Shear Impact Loading Research Articles

A comparative study of constitutive models for EPS foam under combined compression and shear impact loading for helmet applications

Virtual testing of helmets using finite element (FE) analysis can be a valuable tool during product development. Still, its usefulness is limited by the quality of the constitutive model of the energy-absorbing material, usually foam. Built-in constitutive models in commercial FE software are developed for traditional linear compression loading. However, modern oblique test methods load the foam in combined compression and shear. Therefore, we aim to evaluate to what extent built-in constitutive models in commercial FE software can represent Expanded Polystyrene (EPS) foam during combined compression and shear loading (CCSL). EPS foam is tested experimentally in a newly developed test rig for CCSL (V-test). The response is compared against the simulation using three different constitutive models available in LS-DYNA (M83, M126, and M181). The models are assessed by their ability to capture the correct response, focusing on how well the continuum models can capture the phenomenological events seen in the experiments. The results show that the models perform well in compression, as expected. However, we point out limitations in the shear response and significant limitations in the unloading response, both important for oblique helmet testing. Due to these limitations, we conclude that the existing models are inadequate for accurately simulating oblique helmet impacts. There is a clear need to develop and implement new constitutive models focused on capturing CCSL including the unloading. Additionally, frictional sliding was found to substantially influence the measured response in the V-test method. Minimizing interface sliding is therefore critical for isolating the material behavior.

Numerical simulation of the damage and ignition responses of high explosives under low-velocity impact using the SPH method

The damage evolution and ignition mechanism of high explosives are of great importance in assessing the safety of munitions and guiding the design of munitions. In this study, the smoothed particle hydrodynamics (SPH) method is combined with a viscoelastic–viscoplastic-damage constitutive model and a hot spot model to explore the damage and ignition responses of high explosives under low-velocity impact. In particular, the sub-particle method is developed in the SPH method to combine the macroscopic constitutive model with the mesoscopic hot spot model. First, the damage evolution of a compressed plate containing a cavity and the ignition response of a single particle at a given pressure and strain rate are studied separately, and the simulation results are validated by experimental results and existing finite element method simulations. Subsequently, the impact shear and crack extrusion tests of high explosives with complex stress states are explored, respectively. For typical pressed PBX under impact-shear loading, a large damage region is formed in the high explosives due to the tensile stress formed by the meeting of rarefaction waves, and the initial ignition region is mainly located in the region where the outer edge of the rod is in contact with the high explosives and extends in a circular shape to the inside of the explosives. For typical pressed PBX under crack extruded loading, the damage region is mainly concentrated in the materials squeezed into the crack, and the initial ignition region is mainly located around the crack and gradually extends above the crack. The results indicate that the proposed SPH method is capable of modeling the damage and ignition responses of high explosives under complex stress states.

Elastoplastic stress wave propagation in functionally graded material due to combined compression and shear

In the present paper, an analytical model for the propagation of stress waves in a functionally graded half-space subjected to combined compression and shear impact loading is established. The functionally graded materials (FGMs) based on the elastic–plastic model (the Tamura–Tomota–Ozowa model) are assumed to be continuously graded according to a power-law function of the volume fractions of the constituents. Based on generalized characteristics theory, the characteristic wave speeds were obtained and analyzed. The finite difference method was implemented to discretize the governing equations. Typical numerical examples for FGMs with positive and negative gradients are presented. The numerical examples reveal that the FGMs have the function of managing stress waves. Unlike traditional elastoplastic materials, the wave structures of FGMs will also change depending on such factors as the initial stress state, the amplitude of the loading, and the gradient distribution of the material.

A testing device to investigate the properties of strain-hardening, cement-based composites (SHCC) under impact shear loading

Strain-hardening, cement-based composites (SHCC) are a novel class of fiber-reinforced concretes which exhibit high tensile strain capacity and crack control prior to failure localization, making them suitable for application as strengthening layers or as main materials for construction elements exposed to severe loading and environmental conditions. As opposed to their tensile properties, the shear performance of SHCC has been only scarcely investigated. In the context of structural strengthening against dynamic actions such as impact loading, the paper at hand describes the development, implementation, and testing of a shear testing setup for ductile cementitious composites. The development of the testing setup had as its target its integration in a gravity-driven Split-Hopkinson tension bar (SHTB) and required both finite element modeling and experimental testing. The numerical modeling aimed at a detailed parameter study of the device geometry, boundary conditions, and notch configuration of the material specimens as well. The experimental program implied both quasi-static and impact shear experiments on normal-strength SHCC made with ultrahigh-modulus polyethylene (UHMWPE) fibers. Both the numerical and experimental analyses demonstrated the inapplicability of one-dimensional wave analysis in deriving specimen shear response. This was solved by applying high-speed optical measurements with subsequent digital image correlation (DIC), which also allowed the accurate evaluation of the fracture modes related to load history. The study highlighted the pronounced influence of loading and boundary conditions on the specimens’ response and demonstrated the necessity of complementary numerical analyses to derive the constitutive relationships of SHCC. Furthermore, it serves as basis for further device optimization in respect of structural and inertial effects.

