High Strain Rate Loading Research Articles

Optimization of multi-layered composites against ballistic impact: A mesoscale approach

There has been an urgent need to develop and analyse multi-layered composite structures with varying material properties to withstand projectile impact. The proposed study focuses on the optimization of the multi-layer composite to achieve maximum resistance/energy dissipation. This study investigates the mechanical performance of the proposed multi-layered composite configuration under high strain rate loading through a computational approach. The proposed multi-layered structure incorporates layers of reinforced concrete, boulders, an elastomer layer, an ultra-high-performance concrete panel, and a layer of steel plate. A mesoscale-based approach has been developed for the layer comprising boulders and mortar. A total of six different configurations have been considered to arrive at the most efficient one against projectile impact. Optimization of the proposed configurations has been done by utilizing the concepts of specific energy absorption and shock impedance. Additionally, the fracture and damage characteristics of each configuration are also studied. Ductile hole enlargement in the sandy soil layer, fragmentation failure in the boulders, petaling failure in the steel plate, and spalling failure in the concrete layer have been observed. Based on the specific energy absorption and shock impedance approaches, the optimum laying sequence for the ballistic impact of each material is suggested.

Design Optimization of Lattice Structures Under Impact Loading for Additive Manufacturing

Abstract Additive manufacturing (AM) has enabled the production of intricate lattice structures with excellent performance and minimal mass. Design approaches that consider static loading, including lattice-based topology optimization (TO), have been well-researched recently. However, to date, there appears to be no widely accepted method of optimizing lattice structures for high-strain rate loading, especially when the design for additive manufacturing (DFAM) principles are considered. This study proposes a computational framework for the design of lattice structures under specified impact loading. To manage dimensionality while achieving sufficient generality, a heuristic design space is developed that relies on traditional TO to govern the design's macrostructure and standard dimensioning to govern its mesostructure. DFAM principles are then incorporated into a Bayesian optimization scheme wrapped around traditional TO to achieve manufacturable designs that absorb high-impact loading. Because this approach does not require analytical gradient information, the framework can be used to optimize directly on complex objectives, such as injury metrics calculated from the acceleration curve. A series of case studies is formulated around a mass-performance tradeoff and involves individual unit cell design as well as full-part design. The proposed design parameterization is found to enable sufficient flexibility to achieve consistently good performance regardless of AM build orientation.

Residual mechanical properties of high strength concrete BBR9 subjected to dynamic uniaxial compressive loading

In recent years, enormous efforts have been devoted to accurately quantifying the residual load-bearing capacity of concrete at the material level when exposed to elevated temperatures. However, relatively less attention has been given to investigating the effects of dynamic events such as terrorist attacks, earthquakes, and hurricanes, which can cause complete collapse of concrete structures and have significant public and economic consequences. Hence, in the present study, a modified Kolsky compression bar system integrated with a momentum trapping technique was implemented to develop precisely controlled pre-/post peak high strain-rate loading to introduce distinctive states of damage inside the high strength concrete HSC-BBR9 specimens and to measure the corresponding plastic strain. Thereafter, the partially damaged specimens were tested to quantify the residual mechanical properties (e.g., residual stiffness and residual strength) at different plastic strain levels. Furthermore, a high-resolution laboratory micro-CT scanner was used to visualize the 3D crack network morphology in the partially damaged specimens. The findings demonstrated a remarkable decrease in the residual capacity with increasing levels of damage-induced plastic deformation. Additionally, the results showed a fundamental difference in the influence of internal damage on residual stiffness and strength to be acknowledged in the formulations of future constitutive damage models for concrete materials.

Dynamic Constitutive Model and Numerical Simulation of S32760 Duplex Stainless Steel Based on Dislocation Theory

Background: To describe the complex mechanical behavior of S32760 duplex stain-less steel under high strain rate and high-temperature loading conditions. Objective: The constitutive model of S32760 duplex stainless steel suitable for high strain rate was constructed from the micro-scale. Methods: Based on the theory of dislocation dynamics, the effects of different strain rates and strains on the plastic deformation of ferrite and austenite were analyzed, and the thermal stress term and non-thermal stress term of ferrite and austenite phases were coupled. Results: The simulation results of the model show that the S32760 dual-phase constitutive model has a high degree of fit with the experimental data at high strain rates. Conclusion: Compared with the classical J-C model, the results show that the constitutive model of this patent has more accurate predictability than the J-C model in describing the mechanical behavior of duplex stainless steel in the high strain range of 5000s-1 to 10000s-1.

