Strain Rate Properties Research Articles

A Novel Image-Based Inertial Impact Test (IBII) for the Transverse Properties of Composites at High Strain Rates

Current methods for testing the high strain rate properties of composites require multiple assumptions that limit achievable strain rates. Therefore, this study presents a new method for testing the transverse properties of composites at high strain rates using ultra-high speed imaging. The image-based inertial impact test developed here uses the reflection of a compressive stress wave to generate tensile stress in the specimen. Throughout the test, full-field displacement measurements are taken. The acceleration and strain fields are then derived from the displacement fields. The acceleration is then used to calculate the average stress in the specimen. This paper describes the optimisation of the experimental configuration using simulations and the experimental validation of the technique. The elastic modulus and tensile strength were identified at strain rates of ∼ 2000 s−1. The results showed an increase of 8% in elastic modulus and an increase of 57% in strength compared to quasi-static values.

Study on micro-structure and dynamic mechanical properties of machined surface layer by aluminum alloy 7050-T7451

Surface micro-structure of a machined workpiece has an important effect on functional performance. During machining, the change of grain size is closely related to dynamic mechanical properties. Turning experiment was conducted via changing turning speed and rake angle with aluminum alloy 7050-T745, and then ultra-depth microscope and transmission electron microscope (TEM) were used to observe and analyze the micro-structure and grain refinement of turning machined surface layer. Afterwards, under the same cutting condition, the DEFORM finite element simulation software was used to simulate the strain, strain rate, temperature and other dynamic mechanical properties in the plastic deformation zone. The results show that the dislocation multiplication is the main cause of grain refinement, and the change of dislocation density is directly related to the dynamic mechanical properties parameters. The turning speed is in negative linear correlation with strain, strain rate and the temperature, while the grain size on cutting surface layer is reduced along with the increase of turning speed.

An Image-Based Inertial Impact (IBII) Test for Tungsten Carbide Cermets

Testing tungsten carbide cermets at high strain rates is difficult due to their high stiffness and brittle failure mode. Therefore, the aim of this study is to apply the image-based inertial impact (IBII) test methodology to analyse the high strain rate properties of tungsten carbide cermets. The IBII test uses an edge on impact test configuration with a narrow stress pulse. The narrow input pulse travels through the specimen in compression and reflects in tension causing failure. Full-field measurements of acceleration and strain are then coupled with the virtual fields method to identify the stiffness components and tensile strength of a test sample at high strain rates. Image deformation simulations were used to select optimal test processing parameters and predict the associated experimental errors. The elastic modulus and tensile strength of the tested tungsten carbide cermet samples were successfully identified using the IBII test at strain rates on the order of 1000~text{s}^{-1}. No significant strain rate dependence was detected for either the stiffness or tensile strength.

High Strain Rate Dynamic Deformation of ADI

Engineering materials used in numerous applications, particularly in automotive crash loading and military ballistic purposes have to meet new demands, one of which is the resistance to dynamic loading. As the phenomena associated with such interaction is rather complex, non-static types of tests are applied to evaluate and compare between different potential materials. In this Work, different grades of ADI were produced under different austenitizing and austempering conditions different ausferrite morphologies. The effect of alloying elements such as Cu and Mo on the initial microstructure of the ductile iron was also studied. The initial amount of retained austenite was subjected to different dynamic strain rates. The hardness and strain induced martensitic transformation as a function of the microstructure and strain rate were evaluated. Extensive use of XRD and SEM was made to evaluate the high strain rate properties of the investigated grades.

