Strain Rate Impact Research Articles

Interfacial kinematics and governing mechanisms under the influence of high strain rate impact conditions: Numerical computations of experimental observations

This paper investigates the complex interfacial kinematics and governing mechanisms during high speed impact conditions. A robust numerical modelling technique using Eulerian simulations are used to explain the material response of the interface subjected to a high strain rate collision during a magnetic pulse welding. The capability of this model is demonstrated using the predictions of interfacial kinematics and revealing the governing mechanical behaviours. Numerical predictions of wave formation resulted with the upward or downward jetting and complex interfacial mixing governed by wake and vortex instabilities corroborate the experimental observations. Moreover, the prediction of the material ejection during the simulation explains the experimentally observed deposited particles outside the welded region. Formations of internal cavities along the interface is also closely resemble the resulted confined heating at the vicinity of the interface appeared from those wake and vortex instabilities. These results are key features of this simulation that also explains the potential mechanisms in the defects formation at the interface. These results indicate that the Eulerian computation not only has the advantage of predicting the governing mechanisms, but also it offers a non-destructive approach to identify the interfacial defects in an impact welded joint.

Simulation and experimental investigation of strain rate impact on martensitic transformation in 304L steel through dome test

Abstract

Quasi-static characterisation and impact testing of auxetic foam for sports safety applications

This study compared low strain rate material properties and impact force attenuation of auxetic foam and the conventional open-cell polyurethane counterpart. This furthers our knowledge with regards to how best to apply these highly conformable and breathable auxetic foams to protective sports equipment. Cubes of auxetic foam measuring 150 × 150 × 150 mm were fabricated using a thermo–mechanical conversion process. Quasi-static compression confirmed the converted foam to be auxetic, prior to being sliced into 20 mm thick cuboid samples for further testing. Density, Poisson’s ratio and the stress–strain curve were all found to be dependent on the position of each cuboid from within the cube. Impact tests with a hemispherical drop hammer were performed for energies up to 6 J, on foams covered with a polypropylene sheet between 1 and 2 mm thick. Auxetic samples reduced peak force by ∼10 times in comparison to the conventional foam. This work has shown further potential for auxetic foam to be applied to protective equipment, while identifying that improved fabrication methods are required.

Microstructural evolution associated with shear location of AISI 52100 under high strain rate loading

The microstructure evolution of adiabatic shear bands (ASBs) in AISI 52100 produced under high strain rate impact loading was investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A full view of the shear band formation and development was presented. The results reveal that no strain hardening effect occurred in the AISI 52100 under the dynamic loading. Two distinct regions of the ASBs and the transition region were observed. Driven by the high shear deformation and assisted by a thermal softening effect, the formation of ASBs started in the core region under the dominant mechanism of dynamic recrystallization. It is followed by the formation of neighbouring region under the co-action of both dynamic recovery and dynamic recrystallization. Then the transition region formed which was controlled by dynamic recovery. The core region of ASBs was consisted of subgrains and fine equiaxed grains. The grains were refined either through partitioning and breaking down the elongated subgrains by entangled dislocations clusters or through splitting and rotating the elongated subgrains into small grains under a synergistic effect of shearing and twisting. The amount and size of cementites were greatly reduced in ASBs due to cementite dissolution induced by large plastic deformation and dynamic recrystallization.

Strain and Rate-Dependent Diffuse Axonal Injury of 3D Neuron Cultures Under Compression

In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for diffuse axonal injury. This information is critically important for the development of mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and strain rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude determines the time of neuronal death, strain rate governs the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Similarly important, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, does not occur under compression.

Failure processes governing high-rate impact resistance of epoxy resins filled with core–shell rubber nanoparticles

Epoxy resins are classically toughened by rubber additives, but the effectiveness of rubber toughening tends to diminish with increasing strain rate, decreasing temperature, and decreasing matrix ductility. In this study, we demonstrate that low loadings of 100–200-nm core–shell rubber (CSR) particulate additives can improve high strain rate (104–105 s−1) impact resistance by nearly 200 % for epoxy resins with glass transition temperatures T g in a range between 60 and 110 °C, without large reductions in T g or stiffness. In addition, CSR additives improve low-temperature impact resistance of the epoxies down to 0 °C. Size and surface chemistry of the CSR particles influence the ballistic response, with 200-nm diameter, weakly bound, and poorly dispersed CSR particles providing the greatest toughening performance at low filler loadings and high rates. Impact resistance for a systematic series of CSR-modified epoxies covers a transition from brittle to tough behavior, where the failure mechanism changes with effective fracture resistance. For brittle resins, failure is dominated by initiation of Hertzian cone fracture which depends strongly on fracture toughness K IC, while for tough resins, failure is dominated by plastic yield at the impact site and is independent of fracture toughness above a minimum K IC value of approximately 1.2–1.5 MPa m1/2. Interestingly, quasistatic mechanical properties are reasonably effective qualitative predictors of high-rate impact resistance, suggesting that the toughening mechanisms of CSR particles are similar over the rates studied here. The insights gained from this study are valuable for design of next generation adhesives, polymers, and polymer composite matrices for lightweight protective applications.

