High Strain Rate Compression Loading Research Articles

Impact behaviour of Al 2014 wrought alloy using Split-Hopkinson pressure bar (SHPB): Its influence on mechanical and microstructural properties

The deformation behaviour of Al 2014 alloy under high strain rate dynamic load experienced in the actual service condition of aero-structural components is scarce in the literature. Therefore, Split Hopkinson Pressure Bar (SHPB) based high strain rate compressive behaviour (dynamic loading) of Al 2014 is investigated in this work. The wrought (WAR) form of Al 2014 alloy has been chosen to examine its deformation behaviour with varying high strain rate compressive loading, generated through 4 different pressure ranges (1 bar, 1.5 bar, 1.75 bar, and 2 bar) at striker bar end in SHPB technique. These pressure ranges induced high strain rates 5536/s, 6236/s, 6576/s, and 7783/s in separate WAR specimen, correspondingly, which were recorded as flow stress curves. Also, the WAR Al 2014 alloy was heat treated with standard Tempered-6 (T6) condition to homogenize its microstructure. The T6 condition was exposed further with the same pressure values, which induced high strain rates 5303/s, 6139/s, 6977/s, and 7861/s in T6 specimens. The SHPB-based flow stress responses for both WAR and T6 conditions were compared to understand high strain rate deformation behaviours. The WAR specimen exposed at 7783/s strain rate has shown superior Peak Stress (P.S., ∼765 MPa) and %contractionP.S. (∼15%) compared to its T6 counterpart (at 7861/s). Prior to the dynamic studies, the quasi-static responses were also explored through tensile, compressive and hardness measurements (with WAR and T6) to realize the overall materials' behaviour. These dynamic responses under high strain rate compressive loading were correlated with in-process microstructural evolution, explored through SEM and XRD techniques. Exhaustive EBSD analysis quantified the excellent peak stress and % contraction in WAR conditions due to presence of huge amount of low angle grain boundaries (∼85%), ultrafine grains, relatively textured microstructure ({111} 〈100〉, {101} 〈001〉, etc), and significant strain hardening phenomena, whereas large amount of high angle grain boundary (∼88%), equiaxed and uniform microstructure contributed for higher hardness (∼22%) and tensile strength (∼2%) in T6 conditions.

Dynamic mechanical response and fracture behaviour of Ti–Ni–C composites fabricated by directed energy deposition

This work studied the mechanical response and the associated microstructures and failure mechanisms of additively manufactured Ti matrix composites with in-situ synthesised Ti2Ni and TiCx reinforcements under a variety of loading rates. The composites were fabricated using directed energy deposition technique with Ti–6Al–4V (Ti64) and Ni coated graphite (NCG) powders. Different proportions of Ti64 and NCG were mixed to manufacture the specimens with different compositions. Compression tests were conducted at strain rates in the range of 10−3 to 800 s−1. Our results show that the metallurgical and mechanical properties of the composites change with the NCG fraction. The failure mechanisms of the composites are a combination of tensile fracture of brittle TiCx precipitates and shear of the Ti matrix. The composites with higher NCG content exhibit increased strength, reduced ductility and less strain rate sensitivity. Under high strain rate compression loading, the Ti–Ni–C composite can provide enhanced strength with the ductility unchanged, which make it a prospective material for the applications subjected to impact loads.

Exploring the Effect of Dispersed Phase on the High Strain Rate Mechanical Response of Nanosilica Dispersions

Shear Thickening Fluids (STFs) constitute a special class of materials which exhibit phase transition from low to high viscosity state when exposed to shearing forces, particularly, when the applied shear rate exceeds a critical value. The last decade has witnessed a mutual symbiotic relationship between STF and high-performance fabrics such as Kevlar®, Dyneema®, Ultra High Molecular Weight Polyethylene (UHMWPE) etc., to produce new light weight and flexible protective materials systems with enhanced knife, stab and ballistic resistant properties than the existing ones. In this study, we explore the effect of particle shape and size on the high strain rate dynamic response of nanosilica dispersions. Shear thickening fluid (STF) was synthesized using fumed silica and spherical nanosilica particles, comprising the dispersed phase, whereas PPG400 (Polypropylene Glycol) was used as the dispersion medium. Ultrasonic homogenization technique was used for the synthesis of STF. The low strain rate rheological characterization was conducted on MCR302 rheometer at 25°C, whereas the high strain rate characterization was performed on inhouse designed and developed SHPB (Split Hopkinson Pressure Bar) apparatus. Fumed silica (FS) particles possess high specific surface area owing to their fractal structure. Therefore, their low molecular weight dispersions exhibit shear thickening behavior thus making them potential candidates for liquid body armour applications. On the other hand, spherical silica dispersions exhibit shear thickening behavior in high phase volume concentrations. Experimental studies showed that spherical silica based STF dispersions exhibited enhanced shear thickening in the low strain rate domain, as well as better mechanical response in terms of higher peak stress under high strain rate compressive loading conditions, during SHPB testing, in comparison to their fumed silica counterpart. Thus, it can be inferred that the mechanical response of nano-silica dispersions is influenced by the shape of the particles constituting the dispersed phase.

