High Strain Rate Properties Research Articles

High temperature and high strain rate properties of brazed honeycomb liner material Haynes 214

Abradable honeycomb sealing systems are essential for gas turbine efficiency. Experimental data on the rubbing performance of Haynes 214 metal sheets brazed with the nickel-chromium-silicon filler metal BNi-5 is presented. The brazing layer in the double foiled honeycomb sections turned out to have a major impact on rubbing behavior. Damage on the rotor was analyzed with a large chamber scanning electron microscope and energy-dispersive X-ray spectroscopy. The results demonstrate a significant influence of the brazing process on the mechanical properties, especially after exposure to 1000 °C. A hard aluminum nitride phase formed in the brazed metal sheets can cause severe damage to the rotor.

Effect of MWCNT on CFRP impregnated with shear thickening fluids under high strain rate impact

This study investigates the effect of multi-walled carbon nanotubes (MWCNT) on the high strain rate properties of carbon fiber reinforced polymer (CFRP) fabric impregnated with shear thickening fluids (STF). Three GFRP-STF and twelve GFRP-MWCNT/STF composite specimens were conducted using a split Hopkinson pressure bar (SHPB). Spherical silica nanoparticles (20.0 wt%) and polyethylene glycol were used to prepare silicon-based-STF (SiO2/STF). On this basis, MWCNT with 0.4, 0.8, and 1.2 wt% were further used to synthesize the MWCNT/STF, respectively. The SHPB test showed that MWCNT/STF has a more significant strain rate effect, with stress increases of 71.1%, 57.5%, and 26.0% under 3800 s−1, 5100 s−1, and 6100 s−1, respectively. The results also showed that MWCNT significantly improved the yield stress and strain energy absorption of SiO2/STF under a high strain rate. The maximum yield stress increase was 71.1%, and the maximum increase in strain energy absorption was 229.1%. The results of CFRP-MWCNT/STF revealed that MWCNT/STF treatment enhanced the high strain rate impact properties of CFRP-SiO2/STF. The improved effect is up to 27.9%, 133.6%, and 165.7% in yield stress, impact toughness, and energy absorption efficiency, respectively. The mass fraction of MWCNT significantly affects the impact properties of CFRP-MWCNT/STF under high strain rate loading, but this effect decreases with the increase of strain rate. Thus, CFRP-MWCNT/STF is more suitable for application in a high strain rate impact environment than CFRP-SiO2/STF.

Numerical Simulation of High Strain Rate and Temperature Properties of Laser Powder Bed Fusion Ti6Al4V(ELI) Determined Using a Split Hopkinson Pressure Bar.

Numerical models can be useful for analysis of the ability of structural engineering materials to withstand harsh environmental conditions such as dynamic loading. In the present study, a microstructure-variable-based numerical model for predicting the high strain rate and temperature properties of different microstructures of Ti6Al4V (ELI-Extra Low Interstitial) produced by laser-based powder bed fusion is proposed. The model was implemented in two different subroutines, VUMAT and VUHARD, available in ABAQUS/Explicit for simulating dynamic conditions. The two subroutines were then used to simulate the split Hopkinson pressure bar (SHPB) experiments to study the flow properties of various forms of the direct metal laser sintered Ti6Al4V(ELI) alloy at various conditions of strain rate and temperature. Comparison of the results obtained through simulation and those obtained from experimental testing showed high degrees of correlation and accuracy with correlation coefficients and absolute percentage errors >0.97 and <4%, respectively. The numerical model was also shown to give good predictions of the strain hardening and dynamic recovery phenomena that prevail for deformations at high strain rates and temperatures.