Stress-Strain Behavior of Nylon-Carbon Composite Subjected to High Strain Rate Impact Loading

The aim of this study is to investigate the dynamic stress-strain relation for the hybrid composite (nylon +carbon). Three groups of specimens are used with different number of carbon layers. The specimens were subjected to high velocity impact with different strain rates. SHPB (split Hopkinson pressure bar) is used in this investigation. The results show that, the stress-strain relation various with the strain rate. The maximum stress and strain are proportion directly with the strain rate. Also, the results revealed that, as the number of carbon layer increased, the maximum strain decreased.

Microstructural simulation of adiabatic shear band formation in AISI 4340 steel using Voronoi Tessellation

Using the stress strain response data obtained from an experimental investigation carried out by the first author (Polyzois, 2014), a finite element model was developed in Matlab and explicit FEA software ANSYS and LSDYNA to simulate Adiabatic Shear Band (ASB) formation in AISI 4340 steel on the microstructural level under high strain rate impact. This FEA model uses the Voronoi Tessellation to generate geometry simulating the microstructure of heat treated AISI 4340 steel in a 2D axi-symmetric cross-section based on the prior austenite grain size and 2D geometric orientation of martensitic lath blocks. It also incorporates the microstructural material inhomogeneity between the grains and the grain boundaries. The model was discretized using the meshless Smooth Particle Hydrodynamics (SPH) method and utilizes the Johnson–Cook plasticity model parameters for various heat treatments of the steel as well as a rupture failure criterion. The model provides a good representation of the kinematics of ASB formation based on grain refinement showing a progressive reorientation and elongation of the grains in the direction of shear in 2D. Severe strain localization and ASB formation were shown to nucleate at the grain boundaries of the elongated grains, creating micro-voids, which grew and propagated as micro-cracks through the grains, separating them into smaller sizes. Under continued deformation, the grains continued to elongate and refine. Final refined grain size within the band is represented by the size of the smallest cluster of intact SPH particles.

The Effect of Thicknesses on Impact Damage Advanced Composite Material for Aircraft Application

Investigation of impact damage on advanced composite materials of Carbon Fiber Reinforced Epoxy (CFRE) composites and Glass Fiber Reinforced Epoxy (GFRE) composites under high strain rate impact load have been conducted in the present study. Four types of GFRE plates were studied after being impacted with various thicknesses and fixed impact parameters. Results of the present experiments were characterized by the comparison of damage zone among CFRE/GFRE, GFRE with honeycomb core and GFRE without honeycomb core. The result suggests that CFRE is the better structure than GFRE under low velocity impact loads. Higher energy needed to damage the surface of GFRE with core compared to GFRE without core plates.

Development of a lower extremity model for high strain rate impact loading

In recent military conflicts, the incidence of underbody blasts has led to severe injuries, specifically in the lower extremities. The development of a lower extremity model may lead to a better understanding of injury patterns and mechanisms. A computational finite element model of the lower extremity was developed based on geometry made available in an anatomical repository. The portion of the extremity model below the knee was used in initial comparisons between simulations and experimental data. Impact was applied via a loading plate with a vertical velocity of 5 m/s, 10 m/s, and 12 m/s. Resultant axial force was compared to experimental data. Results of these simulations fall within the range of available experimental data, which gives confidence that this model represents advancement in lower extremity modelling capabilities. Bone fracture has also been modelled and shows consistency with injuries typical of underbody blast scenarios.

Tensile Behavior of Polyetheretherketone over a Wide Range of Strain Rates

Polyetheretherketone (PEEK) is used in several engineering applications where it has to bear impact loads. Nevertheless, the tensile behavior has only been studied in the quasi-static range of loading rates. To address the lack of data in the impact strain rate range, the tensile mechanical behavior of PEEK is investigated at room temperature over a large range of strain rates (from 0.001 to 1000/s). The macroscopic volume change is studied under uniaxial tension using digital image correlation (DIC) method, showing a significant dilatation that reaches 16% at a logarithmic axial strain of 40%. The true stress-strain behavior is therefore established based on the measured volume change. Elsewhere, the yield stress shows a significant sensitivity to strain rate. Besides, a new constitutive equation is proposed to take into account the increase in strain rate sensitivity at high strain rates. It assumes an apparent activation volume which decreases as the strain rate increases. The new constitutive equation gives similar results when compared to the Ree-Eyring equation. However, only three material constants are to be identified and are physically interpreted.

