Strain Rate Dependent Material Properties Research Articles

Wear Evolution on PVD Coated Cutting Tool Flank and Rake Explained Considering Stress, Strain and Strain-Rate Dependent Material Properties

Impact loads developed on a tool cutting edge when milling into a workpiece material are prevailing metrics for explaining coating fatigue failure and the subsequent tool-wear evolution. For predicting related stress and strain fields in the compound coating-substrate, stress, strain, and strain-rate, dependent material properties are required. The attainment of such data is briefly described in the paper. Considering these data, the occurring strains in the cutting edge at various entry impact durations, i.e., strain rates, were calculated and compared with fatigue-critical strains. In this way, the wear phenomena causing the coating failure on the flank and rake during milling were clarified. The attained results were also correlated to corresponding ones in turning, where the dynamic loads of the cutting edge are comparably negligible. The conducted investigations showed that the fatigue-critical strains strongly diminish, when the relevant strain rates increase; thus, leading to a remarkable tool-life reduction. This happens, because the increase of the strain-rate restricts the time for the dislocations movements; thus, regions with stress concentrations occur, deteriorating the material ductility, increasing its brittleness, and diminishing the fatigue critical strains. In cutting operations, where the coating fatigue is the main wear factor, the tool-life can be predicted considering these phenomena. In the paper, relevant experimental analytical procedures are introduced.

Stress, strain and strain-rate cemented carbide properties determined with a fem-supported evaluation of impact test imprints

Cemented carbide materials are key in tool manufacturing, nowadays widely used in cutting, forming and other manufacturing processes. Commonly applied methods for obtaining their strain-rate dependent material properties are insufficient due to the high hardness, mechanical strength and low deformability. In this paper, we produce relevant data for stress-strain and strain-rate curves up to strain rates of approximately 200 s−1 with the aid of a developed FEM-supported evaluation method for remaining imprints on cemented carbide surfaces after applying impact loads at various durations and magnitudes. Regarding the impact duration, the impact loads were dynamically generated via electromagnetic or piezoelectric devices. The attained data are relevant to several applications including calculations to determine the stress and strain fields developed in cemented carbide tools imposed by impact loads at various conditions.

Strain-rate dependent material properties of selective laser melted AlSi10Mg and AlSi3.5Mg2.5

Abstract This paper investigates the mechanical properties of two selective lasermelted aluminum alloys (AlSi10Mg and AlSi3.5Mg2.5) under high strain-rate uniaxial loading. Accelerated tensile tests were performed under various strain-rate decades (.ε = 4.7 × 10-3 up to 250 s-1) to determine the load-speed-specific changes in the mechanical properties. As a result of the primary laser-based shaping process, the microstructure and characteristics change was entirely comparable to the conventional manufacturing of aluminum parts. Based on an ultrafine microstructure, parts achieve high strength along with a brittle fracture behavior. Modifications for applications requiring high ductility (e. g., the crashloaded structural parts of a car body) can be made through specific heat treatment strategies. The experimental results demonstrate that a significant increase in ductility (factors 4-5) with a concurrent decrease in strength can be obtained compared to the as-built state. In high-speed tests, the tensile strength of both alloys rose strain-rate dependently around 10 %, and the elongation at break increased relatively by ≈ 15 % for AlSi10Mg and ≈ 10 % for AlSi3.5Mg2.5.

A MEMS dynamic mechanical analyzer for in situ viscoelastic characterization of 3D printed nanostructures