High strain-rate behavior and deformation mechanism of a multi-layer composite textured AZ31B Mg alloy plate

There are currently very few studies on the high strain-rate properties of Mg alloys with multi-layer composite textures under dynamic loading. In present study, a multi-layer composite textured AZ31B Mg alloy plate was fabricated using the asymmetric twin-roll casting process. The high strain-rate (∼103 s−1) deformation behaviors of the AZ31B plate along the normal direction (ND) were investigated using split-Hopkinson pressure bar technique. The microstructural evolution and deformation mechanism were analyzed by optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy methods. The experimental results show that the mechanical behaviors exhibit a power-law hardening response under high strain-rate deformation. The flow stress generally increases with increasing strain rate, whereas the strain-hardening rate decreases with increasing strain. An interesting feature is that the maximum flow stress at high strain rates is much lower than that at its corresponding quasi-static counterpart. Microstructure analysis demonstrates that the characteristic layered texture and microstructure along the ND determine its mechanical behavior. The plastic deformation is mainly controlled by the basal-type texture, where the predominant deformation mechanism is dislocation slip. Dynamic recrystallization (DRX) occurred unevenly in the material during dynamic deformation, resulting in a moderate increase in ductility. The fracture behaviors change from brittle fracture to ductile fracture as the strain rate increases. The energy absorption capacity is therefore enhanced due to the occurrence of both DRX and the brittle–ductile transition at high strain rates.

Derailment-resistant performance of modular composite rail track slabs

Railway transportation, comprising freight and passenger transport, is the lifeblood of the social economy of a country today, especially for developing countries. Despite over a decade of operations, derailment accidents are among the most frequent accidents for railway transportation and may cause fatally or severe injury to passengers, loss of property and damage to the railway track. Hence, this study focuses predominantly on the structural response and performance evaluation of composite rail track slabs through 3D finite element analysis using ABAQUS. The response and performance of composite track slab subjected to derailment actions has been observed. Material strain-rate properties and impact loads have been introduced to the numerical simulation in order to investigate impact behaviours of composite slabs subjected to derailment loading in explicit dynamic analysis. Based on obtained results, it was found that 45 km/h in the direction of gravity is the limit impact velocity for the designed composite rail track slab. The outcome of this study will improve the design standard and calculation of composite rail track slabs subjected to derailment actions.

Combined shear/tension testing of fibre composites at high strain rates using an image-based inertial impact test

Testing fibre composites off-axis has been used extensively to explore shear/tension coupling effects. However, off-axis testing at strain rates above 500 s-1 is challenging with a split Hopkinson bar apparatus. This is primarily due to the effects of inertia, which violate the assumption of stress equilibrium necessary to infer stress and strain from point measurements taken on the bars. Therefore, there is a need to develop new high strain rate test methods that do not rely on the assumptions of split Hopkinson bar analysis. Recently, a new image-based inertial impact test has been used to successfully identify the transverse modulus and tensile strength of a unidirectional composite at strain rates on the order of 2000 -1. The image-based inertial impact test method uses a reflected compressive stress wave to generate tensile stress and failure in an impacted specimen. Thus, the purpose of this study is to modify the image-based inertial impact test method to investigate the high strain rate properties of fibre composites using an off-axis configuration. For an off-axis specimen, a combined shear/tension or shear/compression stress state will be obtained. Throughout the propagation of the stress wave, full-field displacement measurements are taken. Strain and acceleration fields are then derived from the displacement fields. The kinematic fields are then processed with the virtual fields method (VFM) to reconstruct stress averages and identify the in-plane stiffness components G12 and E22.

A micro-mechanical modeling approach for dynamic fragmentation in brittle multi-phase materials

Understanding the response of structures exposed to high rate mechanical loading is important for improved protection and security. Modeling the behavior of these structural materials and components can be performed at different scales. However, a detailed picture of the behavior of the material under high strain rates can only be gained by treating each of its components independently. In this work, we present a one-dimensional finite element model to study dynamic fragmentation in multi-phase materials, and we applied it to study masonry as an example of multi-phase material for structural applications. The model follows a micro-mechanical approach where the matrix (brick), inclusions (mortar), and interfaces between matrix and inclusions are represented separately. Within each constituent, the heterogeneity in the material is introduced through a critical strength distribution. A cohesive zone model has also been incorporated to model progressive damage. Results show the influence of the volume fraction and the inclusion size on the average fragment-size and fragment-size distributions for strain rates between 102 and 105 s−1. Based on these results, a mathematical expression that captures the dependence of the average fragment-size on the strain rate, volume fraction and inclusion size has also been formulated. The observed increase on the average fragment-size with decreasing the inclusion size suggests the existence of a critical length that depends on the strain rate and material properties below which, no additional fragments of the inclusion-material are created.