Simulation of impact failure of tubular samples made of composite material, depending on the loading rate

In this paper, a model that takes into account the dependence of strength properties on the damage rate is considered for modelling of the impact failure of composite materials. The constants of the material model are determined on the basis of experimental diagrams to compression and shear impact loading of unidirectional composite, which exhibit a nonlinear dependence on the strain rate. The proposed model is implemented to the Abaqus finite element modeling software for the case of a three-dimensional stress state. As an example of numerical modeling, we consider tubular composite specimens made of carbon fiber with an epoxy matrix and layers of different orientations, which are commonly used for determining of characteristics of impact energy absorption. Diagrams of impact loading of the considered tubular specimens are obtained. The influence of the chamfer (taper of the cross-section) on the edge of a tubular specimen on the impact loading diagram at the initial stage of the process, which serves as the initiator of crushing, is studied. The proposed approach allows us to estimate the magnitude of the peak of the amplitude associated with the crushing of the chamfer. In addition, at the initial stage of loading, maximum strain rates occur, which entails the hardening of the material, also expressed in the loading diagram as an increase in the amplitude. If the analysis neglects the effects associated with the strain hardening of the material and the geometry of the chamfer, the result may be expressed in an underestimation of the reaction, especially at the initial stage of the process. The absence of the described effects in the model of composite structures may lead to significantly incorrect results with complete failure with zero reaction. The developed approach is effective in the design and testing of damping elements made of composite material with properties that are sensitive to the loading rate.

Transient behavior of an orthotropic layer with imperfect FGM coating containing multiple interfacial and embedded cracks under anti-plane shear impact load

This paper investigates the transient response of an orthotropic strip with functionally graded (FG) coating weakened by multiple embedded and interfacial cracks. The first part of this paper is concerned with the dynamic response of embedded cracks in the orthotropic substrate with imperfect FG coating. In the second part, the solution of interfacial crack is obtained analytically to extract the dynamic stress intensity factors (DSIFs). In the third part, the proposed method is developed to examine the dynamic fracture behavior of coating–substrate system with an orthotropic FGM coating bonded to an orthotropic substrate through a layer of a bond-coat. In all parts, Laplace and Fourier transforms are used to reduce the problems to a set of singular integral equations with Cauchy kernels which are solved numerically in the Laplace transform domain. The dynamic stress intensity factors are obtained by the numerical Laplace inversion technique. Several examples are solved to obtain DSIFs with various crack lengths and the spring constant of imperfect bonding and material properties of the layers.

Intersonic shear crack propagation using peridynamic theory

Dynamic crack propagation of mode-II cracks is simulated using bond-based Peridynamic Theory (PD) implemented in finite element analysis software ABAQUS. The specimen is a bonded homogeneous Homalite plate with a pre-notch that is subjected to impact shear loading simulating the experiments of Rosakis et al. (1999). The PD bonds at the bonding interface are utilized with a scalar critical stretch value that corresponds to mode-II fracture toughness of the interface. The crack initiation and propagation are naturally captured in the bond-based PD simulations by modifying the original prototype microelastic brittle law formulation introduced by Silling and Askari (2005). Impact loading is introduced at the specimen as a pulse speed field boundary condition. Using bond-based PD, sub-Rayleigh and intersonic regimes of crack growth are obtained as a function of fracture toughness ( $$G_{II}$$ ) and impact speed ( $$V_i$$ ) values. The intersonic crack growth is discerned from the sub-Rayleigh crack growth by the existence of shear Mach waves in the particle velocity magnitude contours. For critical values of $$G_{II}$$ and $$V_i$$ , a crack growing at a speed just below the Rayleigh wave speed is observed to transition to an intersonic speed with a Burridge-Andrews mechanism. The sustained intersonic crack tip speed is found to be between $$1.57c_S$$ ( $$c_S$$ is the shear wave speed) and $$c_D$$ ( $$c_D$$ is the dilatational wave speed). For a reduced impact pulse duration, an intersonic crack is found to approach the theoretical value of $$\sqrt{2}c_S$$ , which, however is not maintained. The results are in qualitative agreement with the experiments of Rosakis et al. (1999) and previous simulations in the literature.

