, and a beam theory based analysis of the specimen deflection and crack length. This approach results in symmetric mode I opening of the crack and a robust analytical determination of the fracture toughness without the need to measure the external forces acting on the specimen nor to visually estimate the crack length. Tests carried out on carbon fiber reinforced epoxy composite at quasi-static and high rates (relative velocity up to 15 m/s) show the validity of the approach.

Fasteners in Steel Fiber Reinforced Concrete Subjected to Increased Loading Rates

Increased loading rates on fasteners may be caused by high ground accelerations as a consequence of e.g., nuclear explosions, earthquakes or car collisions. It was concluded by Hoehler et al. (2006) that fasteners under rapid loading rates show an increased ultimate resistance in the concrete dominant failure modes or the ultimate resistance is at least as large as under quasi-static loading. Due to the increased demand on using fasteners in steel fiber reinforced concrete (SFRC), it is intended to show how the ultimate concrete cone capacity of fasteners changes under higher than quasi-static loading rate in normal plain concrete (PC) and in SFRC. This paper presents the results of an extensive experimental program carried out on single fasteners loaded in tension in normal plain concrete and in SFRC. The test series were conducted using a servo-hydraulic loading cylinder. The tests were performed in displacement control with a programmed ramp speed of 1, 100, 1000, and 3500 mm/min. This corresponded to calculated initial loading rates ranging between 0.4 and 1600 kN/s. The results of the tension tests clearly show that the rate-dependent behavior of fasteners in SFRC with 30 and 50 kg/m3 hooked-end-type fibers fits well to the previously reported rate-dependent concrete cone behavior in normal plain concrete. Additionally, a positive influence of the fibers on the concrete cone capacity is clearly visible.

Influence of quasi-static loading rates on crushable granular materials: A DEM analysis

Does granular material show strain rate dependent response, especially with quasi-static loading condition? The answer is both yes and no since it depends on various factors like particle shape, size and crushability. In the present study, a micromechanical analysis is carried out using discrete element modelling (DEM) to explore the effects of variation in the loading rates, within/near the quasi-static regime, on the stress-strain response of crushable and non-crushable granular assemblies. The study considers monotonic loading at two different strain rates and a sudden strain rate shift condition. The numerical simulation of one-dimensional (1D) compression shows quasi-static loading, which usually produces rate-independent response, can demonstrate rate-dependent features during particle crushing. The variation in the contact force distribution within the granular assembly at different loading rates, dictates the stress response and the crushing events. Relatively low strain rate compression favors homogeneous crushing involving a large number of particles that consequently reduces the strength via fragments rearrangement. Conversely, high strain rate promotes localized crushing within fewer particles, and thus strain hardening is observed. Sudden strain rate shift within the granular assembly creates a discontinuous velocity profile that hampers the crushing events.

Influence of kenaf fabric on the tensile performance of environmentally sustainable fibre metal laminates

Towards the use of environment friendly materials, the recent trend has inclined to the natural based resources in a wide variety of applications. Fibre metal laminates are the contemporary materials used in aerospace industry due to the excellent mechanical behaviour compared to conventional metallic alloys. In this study, the effects of kenaf fabric layers, fibre orientations and chemical treatment on the tensile responses of thermoplastic fibre metal laminates were investigated. The laminates were formed based on plain weave kenaf fabric, polypropylene and annealed aluminium 6061 through the hot press compression method. The tensile test was performed at a quasi-static rate of loading with reference to ASTM E8. Experimental results revealed that the number of kenaf fabric has a major contribution to the tensile strength and modulus of the laminates. For untreated laminates, it was noticed that the increase in the kenaf fabric layers deteriorates the tensile strength and modulus. For treated laminates, the encapsulation of two layers of kenaf fabric exhibited the highest tensile properties. Furthermore, fibre metal laminates with a fibre orientation of 0°/90° exhibited higher tensile strength and modulus compared to fibre orientation of ±45°. However, higher elongation was observed for the laminates with a fibre orientation of ±45° due to the scissoring effect. Overall, the treated laminates showed higher tensile strength and modulus than untreated laminates.