Cellular metamaterial structures with sub-micron features have shown the ability to become excellent energy absorbing materials for impact mitigation due to the enhanced mechanical properties of materials at the nanoscale. However, in order to optimize the design of these energy absorbing metamaterial structures we need to be able to measure the dynamic properties of the sub-micron features such as storage and loss moduli and the loss factor. Therefore, at scale testing is required to capture the scale, temperature, and strain rate dependent material properties of these nanoscale materials. This paper presents the design, fabrication, and calibration of a MEMS-based dynamic mechanical analyzer (DMA) that can be directly integrated with the two photon lithography (TPL) process commonly used to fabricate metamaterial structures with nanoscale features. The MEMS-based DMA consists of a chevron style thermal actuator used to generate a tensile load on the structure and two differential capacitive sensors on each side of the structure used to measure load and displacement. This design demonstrated 1.5 ± 0.75 nm displacement resolution and 104 ± 52 nN load resolution, respectively. Dynamic mechanical analysis was successfully conducted on a single nanowire feature printed between the load and displacement stages of the MEMS device with testing frequencies ranging between 0.01–10 Hz and testing temperatures ranging between 22 °C–47 °C. These initial tests on an exemplar TPL part demonstrate that the printed nanowire behaves as a viscoelastic material wherein the transition from glassy to viscous behavior has already set in at the room temperature.

Strain-rate dependent material properties of selective laser melted AlSi10Mg and AlSi3.5Mg2.5

Abstract This paper investigates the mechanical properties of two selective lasermelted aluminum alloys (AlSi10Mg and AlSi3.5Mg2.5) under high strain-rate uniaxial loading. Accelerated tensile tests were performed under various strain-rate decades (.ε = 4.7 × 10-3 up to 250 s-1) to determine the load-speed-specific changes in the mechanical properties. As a result of the primary laser-based shaping process, the microstructure and characteristics change was entirely comparable to the conventional manufacturing of aluminum parts. Based on an ultrafine microstructure, parts achieve high strength along with a brittle fracture behavior. Modifications for applications requiring high ductility (e. g., the crashloaded structural parts of a car body) can be made through specific heat treatment strategies. The experimental results demonstrate that a significant increase in ductility (factors 4-5) with a concurrent decrease in strength can be obtained compared to the as-built state. In high-speed tests, the tensile strength of both alloys rose strain-rate dependently around 10 %, and the elongation at break increased relatively by ≈ 15 % for AlSi10Mg and ≈ 10 % for AlSi3.5Mg2.5.

Study about the Effect of Addition of Carbon Nanofibers on the Strain-Rate Sensitivity of Thermoplastic Polymer Matrix Nanocomposites Manufactured by Ultrasonic Processing

Polymer nanocomposites based on polypropylene (PP) reinforced with carbon nanofibers (CNFs) at a fixed concentration of 0.5% w/w were prepared by precipitation from liquid solutions of PP and CNFs. Ultrasonic processing was used as the primary process for mixing both PP and CNFs in the the solvent, while mechanical stirring was also used as a control process to prepare similar samples. Thermogravimetric analysis (TGA) shows that the ultrasonic processing influences little on the thermal stability of the polymer material. Moreover, ultrasonically-processed PP shows higher tensile strength and better ductility, compared to those of the neat PP. Although the mechanically-processed PP has about 10% higher tensile strength than the ultrasonically-processed one, it is observed that there is a significant deterioration in its ductility due to the dissolution of calcium carbonate which is used as an additive for the neat PP. The advantage of significantly reduced material processing time, increased mixing efficiency, and increase in thermal stability and mechanical properties of ultrasonically-processed PPs indicated that the ultrasonic processing is relatively more effective and efficient mixing process compared to mechanical stirring for preparation of the polymer and its nanocomposite. Tensile tests were also conducted using quasi-static strain rates from 10-4 to 10-1 s-1 in order to obtain the tensile strength, elongation at fracture, and the elastic modulus of injection molded polymer and its nanocomposite. PP-CNF nanocomposites exhibited higher strain-rate sensitivity within the tested strain range, compared to the neat PP.Both the neat PP and PP-CNF nanocomposite exhibited strain-rate dependent material properties, showing an increase in tensile strength, and decrease in elongation with increasing strain rates.