Transient response of collinear Griffith cracks in a functionally graded strip bonded between dissimilar elastic strips under shear impact loading

This article analyses the interaction between a central and two symmetrically placed collinear Griffith cracks subjected to transient response under anti-plane shear impact loading. The cracks are situated in a strip constituted by functionally graded material (FGM) bonded between two dissimilar elastic strips of equal thickness. The material properties of FGM are assumed to vary exponentially as a function of thickness. Applying integral transforms, the boundary value problem reduces to a system of singular integral equations in the Laplace transformed domain. These equations are solved numerically using the Lobatto-Chebyshev collocation quadrature approach. The inverse Laplace transform is used to find the approximate expressions of dynamic stress intensity factors (DSIFs). The striking feature of the article is the study of phenomenal changes of shielding and amplification through dynamic stress magnification factors (DSMFs) at the tips of the cracks under the sudden impact loading applied at the upper material surface. The effects of impact load applied at different surfaces, positions of cracks’ axis and the thickness of the strips of the composite material on the possibilities of cracks’ arrest are depicted graphically for different particular cases.

A novel evaluation of shock absorption and adhesive strength under shear impact loading

ABSTRACT The authors study shock absorption characteristics and their measurement methods because test standards and specifications for shock absorbing adhesives are not clearly established. Especially, microscale shock absorbing adhesive characteristics are important for mechanical properties of small-sized mobile electronics with slim, bezel-less design. For this purpose, a piezoelectric force sensor is utilized to evaluate impact response of various adhesives under ball drop impact due to high-frequency data acquisition. Next, the evaluated impact responses are compared with dynamic mechanical analysis results to confirm the viscoelastic material behavior of adhesives. In addition, the impact response is proportionally correlated with the damping factor. In order to characterize both shock absorption and adhesive strength simultaneously, a novel test apparatus for shear impact is devised based on the previous test. The correlation between two mechanical properties is determined by analyzing the change of the impact force transmitted through the adhesive. The degradation of the adhesion strength is described by the damage model, which estimates its change before detachment. The proposed experimental mechanics not only enables a concurrent evaluation of adhesion strength and shock absorption but also assesses required adhesive materials for delicate electronic components.

Mechanical behavior of 3D GFRP composite with pure and treated shear thickening fluid matrix subject to quasi-static puncture and shear impact loading

In this study, a new low-velocity shear impact test was introduced to carefully investigate the resistance of 3D E-glass fiber reinforced polymer composites with shear thickening fluid matrix. The shear thickening fluids were prepared by dispersing silica nano-particles in polyethylene glycol. Pure shear thickening fluid was modified by treating the silica surface with (3-Aminopropyl) triethoxysilane. Despite the low-velocity shear impact test, various experimental tests such as yarn pull-out, quasi-static puncture, flexibility and thickness tests were carried out to study the mechanical behavior of the composites. Results revealed the treated shear thickening fluid up to 60 wt% improves the performance of the impregnated samples against the yarn pull-out and puncture tests by 353% and 45%, respectively, and their shear impact resistance by 130% compared to the neat cases without noticeably affecting the fabric flexibility.

Parametric study of a fibrous energy absorbing material under impact shear loading

A comprehensive experimental impact characterization study of novel impact energy absorbing (IEA) materials under impact shear loading is conducted. Electro-flocking process is employed to fabricate the novel fiber based padding materials, also known as flocked energy absorbing materials (FEAM). FEAM IEA panels are prepared by flocking 1–3 mm long, 6–60 denier nylon fibers onto a planar polyester fabric sheet. The impact energy absorption under combined pre-compression loading and shear impact loading is investigated using a custom built guided weight drop tower along with a specially designed pre-compression and shear loading fixture for this study. A parametric study is performed where the effect of fiber material properties such as flock fiber length, diameter and flock density (number of flock fibers per area) on IEA is investigated and they are later compared with that of Vinyl Nitrile (VN) foam materials. Padding material based on FEAM configurations showed remarkable improvement when compared directly to VN foam with a 135% increase in shear strain energy density for the high impact velocity loading condition. Additionally, for low velocity impact conditions, the FEAM based padding materials out performed with a 49% increase in shear strain energy density as compared to VN foam.