Additively Manufactured Stochastic Sheet-Based Cellular Metamaterial: Quasi-Static and High Strain Rate Compressive Loading

Additively Manufactured Stochastic Sheet-Based Cellular Metamaterial: Quasi-Static and High Strain Rate Compressive Loading

Texture evolution during high strain-rate compressive loading of maraging steels produced by laser powder bed fusion

Dynamic mechanical behavior and texture evolution in maraging steels, manufactured using the laser powder bed fusion (LPBF) technique, was investigated at strain rates of 2000 s −1 , 2300 s −1 , 3200 s −1 for the as-built samples, and 650 s −1 , 680 s −1 , 950 s −1 for the heat-treated samples. Split-Hopkinson Pressure Bar (SHPB) was used for high strain rate compression tests. The texture of the deformed samples was measured using the electron backscattering diffraction (EBSD) technique. A strong strain rate dependence on the crystallographic texture of as-built LPBF-maraging steel samples was observed. However, strain rate does not have any significant effect on texture evolution in the heat treated maraging steel samples. • Maraging steels rod samples were produced using laser powder bed fusion technique (LBBF) and subjected to heat treatment at 490 °C for 6 h. • High strain rate compressive behavior of LPBF-maraging steel samples in as-built and heat treat conditions were investigated by Split Hopkinson pressure bar apparatus. • Texture of deformed as-built and heat-treated samples were studied by electron backscattering diffraction technique (EBSD) where significant texture development in as-built samples was observed and no texture change for heat-treated samples was seen.

High strain-rate dynamic compressive behavior and energy absorption of distiller’s dried grains and soluble composites with paulownia and pine wood using a split Hopkinson pressure bar technique

Novel bio-based composite wood panels (CWPs) that consisted of distiller’s dried grains and solubles (DDGS) flour adhesive bound to a wood filler/reinforcement were subjected to high strain-rate compression loading, and their behavior was investigated. Specimens of DDGS-Paulownia wood (PW) or DDGS-pinewood (Pine) composites made using DDGS with fractions of 10%, 15%, 25%, and 50% were tested at high strain-rates using a modified compression Split Hopkinson Pressure Bar (SHPB). Both DDGS-PW and DDGS-Pine composites displayed strain-rate sensitivity, and DDGS-PW had a 25% fraction, which showed the highest ultimate compressive strength of 655 MPa at approximately 1600/s. The 90%-PW had the highest specific energy of 19.24 kJ/kg at approximately 1600/s when loaded via dynamic compression. The CWPs constructed of DDGS-PW had higher strength and energy absorption than DDGS-Pine with the exception of the 50% DDGS composites.

Experimental study on compressive properties of SFRC under high strain rate with different fiber content and aspect ratio

The dynamic mechanical properties of steel fiber reinforced concrete (SFRC) depend largely on the content and size of steel fibers. This paper presents an experimental study on mechanical properties of SFRC under high strain-rate compressive loading. In order to explore the co-effect of the fiber content and aspect ratio on the dynamic performance of SFRC, the SFRC specimens with three kinds of fiber aspect ratio (30, 50, 60, respectively) and six kinds of fiber content (0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5% in volume fraction) were tested by Split Hopkinson Pressure Bar (SHPB) device with a diameter of 75 mm. The test strain rate ranged from 30 s−1 to 370 s−1. Test results show that SFRC has obvious strain rate effect. With the same fiber aspect ratio, the optimum fiber content of SFRC shows strain rate sensitivity. And with the increase of fiber content, the dynamic increase factor (DIF) of SFRC decrease gradually. With the same fiber content, SFRC with a fiber aspect ratio of 50 shows the maximum compressive strength at different strain rates. In addition, the study also proposed the expression of DIF, strain rate and fiber content of SFRC to each fiber aspect ratio.