Material properties of human lumbar intervertebral discs across strain rates

BACKGROUND CONTEXTThe use of finite element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire. PURPOSEThe aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates. STUDY DESIGNA human cadaveric experimental study coupled with an inverse finite element study. METHODSTo predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39±19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate. RESULTSExperimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the annulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young modulus of AF fibers (—MPa) to strain rate (ε˙, /s) relationship of YMAF=31.5ln(ε˙)+435.5, and the C10 parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa. CONCLUSIONSThese material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications. CLINICAL SIGNIFICANCEFinite element models can be used for many applications including investigating low back pain, spinal deformities, injury biomechanics, implant design, design of protective systems, and degenerative disc disease. The accurate material properties obtained in this study will improve the predictive ability, and therefore clinical significance of these models.

Strain rate dependent thermo-mechanical aspects of glass fiber reinforced thermoplastic based on experimental data

Thermo-mechanical material considerations have been published since two centuries. A new method of correlating experimental field information of strain and heat generate data for a physical based thermo-mechanical modeling of strain rate dependent material properties. Strain rate dependent characterizations under tensile loading of glass-fiber reinforced thermoplastic (LFRT) and its matrix material polypropylene (PP) were conducted. Higher fracture strains of LFRT with raising strain rate could be ascertained in contrast to the decreasing fracture strain of PP. High-speed video based digital image correlation (DIC) in combination with high-speed infra-red (IR) measurements provide field data of the deformation and the temperature evolution. A precise IR calibration method, the correlation of the Lagrangian deformation field with the Eulerian temperature field, the contemplation of volume specific values and the incorporation of the thermo-elasticity allowed the determination of the heat transition values βdiff(ϵ,ϵ˙) with respect to strain and strain rate. The results show clear difference of (βdiff) between PP and LFRT. While PP shows a higher βdiff with rising strain rate and therefore higher energy dissipation, βdiff of LFRT decreases with the strain rate. The predominant role of thermo-elasticity was identified as the key-factor of higher energy absorption of LFRT at higher strain rates.

A new constitutive model for steel fibre reinforced concrete subjected to dynamic loads

The use of steel fibre reinforced concrete (SFRC) in protective structures has gained worldwide interest due to its superior mechanical characteristics. At present, hydrocode material models have been frequently used to simulate the dynamic behaviour of SFRC subjected to impact and blast loads. However, as these material models are developed for normal concrete, much effort is required for model calibration, and their other drawbacks, such as the neglect of shear dilation and the inappropriate consideration of strain-rate effect, may lead to inaccuracies in numerical predictions. In this study, a new constitutive material model is developed for SFRC, in which the damage evolution, shear dilation and strain-rate dependent material properties are properly taken into account. The new material model could accurately capture the mechanical behaviours of SFRC (i.e. strain hardening and softening in both compression and tension) with simple input parameters. It is then incorporated into the commercial finite element code LS-DYNA to simulate the structural behaviour of SFRC components under various loading conditions. The effectiveness and accuracy of the new material model are validated against the reported experimental results.

Evaluation of a novel test method for the determination of strain rate-dependent material properties of high-performance fibers

For reinforcement in fiber reinforced plastic and concrete applications, the knowledge of the high-velocity impact and crash behavior of typically used high-performance fibers, such as carbon fibers (CF), becomes an important aspect for designing and dimensioning new composite components. More important than the impact velocity is the resulting strain rate in the fiber, which defines the failure behavior. In current literature, there is still an open gap for fiber material testing for strain rates between 100 and 1000 1/s, which is difficult to close with the existing measurement setups, i.e. between servo-hydraulic tensile testing machines and Split-Hopkinson-tension-bars. A rotary drive principle is proposed where the challenge arises in coupling the force, in a reliable clamping of the specimens and in high-speed acquisition of the stress-strain curve. In the implementation process, speeds up to 40 m/s were currently achieved, which corresponds to a strain rate of 267 s-1 for a specimen length of 150 mm. The specimen and the moving elements were prepared with stochastic patterns and evaluated by means of digital image correlation (DIC). The force signal is recorded and correlated from a piezoelectric load cell. Additional information on the energy dissipated by the tensile test was acquired by analyzing the engine control records. The evaluation of high-speed images by DIC shows that there is a partially elastic impact and acceleration reaches its maxima before the specimen’s rupture. Thus, for a precise evaluation, the stress equilibrium has to be taken into account and the impact process has to be further optimized.