The Effect of High-Strain Rate on Friction and Wear Behaviors of AZ31 Magnesium Alloy

In this study, wear behaviour of AZ31 magnesium alloy shocked by Hopkinson pressure bar was measured, the microstructure morphology was observed and the effect of high strain rate impact on wear resistance and wear mechanism of the alloy were analysed. The results show that: the wear property of AZ31 is improved by the impacted in a reasonable strain rate, but when the strain rate is high enough, it will cause the alloy inactivation. The wear mechanism of the alloy is main grain-abrasion wear, accompanied with the other form of wear, and there will be adhesive wear with the increase of the strain rate.

Tensile deformation behavior and microstructure evolution of Ni-based superalloy 617

The mechanisms of deformation were investigated in a nickel-based alloy (Inconel 617) of interest for the Intermediate Heat Exchanger (IHX) for the very high temperature reactor (VHTR). Tensile tests at 25°C, 600°C, 800°C, and 950°C were conducted in air at different strain rates. The tests were followed by electron microscopy analysis (including FE-SEM, TEM, EDX). The tensile property measurements and the metallographic examination of tested specimens allowed relating the deformation behavior with the microstructural changes in the material. The temperature and strain rate impact on the properties was assessed. The results and microstructure observations were discussed in terms of serrated flow associated with dynamic strain ageing, precipitate evolution, and softening processes due to dynamic recrystallization.

Investigation on Micro-Structure Evolution of Mg-12Gd-3Y-0.5Zr Magnesium Alloy under High Velocity Impact

Cubic-shaped specimens and hat-shaped specimens were used to investigate ASBs formed in Mg-12Gd-3Y-0.5Zr magnesium alloy under different initial strain rate impact. It shows that no adiabatic shear bands (ASBs) is observed in micro-structure of cubic-shaped specimens by scanning electron microscope (SEM) , but obvious ASBs can be observed in hat-shaped specimens. Johnson-Cook model based on thermoviscoplasticity constitutive relation was used to simulate internal stress distribution and fracture mode, and it indicated that the result of failure analysis from specimens under high velocity impact tests was the same as that obtained by computer simulation.

A Study on Reduction of Friction in Impact Compressive Test Based on the Split Hopkinson Pressure Bar Method by Using a Hollow Specimen

The split Hopkinson pressure bar (SHPB) technique is widely-used to describe the impact compressive behavior of different materials including metals. During the impact test, the specimen deforms in a wide range of impact strain rate from 102 to 104 s-1. It is a reason why the method is studied for many years even though the structure of the apparatus based on the SHPB is simple. Actually, the cylindrical specimens are widely used for a compressive test and it is clearly seen that stress measured by the test includes the increment of stress (an error) derived by friction effect between a specimen and pressure bars. Therefore, it is important that the measured stress should indicate similar value as the proper stress of the material by reducing friction effect during not only quasi-static but also the impact test. Various attempts to reduce a friction effect in past have been conducted. A method to reduce friction effect is in general a use of lubricants. However, it is ineffective because it can be considered that this method contributes to an attenuation of the stress wave for obtaining the stress-strain curve under impact loading. Thus, rise time of waves obtained by the experiment becomes longer compared with a case not to use lubricants. Recently, a study can be found using a ring specimen, however, the determined thickness of the specimen is quite thin and it can be considered that a buckling effect cannot be vanished. In this study, a use of hollow specimen is suggested to solve the problem related to reduce the friction effect by decreasing a contact area between a specimen and pressure bars instead of a cylindrical specimen. The compressive experiments at various strain rates are conducted by using a hollow specimen.

Modelling and testing of elastomer impact deformation under high strain rates

Elastomers are frequently used in applications involving repeated impacts of hard abrasive particles on surfaces at high or moderate strain rates. Operational conditions of components experiencing erosive and impact type wear are sometimes difficult to mimic in laboratory conditions, and as such, it is common to approach behaviour and lifetime predictions by meticulously studying different types of single impacts. This is particularly true for characterising and modelling of high strain rate impact events between hard particles and a wearing elastomer surface. This work presents and applies such a methodology for two specific elastomer materials: a natural rubber (NR) and styrene–butadiene rubber (SBR) compounds. The elastomer materials are subjected to quasistatic and dynamic testing conditions for determination of hyper- and viscoelastic material properties. The results are used in an iterative calibration procedure for establishing related constitutive models by applying the Ogden and Prony series models.