Modelling the strain rate sensitivity on the subsurface damages of scratched glass ceramics

Abstract Some applications of glass ceramics components require high surface finish and low subsurface damage. However, the machining process of glass ceramics can easily cause surface and subsurface damage. To reveal the dynamic effect of strain rate caused by machining speed on damage induced during machining, this paper proposes a new theoretical stress field model in which the strain rate effect is introduced for estimating plastic deformation and cracks. This model was established based on the relationship between the strain rate and material properties. This model provides an insight into the effect of strain rate and scratch speed on plastic deformation and cracks. To validate the present model, scratch experiments were conducted on glass ceramics using an ultra-precision machine. The findings show that the plastic deformation radius, and median crack length decrease as scratch speed increases, while the actual ductile-to-brittle transition depth increases with the increase of the scratch speed. Furthermore, the area of the plastic zone and median crack length as predicted by the developed model were compared with experimentally obtained values. The comparison results show that the predicted values are consistent with the experimental measurements. Thus, the proposed model can evaluate the plastic deformation and median crack length, which determine the dimension of the subsurface damage layer. This study is expected to provide guidance for machining-induced damage design and the manufacture and application of glass ceramic components.

Compressive behavior and constitutive model for roller compacted concrete under impact loading: Considering vertical stratification

This paper presents fundamental investigation on the dynamic compressive behavior and constitutive model of roller compacted concrete (RCC) at intermediate strain rates. Dynamic uniaxial compression tests of RCC specimens were performed by split Hopkinson pressure bar (SHPB). Then, the dynamic compressive properties of RCC material under intermediate strain rate are investigated in terms of failure pattern, stress-strain curve, dynamic increase factors (DIF) of compressive strength, Young’s modulus and critical strain at peak stress. The polynomial fitting method (in terms of lgε̇) was well adapted to describe the empirical strain rate effect. The vertical stratification of RCC caused by different mix proportion and compacted layer structure has influence on its dynamic mechanical behavior. Due to the statistically discreteness of RCC material, the distributions of dynamic mechanical properties were analyzed with statistics theory. A new statistical constitutive model was proposed with statistical analysis, in which the two main parameters were related to strain rate and conventional mechanical properties. Finally, the developed constitutive model is verified and demonstrated to be high applicability to RCC material and improves the estimations of the dynamic mechanical properties of RCC.

Overview of Composite Metal Foams and Their Properties and Performance

This paper reviews the background and evolution of composite metal foam (CMF) from its inception until now. A broad understanding of the processing and basic mechanical, microstructural, and physical properties of different types of composite metal foams is discussed in the first part of the paper. In the second part, some recent studies on high strain rate properties, ballistic performance, radiation attenuation, and thermal properties of composite metal foams are discussed and compared with other bulk and control materials. These properties suggest many potential applications for this novel material in a broad range of engineering structures from ballistic armors to trains', cars', buses', helicopters' crashworthiness systems, and many others such as nuclear casks and thermal insulating units.

High strain rate behavior of STF-treated UHMWPE composites

This study systematically investigates the effect of Shear Thickening Fluid (STF) treatment on the high strain rate properties of UHMWPE (Ultra High Molecular Weight Poly Ethylene) composites. Spherical nanosilica particles of size 100nm were used for the synthesis of STF. The high strain rate impact studies were accomplished on in-house designed and fabricated Split Hopkinson Pressure Bar (SHPB) experimental set-up. Compression moulded UHMWPE variant Gold Shield® was used as the ballistic composite. Both STF-treated as well as neat Gold Shield® specimens were subjected to high strain rate impact testing. From the experimental results and Fractography studies it was revealed that STF treatment enhanced the ballistic resistance of Gold Shield® composite material. In the SHPB experiments, the improved ballistic performance of STF-treated Gold Shield® specimens was manifested in terms of higher peak stress, specimen strain rates and impact toughness.