Dynamic spherical indentation of strain hardening materials with and without strain rate dependent deformation behavior

Dynamic spherical indentation of elastic-plastic solids is examined in the light of finite element simulations. The deformation behavior of indented solids is described by two constitutive models – elastic-plastic strain hardening with or without strain rate dependent deformation. Numerical results of dimensionless global field parameters that describe the deformation response, such as mean contact pressure, contact area, and plastic work, are presented for a range of indentation velocity and elastic–plastic material properties. The dynamic contact response is interpreted in terms of a dimensionless indentation parameter, the normalized indentation strain, and the strain hardening and strain rate dependent material properties. It is shown that generalized solutions of global field parameters can be obtained in terms of the indentation parameter and indentation strain over a certain range of indentation depth. The results of this study provide new insight into the role of strain hardening and strain rate dependent deformation on the dynamic contact response of elastic-plastic solids.

The study of material flow behaviour in dissimilar material FSW of AA6061 and Cu-B370 alloys plates

Friction stir welding is a solid-state joining process which proved to be very effective for similar low strength materials. However, the joining of dissimilar materials is far complex than the similar materials because of divergent material properties. The need to study friction stir welding of dissimilar materials is inevitable due to increasing demand of modern industries. In the current study, the joining of aluminium alloy (AA-6061) and copper alloy (Cu-B370) plates is accomplished for studying the material flow movement throughout welding zone. A novel material flow model for dissimilar material friction stir welding is proposed based on the temperature and strain rate dependent material properties. The model used the volume of fluid (VOF) approach in the commercial FVM package ANSYS fluent 14.5. Experiments are also conducted to validate the model with thermal profiles and optical micrographs. Furthermore, the effect of tool rotational and the welding speed are studied on the material movement. It is found that process parameter had a huge impact on the nugget zone formation during the welding. The tool rotaion and welding speed directly affect the amount of platisized material mixing.

Numerical analysis of tunnel in rock with basalt fiber reinforced concrete lining subjected to internal blast load

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the threedimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors\' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings.

Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10−3 to 6000 s−1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper–Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper–Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.

Experimental and numerical investigation of Long Glass Fiber Reinforced Polypropylene composite and application in automobile components

Due to the good mechanical performances and design flexibility of Long Glass Fiber Reinforced Polypropyl-ene (LGFRP) composite, it has been increasingly used in the automotive components, in which the LGFRP components are likely to sustain different strain rates loading during a crash event. This study aims to investigate the correlations between the LGFRP and strain rate, which will be applied to crash-worthiness and energy absorbing property analysis of a bumper beam under the longitudinal impact. Firstly, strain rate dependent material properties are determined, for which the experimental procedure is explained in detail on the tensile specimens of long glass fiber and polypropylene matrix based composite configurations. The gained experimental results provide the input parameters for a numerical analysis of specimens. The numerical results of properties are compared with those from tests. The constitutive model that fits for LGFRP is employed to crash-worthiness and energy absorbing property analysis of a bumper beam under the longitudinal impact. First Published Online: 17 May 2017

Energy-based numerical modeling of the strain rate effect on fracture toughness of SA508 Gr. 1a

This article presents an energy-based method to simulate ductile tearing under dynamic loading conditions. The strain rate–dependent material properties are characterized by the Johnson–Cook-type model. The damage model is defined based on the multi-axial fracture strain energy concept. The proposed damage model is applied to simulate the fracture toughness test of SA508 Gr. 1a under four different test speeds. Simulated results show a good overall agreement with the experimental results.