Regulating loading strain rates under shockless quasi-isentropic compression using a resin-based areal density gradient flyer

Areal density gradient flyers (ADGFs) have important applications in quasi-isentropic compression and high strain rate loading. The wave impedance gradient distribution of the reported ADGFs is single, and the effects of different wave impedance gradient distributions and spikes number density on the loading results are unknown. In this study, the resin-based ADGFs with different spike areal density distribution and spikes number density were designed and prepared using projection micro stereolithography technology (PμSL). The printing accuracy of ADGFs was evaluated using three-dimensional optical profiler, optical microscope, Scanning Electron Microscopy (SEM) and ultra depth of field microscope. The loading process of the ADGF on the target was studied by experiment and simulation. The simulation result was consistent with the experimental result. Augmenting the wave impedance distribution index (P) of spikes and spikes number density increases the loading strain rate. Due to the high printing accuracy of PμSL, the fine ADGF structures with large spikes number density can be prepared, thereby promoting the formation of quasi-isentropic compression plane waves. This work realizes the regulation of loading strain rate under shockless quasi-isentropic compression, which is significant for understanding the mechanical response of materials under high strain rate loads.

Sustainability and Resiliency Investigation of Grouted Coupler Embedded in RC ABC Bridge Pier at Vehicle Impact

Increased occurrences of natural and man-made dynamic loading caused by high strain rate dynamic impact load have been recently reported. Different statistical results indicate that vehicular impacts occur more frequently compared to the other dynamic loads. However, existing literature primarily focuses on enhancing survivability and determining damage levels specifically in relation to faster bridge construction methods used as an accelerated bridge construction (ABC). In this context, the present study investigates the dynamic behavior of a commonly used connection type in ABC, namely grouted coupler that connects pre-cast elements like bridge piers and foundations. To execute the research, both the static and dynamic performance of grouted couplers embedded in pier foundation subjected to high strain rate loading incurred by high velocity vehicular impact are examined. A representative non-traditional reinforced concrete (RC) bridge pier is selected for the study with the standardized geometry and selected material properties. The use of splice sleeves as coupler materials and specified cross-sectional hollow cast iron cylinders filled with high strength concrete grout is employed for developing Finite Element (FE) modeling, extracting data from published journals. A commercial software, ANSYS, has been utilized to develop FE models to capture post impact respective static and dynamic behaviors, and the simulation results are then compared with the analytical. This also includes determining material performance via FE simulations. By considering dynamic loading, the dynamic impact factor (DIF) has been evaluated for the reinforcing steel bar adjacent and embedded into the coupler. In addition, dynamic simulations, and material modulus in demand to sustain impact are determined. Thus, the research necessitates mesh-independent sensitivity studies to investigate DIF corresponding to the precise outcomes. The findings of this study manifests valuable information that aids to opt for the suitable coupler connections, considering material properties, and adequate post impact execution. Consequently, it will serve as a useful design tool for design offices, structural practitioners, and forensic structural engineers.

The Influence of Strain Rate Behavior on Laminated Glass Interlayer Types for Cured and Uncured Polymers.

Recent explosions and impact events have highlighted the exposure of civil structures, prompting the need for resilient new constructions and retrofitting of existing ones. Laminated glass panels, particularly in glazed facades, are increasingly used to enhance blast resistance. However, the understanding of glass fragments and their interaction with the interlayer is still incomplete. This paper investigates experimentally the quasi-static and dynamic responses of cured and uncured polymers for seven different materials-two different products of polyvinyl butyral (PVB), two ethylene vinyl acetate products (EVA), one product of thermoplastic polyurethane (TPU), and two SentryGlas products (SG)-that were tested between 21 and 32 °C (69.8 and 89.6 °F), which is the recommended room temperature. In these experiments, the responses of PVB, EVA, TPU, and SG were evaluated under a quasi-static strain rate of 0.033 s-1 and compared to the results under a relatively higher strain rate of 2 s-1. Moreover, the high strain rate loading of the materials was accomplished using a drop-weight testing appliance to evaluate the engineering stress-strain response under strain rates between 20 and 50 s-1. The results demonstrated that with strain rates of 20 s-1, PVB behaved like a material with viscoelastic characteristics, but at 45 s-1 strain rates, PVB became a non-elastic material. SG, on the other hand, offered both a high stiffness and a high level of transparency, making it a very good alternative to PVB in structural applications. In contrast, after the maximum stress point, the response to the failure of the seven materials differed significantly. The tests provided ample information for evaluating alternative approaches to modeling these different materials in blast events.

Comparison of the Mechanical Properties and Approach to Numerical Modeling of Fiber-reinforced Composite, High-Strength Steel and Aluminum

The performance of carbon fiber reinforced polymer (CFRP) composite materials under quasi-static and high strain rate loading can be predicted with a high level of accuracy using the non-linear finite element analysis (FEA) method. Experimental validation tests under uniaxial tensile loading have shown a good correlation with FEA predictions for thermoset polymer composites, using commercially available epoxy resin MTM710 with carbon fiber reinforcement and for comparative tests on DP600 steel and aluminum alloys (AC170 and 5754 series). The physical and numerical results comparison of composite, aluminum, and high-strength steel indicates that the composite may be used as an alternative to aluminum and high-strength steel since the composite was shown to have almost the same strength as steel and higher strength than aluminum with the advantage of being lightweight and possessing similar mechanical behavior under quasi-static conditions. The results demonstrated that the strain rate range used did not significantly affect the strength of the composite materials. The selection of materials can be optimized reliably by FEA based on mechanical properties, cost, and weight. This will significantly reduce the new product introduction timescale, which is essential for the wider use of polymer composites for structural applications, especially in the automotive industry.