High Strain Rate Properties of Various Forms of Ti6Al4V(ELI) Produced by Direct Metal Laser Sintering

For analysis of engineering structural materials to withstand harsh environmental conditions, accurate knowledge of properties such as flow stress and failure over conditions of high strain rate and temperature plays an essential role. Such properties of additively manufactured Ti6Al4V(ELI) are not adequately studied. This paper documents an investigation of the high strain rate and temperature properties of different forms of heat-treated Ti6Al4V(ELI) samples produced by the direct metal laser sintering (DMLS). The microstructure and texture of the heat-treated samples were analysed using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction detector for electron backscatter diffraction (EBSD) analysis. The split Hopkinson pressure bar (SHPB) equipment was used to carry out tests at strain rates of 750, 1500 and 2450 s−1, and temperatures of 25, 200 and 500 °C. The heat-treated samples of DMLS Ti6Al4V(ELI) alloys tested here were found to be sensitive to strain rate and temperature. At most strain rates and temperatures, the samples with finer microstructure exhibited higher dynamic strength and lower strain, while the dynamic strength and strain were lower and higher, respectively, for samples with coarse microstructure. The cut surfaces of the samples tested were characterised by a network of well-formed adiabatic shear bands (ASBs) with cracks propagating along them. The thickness of these ASBs varied with the strain rate, temperature, and various alloy forms.

Cold spray particle impact simulation using the Preston-Tonks-Wallace plasticity model

In the Cold Spray process, solid powder particles are heated and accelerated to approximately 800 m/s by injecting them into a pressurized gas stream that is expanded through a converging-diverging nozzle. The high velocity particles impact a substrate and undergo severe plastic deformation at very high strain rates. The impact generates a bond between the particles and the substrate, or on particles already deposited on the substrate. The process parameters for each material system are developed experimentally. The most common method of predicting particle deformation was to use a constitutive equation such as the Johnson-Cook material model that is a curve fit of measured high strain rate properties. However, the constant for these types of models have to be determined experimentally for each material of interest and this model does not incorporate important impact events such as rebound of the particle. To better predict particle deformation and to reduce the need for experimental data, a thermodynamics based material model developed by Preston et al. was implemented through a user developed subroutine in finite element analysis. The model was used to predict the deformation of single particles at different impact velocities. The model showed excellent agreement with experimental single particle impact data provided by other universities. No adjustment to the material parameters was required. The development of the model will be explained and model results for deformation will be presented.

High strain rate impact effect and failure behavior of 3D six-directional braided composites

The high strain rate impact effect and failure behavior of three-dimensional six-directional (3D6d) braided composites with different braiding angles are reported in this paper. The results show that 3D6d braided composites exhibit typical strain rate sensitivity. Under out-of-plane dynamic compression, the stress–strain curves rise linearly and present obvious softening characteristics. With the increase of strain rate, both the strength and modulus of composites increase, while the failure strain decreases. Moreover, the composites with larger braiding angle exhibit higher dynamic curves and better out-of-plane high strain rate properties. The fracture morphology shows that composites exhibit different dynamic damage and failure modes at different strain rates and braiding angles. As the strain rate increases, the composites show clearer shear fracture feature and more severe brittle failure. The damage is mainly manifested as shear of the sixth and braiding fibers, tear of the fifth fibers on the shear plane, interfacial debonding and matrix cracking. As the braiding angle increases, the damage and fracture of composites are reduced obviously and the composites become less brittle failure at high stain rates.

High Strain Rate Mechanical Properties of SAC-Q With Sustained Elevated Temperature Storage at 100 °C

Abstract Leadfree electronics in harsh environments often may be exposed to elevated temperature for the duration of storage, transport, and usage in addition to high strain rate triggering loads during drop-impact, vibration, and shock. These electronic components may get exposed to high strain rates of 1 to 100 s−1 and operating temperatures up to 200 °C in critical surroundings. Doped SAC solder alloys such as SAC-Q are being considered for use in fine-pitch electronic components. SAC-Q consists of Sn-Ag-Cu alloy in addition to Bi (SAC+Bi). Prior data presented to date for lead-free solders, such as SAC-Q alloy, at high aging temperature and high strain rate are for 50 °C sustained exposure. In this paper, the effect of sustained exposure to temperature of 100 °C on high strain rate properties of SAC-Q is studied. Thermally aged SAC-Q samples at 100 °C have been tested at a range of strain rates including 10, 35, 50, and 75 s−1 and operating temperatures ranging from 25 °C up to 200 °C. Stress–strain curves are established for the given range of strain rates and operating temperatures. Also, the computed experimental results and data have been fitted to the Anand viscoplasticity model for SAC-Q for comparison.