HIGH STRAIN-RATE COMPRESSIVE TESTING OF FILLING MATERIALS FOR INTER-PENETRATING PHASE COMPOSITES

In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and (iii) polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected materials were tested in compression loading mode at strain-rates 1000 s−1 to 4000 s−1. The high strain-rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance. Based on the comparative measurement response to compression at both low and high strain-rates was analysed. The results show a significant strain-rate sensitivity of the ordnance gelatin and of the polyurethane putty, while strain-rate effect in the polyurethane foam was not observed.

Mechanical Behaviour of Nanostructured Bainitic Steel Under High Strain Rate Shear and Compression Loading

Mechanical Behaviour of Nanostructured Bainitic Steel Under High Strain Rate Shear and Compression Loading

Meso-scale modelling and failure analysis of kenaf fiber reinforced composites under high strain rate compression loading

This paper presents a multi-scale structure finite element modelling scheme to analyse the damage behaviors of Kenaf fiber reinforced composite materials subjected to high strain rate compressions. The proposed modelling framework includes a micro-scale structure model with periodic boundary conditions for homogenizing the heterogeneous fiber/resin system into a unit cell, and a meso-scale model with established constitutive relationship for the constituents integrated with failure criterion to account for the stiffness degradation and subsequent element removal. The finite element results from the model provide the localities of stress propagation, the stress distribution, and the progressive failure behaviour within the Kenaf fiber reinforced composite materials. The results which are stress-strain behaviour and developed damages are found to be in fair agreement with the available test data.

High strain rate response of bio-composites using split Hopkinson pressure bar and digital image correlation technique

ABSTRACTIn this research, high strain rate response and energy absorption characteristics under dynamic compression loading of five different bio-composites were studied using a compression split Hopkinson pressure bar (SHPB) and DIC (digital image correlation) technique. This study is to map suitability of plant-based materials instead of petroleum-based plastic as a constituent raw material in composites. Bio-composites panels were made from Southern yellow pine (SYP), Corn starch (CS), and Methylene diphenyl diisocyanate (MDI) using a Dieffenbacher hot press. The ability of non-contact DIC analysis served as a valuable tool to measure the strains over a large range of deformation in wood-based bio-composites subjected to high strain rate compressive loading. Among all, Material 2 bio-composite with high manufacturing pressure had highest peak strength, shows that material behaviour at high strain rates is strongly dependent on the manufacturing pressure during fabrication. Presence of corn starch marginally increased the energy absorption capacity.

Crushing Behavior of Graded Auxetic Structures Built from Inverted Tetrapods under Impact

In this study, the crushing behavior of auxetic structures built from inverted tetrapods with linearly graded porosity under impact is analyzed both experimentally and computationally. The auxetic samples with linearly graded porosity are fabricated from Ti‐6Al‐4V alloy powder by the selective electron‐beam melting method. A detailed geometrical analysis of the fabricated samples based on micro computed tomography (microCT) scans is performed to determine the variation of strut thickness and other fabrication imperfections. The samples are subjected to high strain rate compression loading in two specimen orientations (specimens with low or high porosity facing the impacting plate) using the powder gun. Appropriate computational models are later developed and validated to provide a more detailed insight into the crushing mechanism of auxetic structures during impact. The experimental and computational results show dependency of the plateau stress inclination (progressive/regressive) on the gradation of the auxetic cellular structures (specimens with low or high porosity in front). These initial results prove that it is possible to tailor the mechanical behavior of a porous structure with introduction of graded porosity, especially in the case of high strain rate impact, where the main deformation occurs at the impacting front.

Mechanical behaviour of auxetic cellular structures built from inverted tetrapods at high strain rates

Auxetic cellular structures build from inverted tetrapods were experimentally tested at high strain rate compression loading for the first time. The strain rates up to 10,000 s−1 were achieved with gas powder gun, where the shock deformation mode is predominant. The deformation localizes in the deformation front between the impacting specimen and the fixed plate due to the inertia effects. This deformation mode results in stiffness increases in comparison to the quasi-static response. The results from experimental testing were used for validation of developed computational models in finite element explicit code LS-DYNA. Furthermore, the validated computational models were used for critical strain rate analysis, determination of critical loading velocities and analysis of deformation modes together with analytical constitutive crushing models of cellular structures.