Dynamic stress intensity factors of an interfacial crack in orthotropic elastic strips under impact loading conditions

AbstractThe present article deals with the investigation of elasto‐dynamic response of a finite crack under normal and shear impact loading situated at the interface of two semi‐infinite orthotropic strips. Laplace and Fourier Integral transforms are employed to reduce the transient problem to the solution of a pair of dual integral equations in the Laplace transform plane which are solved using iterations in the low frequency domain. The analytical expressions of stress intensity factors of the crack at the interface problem are found. To determine time dependence of the parameters, these equations are inverted to yield the dynamic stress intensity factors for some fiber‐reinforced orthotropic composite materials using Bellman method and the method given by H. Dubner and J. Abate. The results are depicted through graphs for different particular cases.

Dynamic Experiments using Simultaneous Compression and Shear Loading

Material characterization at high strain rates under simultaneous compression and shear loading has been a challenge due to the differing normal and shear wave speeds. An experimental technique utilizing the compression Kolsky bar apparatus was developed to apply dynamic compression and shear loading on a specimen nearly simultaneously. Synchronization between the compression and shear loading was realized by generating the torsion wave near the specimen which minimizes the time difference between the arrival of the compression and torsion waves. This modified Kolsky bar makes it possible to characterize the dynamic response of a material to combined compression and shear impact loading. This method can also be applied to study dynamic friction behavior across an interface under controlled loading conditions. The feasibility of this method is demonstrated in the dynamic characterization of a simulant polymer bonded explosive material.

Mechanism of shear attenuation near the interface under combined compression and shear impact loading

We investigate the compressional/shear coupling plastic wave propagation characteristics analytically for ideal elastic–plastic materials in both stress and particle velocity spaces, focusing on the shear wave attenuation near the interface occurring in pressure–shear plate impact experiments. The results show that the shear attenuation is strongly associated with the wave propagation characteristics of the coupling waves. In the stress space, as the shear stress increases, an adjustment of the stress components is observed and the final stress state along the wave path is a combined pure shear- and hydrostatic pressure-state. In the particle velocity space, the wave structures with different loading and maximal transverse particle velocity are obtained. The maximal transverse particle velocity varies with the longitudinal velocity and forms a boundary line. Once the loading transverse velocity exceeds this line, a transverse particle velocity discontinuity occurs at the impact interface. If the bonding strength is sufficiently high, there will be a shear band in the target in the extreme vicinity of the interface.

Impact shear damage characterizations of 3D braided composite with X-ray micro-computed tomography and numerical methodologies

This paper presents the impact shear fracture mechanisms of 3D braided composite observed from computed tomography (CT) and the comparisons with finite element analyses (FEA). The effects of braiding parameters on the damage modes have been analyzed from micro-CT and FEA. It revealed that there are multiple damage modes of fiber tows fracture, debonding, resin cracks and inter-yarn delaminations under impact shear loading. The failure mode mainly depends on the braiding structural parameters, which in return determines the energy absorption capacity. A meso-structure geometrical model based on braided preform structure was developed to calculate the stress distribution and to simulate the shear damage modes. The failure modes from FEA were compared with those obtained from the micro-CT. Both the micro-CT and FEA observations capture the impact shear damage morphologies and unveil the energy absorption mechanisms.

Impact shear resistance of double skin profiled composite wall

This paper presents the behavior of a new form of composite walling system consisting of two skins of profiled steel sheeting and an infill of concrete subjected to in-plane impact loading. Composite wall specimens with overall dimensions of 1626mm high by 720mm wide were tested under impact shear loading in two phases, namely Phase I and Phase II (in addition to ones tested under in-plane monotonic shear). In Phase I, impact energy of the projectile was kept low intentionally to capture dynamic characteristics of wall. In Phase II, the impact test was performed with maximum speed of the projectile, which the impact apparatus could produce. The performance of composite walls was judged based on the development of acceleration and top displacement during impact as well as post-impact shear-displacement response, strength/stiffness, energy absorbing capacity, stress development and failure modes. The post-impact shear strength of walls was found to be not reduced (compared to control wall tested under static monotonic loading without impact) after the application of impact energy. The stiffness degradation of the wall after impact was around 8% compared to the control wall. This was an indication of better strength/stiffness retaining capacity of the walls after subjected to impact. Theoretically predicted maximum displacement at the top of the wall at impact was also found to be in good agreement with those obtained from experiments. This research confirmed the suitability of proposed profiled double skin composite wall (DSCW) to be used as impact shear resisting element in framed buildings.