The influence of fluid - flexible particle interaction on fluid flow optical non-homogeneity in channel bifurcation

In the present paper the peculiar properties of convergent fluid flow in T-junction channel is considered. There is no interaction between flexible particles in the flow. Such kind of situation is described by rheological FENE-P and Oldroyd-B models. The first one predicts viscosity anomaly, dependence of longitudinal viscosity on longitudinal strain rate and elastic properties; the last one – existence of longitudinal viscosity depending on longitudinal strain rate and having a physical sense only for and elastic properties. The model’s governing parameters are the Weissenberg number (We), the Reynolds number (Re), the ability of flexible particle to change its orientation and stretching degree (L2) in the main flow. The bifurcation area is of great importance due to possibility of high stresses and velocities existence not only in central area, but also on the walls and near the corners. The symmetry-loss effect at creeping flows regime (Re≪1) is investigated. It has been showed that at certain set of We and L2 values the symmetrical shape of fluid flow turns to asymmetrical shape.

Effect of Specimen Thickness on High Strain Rate Properties of Kevlar/Polypropylene Composite

Characterization of Kevlar-Polypropylene based composite material system under high strain rate loading has been investigated using Split Hopkinson Pressure Bar (SHPB) test for varying specimen aspect ratios. Flat laminates of 16, 24 and 30 layered Kevlar composite were compression molded and laser machining to get cylindrical specimensof desired aspect ratios. Based on SHPB experiments, stress-strain plots were obtained and analysed to reveal compressive material behaviour as function of growing strain rate. The peak stress, strain and toughness exhibited considerable increase with growing strain rate of loading. With increasing strain rates peak specimen stress increased by 90%, for lowest thickness composite. The aspect ratio studies suggests application of thin laminates for better performance of composite laminates.

The influence of strain rate and pulp properties on the stress relaxation of wet paper — modeling of relaxation

The time-dependent stress (tension) relaxation behavior of wet paper plays a key role in web transfer from the press to the dryer section of a paper machine. In this study, three linear viscoelastic models were used to predict the short time range tension relaxation of wet paper. Over longer time periods, all three models gave relaxation moduli that were apparently linear on a logarithmic timeline. However, the results showed that the tension relaxation of wet paper had more than one characteristic time constant, meaning that the initial tension relaxation phase had a different constant than the later phase or phases. In practical applications, the most relevant time range for runnability of the wet paper web is from milliseconds to a few seconds. The obtained results suggest that the strain rate and initial tension of the relaxation dictate the shape of the tension relaxation curve of wet paper: the higher the strain rate, the greater the tension loss during the first second of relaxation. The tension relaxation behavior of wet paper did not generally depend on pulp type, refining level of pulp, or solids content. However, there can be significant differences between furnishes and solids content in the amount of draw that leads to a sufficient web tension. The results indicated that the tension relaxation behavior of wet paper may be based on a general viscoelastic mechanism that is independent of fiber network properties but depends on the fiber wall material. The findings suggest that the redistribution mechanism of stresses in the wet fiber network has a high level of regularity. The Prony series was capable of predicting tension relaxation behavior of wet paper over a wide time range. Therefore, it can be a very useful simulation tool not only for wet webs, but for any viscoelastic material that shows stress (tension) relaxation.

An experimental study of high strain-rate properties of clay under high consolidation stress

A split Hopkinson pressure bar (SHPB) combined with high pressure consolidation apparatus and high speed camera was used to obtain dynamic compressive stress-strain curves of clay whose over consolidation stress state in the process of formation was properly considered. The stress-strain relationship at various high strain rates from 60s−1 to 600s−1 was obtained. The strain rate and degree of consolidation effects on the compressive response of the consolidated clay were determined. The results show that the dynamic mechanical properties of clay in high pressure consolidation is sensitive to strain rate, and parameters like dynamic strength, failure strain and so on are significantly improved compared with unconsolidated clay which indicate that the initial stress history of the soil materials is also one of the most important factors that affect the dynamic mechanical response.