Dynamic characterization of biocomposites under high strain rate compression loading with split Hopkinson pressure bar and digital image correlation technique

ABSTRACTIn this paper, dynamic response and energy absorption characteristics of three different types of wood-based biocomposites have been investigated using a split Hopkinson pressure bar (SHPB). Different types of biocomposite panel were produced using a Dieffenbacher hot press with a particular composition of refined cotton motes, pure cotton, and sweet potato flour. The strain induced in the specimen under dynamic stress equilibrium was obtained using the SHPB. Impact event at the zone of specimen was captured using a Shimadzu HPV-2 high-speed video camera. Digital image correlation (DIC) was performed using Proanalyst to obtain the strain in the specimen. Excellent agreement was found between the strains obtained using the SHPB and DIC analysis over three strain rates on three types of biocomposites. The biocomposite produced with cotton motes had the highest ultimate strength and specific energy absorption among three different types of biocomposites tested in this study.

A study of strain-rate effect and fiber reinforcement effect on dynamic behavior of steel fiber-reinforced concrete

This paper presents an experimental study on uniaxial mechanical properties of steel fiber-reinforced concrete (SFRC) subjected to high strain-rate compressive loading. SFRC specimens of 6 different steel fiber volume fractions (0.0%, 0.75%, 1.5%, 3.0%, 4.5% and 6.0%) are fabricated and tested using a 75-mm-diameter split Hopkinson pressure bar (SHPB). Wave-shapers are investigated to ensure that two basic assumptions of SHPB hold true and that constant strain-rate is maintained within SFRC specimens. Based on acquired dynamic stress–strain relations, dynamic strength increase factor, fiber reinforcement factor, critical strain, and energy absorption are studied versus both strain-rate and fiber volume fraction. That provides an insight into strain-rate effect and fiber reinforcement effect on dynamic behavior of plain concrete and SFRC. The mechanisms underlying strain-rate effect and fiber reinforcement effect are discussed.

Characterization of 3D angle-interlock thermoplastic composites under high strain rate compression loadings

In the present work, dynamic compression response of polypropylene (PP) based composites reinforced with Kevlar/Basalt fabrics was investigated. Two homogeneous fabrics with Kevlar (K3D) and Basalt (B3D) yarns and one hybrid (H3D) fabric with a combination of Kevlar/Basalt yarns were produced. The architecture of the fabrics was three-dimensional angle-interlock (3D-A). Three different composite laminates were manufactured using vacuum-assisted compression molding technique. The high strain rate compression loading was applied using a Split-Hopkinson Pressure Bar (SHPB) set-up at a strain rate regime of 3633–5235/s. The results indicated that the dynamic compression properties of thermoplastic 3D-A composites are strain rate sensitive. In all the composites, the peak stress, toughness and modulus were increased with strain rate. However, the strain at peak stress of Basalt reinforced composites (B3D, H3D) decreased approximately by 25%, while for K3D specimens it increased approximately by 15%. The K3D composites had a higher strain rate as compared to the B3D and H3D composites. In the case of K3D composite, except strain at peak stress, remaining dynamic properties were lower than the B3D composite, however, hybridization increased these properties. The failure mechanisms of 3D-A composites were characterized through macroscopic and scanning electron microscopy (SEM).

Fracto-mechanoluminescent light emission of EuD4TEA-PDMS composites subjected to high strain-rate compressive loading

The objective of this study is to understand light emission characteristics of fracto-mechanoluminescent (FML) europium tetrakis(dibenzoylmethide)-triethylammonium (EuD4TEA) crystals under high strain-rate compressive loading. As a sensing material that can play a pivotal role for the self-powered impact sensor technology, it is important to understand transformative light emission characteristics of the FML EuD4TEA crystals under high strain-rate compressive loading. First, EuD4TEA crystals were synthesized and embedded into polydimethylsiloxane (PDMS) elastomer to fabricate EuD4TEA-PDMS composite test specimens. Second, the prepared EuD4TEA-PDMS composites were tested using the modified Kolsky bar setup equipped with a high-speed camera. Third, FML light emission was captured to yield 12 bit grayscale video footage, which was processed to quantify the FML light emission. Finally, quantitative parameters were generated by taking into account pixel values and population of pixels of the 12 bit grayscale images to represent FML light intensity. The FML light intensity was correlated with high strain-rate compressive strain and strain rate to understand the FML light emission characteristics under high strain-rate compressive loading that can result from impact occurrences.