The Numerical Simulations for the Shot Peening Process

To develop a generalized numerical model by the elasto-plastic formulation coupling with dynamic finite element method for the shot peening process of metal alloys is the main goal of this paper. The analysis code is based on the finite deformation theory; the optimum numerical technique and the relevant parameters of forming process. In this study, the simulations of single and multi shot forming process were performed. The effects of impact velocity and strain rate, size of workpiece, and the residual stress were observed and discussed in details. After comparing with the corresponding papers, the universal model for metal shot peening analyses will be developed completely. The most significant advantage of this paper is the development of the precise analysis technology to suit for the future necessity of the manufacturing processes. The suggested models and techniques are helpful in solving of impact problems or metal forming processes.

Characterization of Impact Damage in Ultra-High Performance Concrete Using Spatially Correlated Nanoindentation/SEM/EDX

Little work has been done to study the fundamental material behaviors and failure mechanisms of cement-based materials including ordinary Portland cement concrete and ultra-high performance concretes (UHPCs) under high strain impact and penetration loads at lower length scales. These high strain rate loadings have many possible effects on UHPCs at the microscale and nanoscale, including alterations in the hydration state and bonding present in phases such as calcium silicate hydrate, in addition to fracture and debonding. In this work, the possible chemical and physical changes in UHPCs subjected to high strain rate impact and penetration loads were investigated using a novel technique wherein nanoindentation measurements were spatially correlated with images using scanning electron microscopy and chemical composition using energy dispersive x-ray microanalysis. Results indicate that impact degrades both the elastic modulus and indentation hardness of UHPCs, and in particular hydrated phases, with damage likely occurring due to microfracturing and debonding.

Numerical study of strain-rate effect in cold rolls forming of steel

Cold roll forming (CRF) is a well-known continuous manufacturing process, in which a flat strip is deformed by successive rotating pairs of tools, without changing the material thickness. In the past decades, to lessen the process-development efforts, finite-element simulations have been increasingly employed to improve the process design and predict the manufacturing-induced defects. One of the important aspects in design of the CRF process is consideration of resulting strains in the final product as the material passes through several complex forming stands. Sufficient knowledge of longitudinal strain in the workpiece is required to set various process parameters. Increasing a process speed in a roll forming operation can bring cost advantages, but the influence of the forming speed on the strain distribution should be explored.This study is focussed on a strain-rate effect in the CRF process of steel sheets. The strain-rate dependency of a plastic behaviour observed in most metals can affect the finished product's quality as well as process parameters. This paper investigates the influence of the strain rate on longitudinal strains induced in the roll forming operation by incorporating a phenomenological Johnson-Cook constitutive model, which allows studying the impact of the process speed on the output product. Taking advantage of 3D finite element analysis, a roll forming process was simulated using MCS.Marc, comprising a complete set of forming stations. Through the changing of the process speed, the strain rate impact on longitudinal peak strains and forming length was investigated. The results highlight the effect of the strain rate on edge thinning and subsequent undesirable distortions in the product.

Effect of Thermo-Mechanical Treatment on Mechanical Properties of AlCuMg Alloys

Technology development and new grades of alloys creation put before construction materials the number of requirements in range of durability and reliability of created constructions. Receivers expect materials with high strength properties, low production cost of the finished product, availability, corrosion resistance and low specific gravity. So the specific needs of customers mean that studies are constantly associated with the exploration of new materials and technologies that could meet made requirements [1,2,. In large scale this demand is met through the use of non-ferrous metals and their alloys. Selection of appropriate manufacturing techniques and the use of heat treatment procedures allow to obtain materials with better mechanical properties. Here the leading role has the aluminium and its alloys. Due to specific mechanical properties aluminium based materials are used in almost each field of industry. In aircraft industry they are used for the manufacture of fuselage elements in automobile industry the light alloys are used to make cylinder blocks, and other elements of internal combustion engines. In the construction industry they are used to manufacture windows and doors, as well as beautiful self-supporting lightweight facades. While the aluminium alloy products such as films or cans are also used in the food industry. The combination of physico-chemical and mechanical properties of aluminium alloys makes them the optimal solution for innovative design, thanks to them engineers can provide high strength associated with very low gravity. This allows to minimize the costs of subsequent use of the product, and while achieving good strength parameters. As part of this work the analysis of strain rate and temperature impact on mechanical properties of the tested alloy will be carried out. The experimental studies conducted in the temperature range of recrystallization (test temperature: 400°C, 450°C, 480°C, 500°C) using two strain rates 1 s-1and 0,1 s-1. This paper present the analysis of the application of high-temperature deformation changes in structure mainly caused by the dynamic recrystallization processes, which determine the optimal parameters of AlCuMg deformation process [. The proposed methodology of the research work made it possible to determine the effect of temperature-velocity parameters to changes in mechanical properties (inter alia: microhardness measurements) and changes in the structure of the material, which are closely related to the level achieved in mechanical properties.