USE OF MECHANOCHEMICAL ACTIVATION TO CONTROL RHEOLOGICAL PROPERTIES OF MOULDING PASTES FOR CATALYSTS AND SORBENTS EXTRUSION

For citation:Svyatenko N., Prokof’ev V.Yu., Gordina N.E. Use of mechanochemical activation to control rheological properties of moulding pastes for catalysts and sorbents extrusion. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 102-107.The influence humidity, grinding and mechanical activation of the solid phase on the rheological properties of the molding paste for extrusion of catalysts and sorbents was studied. The following parameters of the molding pastes were investigated, namely the coagulation structure strength, the flow index, the maximum plastic viscosity, the critical shear stress, plasticity, the r (stuelaxation period), the ratio of deformations. In order to characterize the degree of mechanochemical activation, the dimension of the coherent scattering region and the microdeformations value were used. Increasing the degree of mechanochemical activation of the solid phase was shown to allow controlling the properties of molding pastes in a more wide range. In the technology of extruded catalysts and sorbents, the mills-activators with the impact-shear loading are proposed to use. The mills with an average value of power density (up to 6 kW/kg) were recommended.

Finite element modeling of impact shear resistance of double skin composite wall

This paper presents the finite element (FE) modeling of a new form of composite walling system consisting of two skins of profiled steel sheeting and an infill of concrete subjected to in-plane impact loading. Composite wall specimen tested under impact shear loading in two phases, namely Phase I and Phase II was used to develop the FE model. In Phase I, the impact test was performed repeatedly keeping the impact energy of the projectile low intentionally to capture dynamic characteristics of the wall. In Phase II, the impact test was performed once with high impact energy (using maximum projectile speed the apparatus could produce). The developed FE model was used to simulate acceleration/displacement at the top of the wall during impact, impact energy dissipation, fundamental period, stress-strain development/concentration, shear strain/rate evolution, impact duration and bounce back impact time. The FE model predicted values/responses were found to be in good agreement with those obtained from experiments. Extensive parametric studies were conducted to study the influence of varying geometric, material and sheet-concrete interface parameters governing the composite wall performance under impact loading using the developed FE model.

The Co-Grinding of Z/Cao/Al(OH)3 (Z = ZnO Or Zn4CO3(OH)6) Powder Compositions as Technique for Preparation of Sorbents

The co-grinding processes for ZnO/CaO/Al(OH)3 and Zn4CO3(OH)6/CaO/Al(OH)3 powder compositions in a vibratory mill with an impact-shear loading were studied. The solid phase was investigated by the methods of X-ray diffraction, IR spectroscopy, scanning electron microscopy, synchronous thermal analysis and other methods. It was found that the formation of new Ca(Zn2(OH)6) phase takes place only in the ZnO-containing mixtures. The detected calcium hexahydroxodizincate dehydrate crystals had a prismatic shape. The experimental data showed also that the co-activation process is accompanied by the hydration of the particle surface due to the alignment of the basic properties of the initial compositions. The amount of gibbsite in the composition influences the changes in a crystal structure. The co-grinding of both compositions allows one to obtain the pellets which keep the mechanical durability after the saturation with HCl vapors. It was shown that the compositions with the basic zinc carbonate are characterized by the higher absorption capacity for the HCl vapors.

Mechanical Properties of Lead-Free Solder Joints Under High-Speed Shear Impact Loading

In this study we expanded on recently reported research by using a modified miniature Charpy impact-testing system to investigate the shear deformation behavior of Sn–3.0Ag–0.5Cu lead-free solder joints at high strain rates ranging from 1.1 × 103 s−1 to 5.5 × 103 s−1. The experimental results revealed that the maximum shear strength of the solder joint decreased with increasing load speed in the ranges tested in this study. For solder joints tested at a shear speed exceeding 1 m/s, corresponding to an approximate strain rate that exceeds 1950 s−1, the brittle fracture mode is the main failure mode, whereas lower strain rates result in a ductile-to-brittle transition in the fracture surfaces of solder joints. In addition, the mode II stress intensity factor (KII) used to evaluate the fracture toughness (KC) of an interfacial intermetallic compound layer between Sn–3.0Ag–0.5Cu solder and the toughness of copper substrate was found to decrease from 1.63 MPa m0.5 to 0.97 MPa m0.5 in the speed range tested here.