High Strain Rate and Shock Properties of Hydroxyl-Terminated Polybutadiene (HTPB) with Varying Amounts of Plasticizer

Hydroxyl-terminated polybutadiene (HTPB) has long been used as a binder in propellants and explosives. However, cured HTPB polyurethanes have not been characterized in a systematic fashion as a function of plasticizer content. In this study, three isocyanate-cured HTPB variants with different amounts of plasticizer were formulated. The materials were characterized across a range of strain rates from 10−3 to 106 s−1. Group interaction modeling (GIM) was used to predict the material behavior based on the underlying structure of the polymer. Increasing the amount of plasticizer was found to reduce the strength of the material across all strain rates. GIM was found to overpredict the modulus but predicted the shock response very well.

Assessment of right ventricular function in patients with first inferior myocardial infarction: strain imaging study

Objective: The aim of the study was to assess strain and strain rate (SR) properties of the right ventricle (RV) in patients with RV myocardial infarction (MI). Background: Quantitative assessment of RV function is still challenging due to its complex anatomy and thin wall structure, and therefore is not incorporated into daily clinical practice. Two-dimensional strain and SR analyses are novel Doppler-independent techniques to obtain these measurements of myocardial movement and deformation. These methods have been frequently used to assess left ventricular function; however, they have yet rarely been used to examine RV function, despite RV function is an important prognostic factor in patients with acute first inferior MI. Patients and methods: A total of 40 patients with acute inferior MI were included in this study; 20 patients had ECG signs of inferior MI without RV infarction (group II) and 20 patients had ECG signs of inferior MI with RV infarction (group III). In all, 20 age-matched and sex-matched healthy volunteers were included as a control group (group I), using two-dimensional speckle tracking measurements of RV free wall longitudinal strain and SR in the apical four-chamber. Results: A statistically highly significant difference was found among the three groups regarding the peak systolic longitudinal strain at apical, mid, and basal segments of RV free wall (P Conclusion: This study demonstrates that RV strain and SR were lower in patients with left ventricular inferior wall MI with RV infarction compared with those without RV infarction.

The influence of strain rate and pulp properties on the stress-strain curve and relaxation rate of wet paper

Sufficient tension of the wet web is crucial for paper machine runnability. As profitability pressures have been increasing, the potential to improve runnability is of interest. The runnability of wet paper is especially important for paper machines running at high speeds, making paper at lower grammage, and using large amounts of filler or recovered paper. The typical location of web breaks depends on the paper grade and paper machine. A break typically takes place when the paper is wet and a fast draw is applied to the web. Because information on wet paper is scarce, especially information on the effect of strain rate on the tensile properties, we investigated the effects of strain rate on the tension-strain curve and relaxation of wet paper and how they depend on pulp type, refining, solids content, and fines. Higher strain rate leads to higher tensile strength, tensile stiffness, and relaxation rate. The initial wet strength and stiffness of the studied pulps, bleached softwood kraft pulp and bleached hardwood kraft pulp, were increased by increasing the solids content, fines, wet pressing, and refining. At a constant strain rate and constant strain, the tension at a certain moment depended strongly on the initial tension and thus on the tensile stiffness.

Prediction of fragmentation and experimentally inaccessible material properties of steel using finite element analysis

High strain-rate properties of materials are needed for predicting material behavior in extreme environments. The demand for high strain-rate properties continues to increase for commercial and military applications as the operating environments become more extreme, such as fragmentation, impact and explosions. To reduce time and expense, Finite Element Analysis (FEA) is being used to simulate these behaviors and reduce the number of experiments needed to characterize how a material performs at high-strain-rates. A finite element model for predicting fragmentation behavior of a high strength steel ring was developed using Abaqus Computer Aided Engineering (Abaqus) software. AISI 4340 steel, a low alloy Cr–Ni–Mo steel, was used in the analysis. The results of the finite element model were compared to the results from CTH, a two-dimensional Eulerian shock physics hydro-code. CTH was also used to develop a transient loading curve for the Abaqus model. The fracture strain in the model was adjusted to induce failure in the ring. Element deletion was used to model failure. A fracture strain less than 1×10−5 was needed to initiate fragmentation. The effects of mesh type and model defects were also investigated.