Effect of Stress-Relieving Heat Treatment on the High Strain Rate Dynamic Compressive Properties of Additively Manufactured Ti6Al4V (ELI)

A study was undertaken on the compressive high strain rate properties and deformation behaviour of Direct Metal Laser-Sintered (DMLS) Ti6Al4V (ELI) parts in two separate forms: as-built (AB) and stress relieved (SR). The high strain rate compression tests were carried out using a Split Hopkinson Pressure Bar test system at ambient temperature. The average plastic strain rates attained by the system were 400 s−1 and 700 s−1. Comparative analyses of the performance (flow stresses and fracture strains) of AB and SR specimens were carried out based on the results obtained at these two plastic strain rates. Microstructural analyses were performed to study the failure mechanisms of the deformed specimens and fracture surfaces. Vickers microhardness test values were obtained before and after high strain rate compression testing. The results obtained in both cases showed the strain rate sensitivity of the stress-relieved samples to be higher in comparison to those of as-built ones, at the same value of true strain.

Effects of process parameters on the microstructure and mechanical properties of medium-carbon steels for improving high-strain rate properties

The effects of accelerated continuous cooling and isothermal heat treatment process on the microstructure and mechanical properties of medium carbon bainitic steels was investigated to find an alternative process of the conventional austempering treatment process. Two kinds of medium carbon steel billets melted by Vacuum Induction Melting (VIM) were hot rolled to the thickness of 6∼12mm plates and accelerated-cooled to predetermined temperatures and then isothermal heat treatment was conducted immediately. For quantitative analysis of microstructures, the fraction of constituent phases such as retained austenite, martensite, and bainite was measured by XRD and dilatometry. A series of hardness, tensile, and impact tests was conducted to evaluate the mechanical properties of the plates. As the finish cooling temperature increased, the fraction of retained austenite increased and the fraction of martensite and bainite decreased due to the differences in carbon diffusion and transformation kinetics during isothermal heat treatment process. Microstructural observation results showed that the lath/block thickness and fraction of bainite and martensite were mainly dependent on austempering temperature and time. The thickness of bainite and the fraction of martensite were found to be the major factors influencing mechanical properties of the present medium-carbon nanostructured bainitic steels.

Investigation on microstructure and high strain rate behaviour of pure tantalum prepared by hot press and subsequent annealing treatment

ABSTRACTAmong refractory metals, tantalum has long been the primary material of use in high strain rate applications. Hot pressing (HP) is a technique to produce specimens with high density and homogeneous microstructure. The individual effect of the HP or annealing heat treatment on high strain rate properties of tantalum powder compacts has been investigated, but little attention has been paid to the combined effect of subsequent annealing. In this study, the effect of annealing on the microstructure and mechanical properties of tantalum subjected to hardness and Split Pressure Hopkinson Bar (SHPB) test was investigated. After annealing at 1100°C, the grains are coarsened, thereby hardness and upper yield strength decreased to value 199 VHN and 1833 MPa, respectively. Moreover, an obvious increase in plasticity and toughness is detected at this temperature, indicating subsequent annealing is beneficial to improve the deformation properties of HPed powder compacts; the maximum plasticity of tantalum was 31.74% after annealing.

Effect of cyclic heat treatment on the microstructure and mechanical properties of W-Ni-Co alloys

Current generation heavy alloys with enhanced static as well as high strain rate properties are based on W-Ni-Co alloys. These alloys are subjected to a cyclic heat treatment to obtain fine tungsten precipitates in the matrix and to realise superior mechanical properties. The present study is focused on processing 92W-5Ni-3Co alloy using a post-sintering cyclic heat treatment to obtain fine tungsten precipitates in the matrix. As-sintered alloys and cyclic heat treated (in vacuum) alloys are then subjected to (i) vacuum heat treatment with oil quenching and (ii) nitrogen heat treatment with water quenching. A comparison has been drawn based on microstructural features and mechanical properties, between the alloys processed (i) with and without cyclic heat treatment and (ii) with oil and water quenching. This study thus helps in understanding the effect of cyclic heat treatment and quenching medium on the microstructure and mechanical properties of W-Ni-Co alloys.

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.

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.

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.

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.

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.

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.