Dynamic Analysis of Tunnel in Weathered Rock Subjected to Internal Blast Loading

The present study deals with three-dimensional nonlinear finite element (FE) analyses of a tunnel in rock with reinforced concrete (RC) lining subjected to internal blast loading. The analyses have been performed using the coupled Eulerian–Lagrangian analysis tool available in FE software Abaqus/Explicit. Rock and RC lining are modeled using three-dimensional Lagrangian elements. Beam elements have been used to model reinforcement in RC lining. Three different rock types with different weathering conditions have been used to understand the response of rock when subjected to blast load. The trinitrotoluene (TNT) explosive and surrounding air have been modeled using the Eulerian elements. The Drucker–Prager plasticity model with strain rate-dependent material properties has been used to simulate the stress–strain response of rock. The concrete damaged plasticity model and Johnson–Cook plasticity model have been used for the simulation of stress–strain response of concrete and steel, respectively. The explosive (TNT) has been modeled using Jones–Wilkins–Lee (JWL) equation of state. The analysis results have been studied for stresses, deformation and damage of RC lining and the surrounding rock. It is observed that damage in RC lining results in higher stress in rock. Rocks with low modulus and high weathering conditions show higher attenuation of shock wave. Higher amount of ground shock wave propagation is observed in case of less weathered rock. Ground heave is observed under blast loading for tunnel close to ground surface.

Investigation of bullet penetration in ballistic gelatin via finite element simulation and experiment

To qualitatively understand the deformation processes and damages in the human body caused by high-speed impact, we conducted experimental and computational investigations for bullet penetration into viscoelastic ballistic gelatin blocks. Because it is difficult to measure the strain rate-dependent material properties of viscoelastic gelatin blocks during high-speed impact, the material properties that are indirectly defined by the stress relaxation test were used for the computational simulation. We also conducted some firing experiments and analyzed the deformation processes of the structures. In particular, the passing through times and the shapes of the temporary and permanent cavities inside the ballistic gelatin blocks were analyzed and compared. This data reveals that the employed material models, with some modifications for the FE simulation, are sufficient for predicting the high-speed impact behaviors. To investigate the shapes of the permanent cavities and fragments made by bullets inside the gelatin blocks, two-dimensional sectional images were taken by an industrial CT scanner and a three-dimensional CAD model was constructed based on these images.

Voids and their effect on the strain rate dependent material properties and fatigue behaviour of non-crimp fabric composites materials

The manufacture of composite structures is inevitably linked to the formation of voids. Several non-destructive techniques are potentially able of detecting defects, but just the exact knowledge of the effects of defects on the mechanical properties allows the definition of thresholds for the purpose of quality management. In this paper an experimental program for characterizing the effect of voids on the composite materials behaviour is presented. Therefore glass fibre non-crimp fabric reinforced epoxy composites were produced using vacuum assistant resin transfer moulding. For obtaining various void contents specially modified process parameters were used. Nominally defect free specimens are compared with flawed specimens. Tensile testing at different loading speeds and fatigue tests in tension-compression loading are performed.

Comparative performance of composite sandwich panels and non-composite panels under blast loading

The performance of non-composite panels built of steel plates, concrete slabs, and composite sandwich panels in blast response reduction is examined and compared in the present study. The dynamic response of steel stiffened and unstiffened plates, plain concrete, reinforced concrete, and steel fiber reinforced concrete slabs, stiffened and unstiffened steel-foam-steel, and steel-sand-steel sandwich panels is investigated through three-dimensional finite element analyses. Parametric studies are performed considering different stiffener configurations, panel thicknesses, materials in the composite sandwich panels (e.g. polyurethane, dytherm, cenosphere aluminum alloy syntactic foams, and sand), and varying thicknesses of foam and sand layers. Strain rate dependent material properties for steel, concrete, steel fiber reinforced concrete, foams, and sand are used in the analyses. Blast load is modeled using an equivalent pressure time history curve calculated as per the TM5-1300 manual and the modified Friedlander’s equation. The central node displacement of the panels for peak blast overpressure 1.16 MPa applied for 6.1 ms is studied. The results indicate that the non-composite panels made up of steel fiber reinforced concrete slabs and cenosphere aluminum alloy syntactic foam composite sandwich panels show excellent blast response reduction capability as compared to (a) steel plate, (b) plain and reinforced concrete slabs, and (c) polyurethane and dytherm foam cored composite sandwich panels.