A micromechanical model to study failure of polymer-glass syntactic foams at high strain rates

Syntactic foams are lightweight composite materials that find extensive application as core materials for sandwich panels in marine and aerospace structures. While several models have been proposed to analyze the elastic response and failure of these composites at small strain rates, the understanding of syntactic foam behavior at high strain rates remains elusive. In this work, we simulate the response of polymer-glass syntactic foams under high strain rate compressive loading conditions, by using a three-dimensional micromechanical model consisting of fifty hollow spheres randomly dispersed in the matrix material. The mechanical response of the matrix is described by generalizing a phenomenological viscoplastic constitutive model from the literature to the three-dimensional stress state. The filler behavior is assumed to be linear elastic until brittle failure, which is predicted on the basis of a structural criterion for glass microballoons. The collapse of the first glass microballoon is hypothesized to trigger the failure of the whole composite. Such a micromechanical model is implemented in the commercial finite element code ABAQUS. We focus on glass-vinyl ester syntactic foams and perform a parametric study to elucidate the roles of strain rate, microoballoon density, and microballoon volume fraction on the compressive modulus, strain energy, and effective strength. Comparisons between model findings and available experimental data are presented to assess the accuracy of the proposed numerical model. Our results enable the study of syntactic foam behavior at high strain rates, for a wide range of strain rates, microballoon densities, and microballoon volume fractions. This knowledge is expected to aid in the design of lightweight composite materials subjected to high strain rate compressive loading.

Deformation Response of Titanium Alloy under Static and Dynamic Loading

Response of a material under dynamic loading is different as compared to static loading. Dynamic material properties are therefore necessary for assessment of structural integrity and safety. Gas turbine aero engine frontal components like fan and compressors are critical and prone for foreign object impact as these components are exposed directly to the environment. Design of aircraft engine components like fan and compressor are critical and it is mandatory to design such components to withstand high impact loads. In view of this high strain rate test of Ti-6Al-4V alloy has been carried out in strain rate range of 1000 s-1 to 4000 s-1 using Split Hopkinson Bar (SHB). Force equilibrium analysis for each test is carried out to confirm the validity of the test results. Quasi-static test was also carried out for comparison with high strain rate test. From the tests, flow behavior of Ti-6Al-4V alloy at high strain rate is obtained. It is observed that the material have positive strain rate sensitivity and it fails by fracture under high strain rate compressive loading.

High strain-rate failure in carbon/Kevlar hybrid woven composites via a novel SHPB-AE coupled test

Abstract The high strain-rate induced failure characteristics in a carbon/Kevlar hybrid composite subjected to high strain-rate compressive loading were studied using a novel SHPB-AE coupled test. The tests were performed based on a split-Hopkinson pressure bar (SHPB) apparatus and an acoustic emission (AE) technique, respectively. Within the strain-rate range of 1002–1941 s −1 , a high strain-rate compressive test was conducted on the cylindrical carbon/Kevlar hybrid composite specimens located between the incident and transmitted bars. A wide bandwidth type AE sensor was connected to the specimen with a fine copper waveguide to monitor the AE signals in real time during the test. Specific types of failure mechanisms were observed with optical microscopy and scanning electron microscopy. First, AE characteristics originating from the specimens were investigated profoundly to distinguish the AE signals from diverse damage or failure sources. AE signals were then analyzed in terms of the AE amplitude, the AE count, the slope of cumulative AE count and the peak frequency. Finally, signals were classified into four types based on the waveform and corresponding peak frequency by a short time Fourier transforms (STFT). As a result, under high strain-rate compressive loading, the strain level at the damage initiation was shortened with increasing strain-rate. The failure process of the carbon/Kevlar hybrid woven composite showed initial matrix fracture and then brittle carbon fiber breakage. Subsequently, multiple failure mechanisms appeared, such as fiber-matrix debonding, fiber pull-out, excessive deformation and breakage in the Kevlar fiber tips including splitting and fibrillation. The application of the novel SHPB-AE coupled test to the carbon/Kevlar hybrid composite was discussed in depth for characterizing the failure process, and it was an effective and relevant methodology to grasp in situ information on the failures under high strain-rate compressive loading.