Study on the dynamic mechanical properties of winding‐block axial structure considering short circuit strain rate effect

AbstractTransformers may suffer multiple short‐circuit impacts during long‐term operation, and axial instability is one of the typical types of serious accidents caused by short‐circuit faults. The axial instability form of the winding‐block structure is analysed, and the dynamic solution of the winding short‐circuit electromagnetic force is obtained by establishing the three‐dimensional magnetic‐circuit‐force multi‐physical field coupling simulation model. The influence of strain rate on the cushion block constitutive equation is corrected, and the modified model is verified by short‐circuit impact test and quasi‐static test. The research results show that for 110 kV 31.5 MVA transformers, the maximum electromagnetic axial resultant force of winding is 363.16 kN, and the ultimate tilt force is 1214.2 kN. The pre‐tightening force configuration is accordingly recommended to range from 363.16 to 608.28 kN, which is narrowed by 18.49% compared with the static calculation method; Meanwhile, adding a logarithmic strain rate correction term to the classical constitutive equation of the cushion block can achieve a good correction of the stress‐strain relationship with the coefficient of determination above 0.99, and the cushion block has a larger elastic modulus under high strain rate load. The research results provide an important theoretical reference for the axial stability structure of transformers.

Quantitative study on dynamic instantaneous dissolution of precipitated phases in 2195-T6 Al-Li alloy based on characterizations with SANS and TEM

The kinetics of the dynamic instantaneous dissolution of the precipitated phases in 2195-T6 Al-Li alloy under high strain rate loading was firstly studied quantitatively by means of the small angle neutron scattering (SANS) and transmission electron microscopy (TEM) techniques, and the thermodynamics and transformation mechanism were also illustrated in this paper. The high strain rate loadings were performed by the split Hopkinson pressure bar. The maximum flow stresses increased but the pulse durations decreased with increasing strain rates. TEM observations indicated that the size and volume fraction of the T1 phases decreased. The SANS fitting results showed that the radius and volume fraction of the T1 phase decreased after loading. The dissolution activation energy (Qd) was calculated to be 28.4 kJ/mol by combining the Johnsone-Mehl-Avrami-Kolmogorov (JMAK) equation and the Arrhenius equation, indicating that the instantaneous dissolution of T1 phase was kinetically feasible. The T1 phase generated a larger distortion energy, and the surface energy as well as the internal pressure of T1 phase increased in dissolving during dynamic loading to increase the free energy difference (driving force for dissolving) between T1 phase and matrix, making the instantaneous dissolution of the T1 phases be thermodynamically feasible. The diffusion rates of Cu and Li atoms were significantly accelerated to promote the instantaneous dissolution of T1 phase particles. The results of the Vickers hardness values showed that the hardness increased after loadings, due to the high density of dislocations and only partial dissolution of the T1 phase particles.

Widely Employed Constitutive Material Models in Abaqus FEA Software Suite for Simulations of Structures and Their Materials: A Brief Review

The structural response of masonry/concrete structures depends upon the load-carrying mechanism and subsequently deformations produced by loads carried. In masonry/concrete structures, identification of the stress/strain imposing stress conditions and strain hardening/softening makes the structural response more complicated. Elastic damage models or elastic-plastic constitutive laws are inadequate to simulate masonry/concrete response under high strain-rate loadings. Further, irreversible or plastic strain cannot be realized using the elastic damage model. Several constitutive damage models are available in the literature. In this article, a concise explanation of the functioning of different material models in the Abaqus software package has been provided. These models include concrete damage plasticity for concrete and masonry, traction separation constitutive laws for brick-mortar interface, Hashin's criteria for CFRP, Johnson-Cook plasticity for steel, and crushable foam plasticity hardening for metallic foams. Researchers frequently utilize these models for numerical simulations and modeling of infrastructural elements and their respective materials when subjected to various structural loads. Besides, this paper presents a discourse on problem-solving methods and a comparison between explicit and implicit analysis. The research provides valuable input to researchers and practitioners in the field of structural engineering for an in-depth understanding of the functioning of Abaqus' pre-existing material models.

Compression behaviour of TiZrNbHf refractory high-entropy alloy upon high strain rate and high temperatures loading

Compression behaviour of TiZrNbHf refractory high-entropy alloy upon high strain rate and high temperatures loading

Compression behaviour of TiZrNbHf refractory high-entropy alloy upon high strain rate and high temperatures loading

Compression behaviour of TiZrNbHf refractory high-entropy alloy upon high strain rate and high temperatures loading

Dynamic Response Analysis of Reinforced Column Subjected To Shock Wave Loading

This study focuses on the dynamical response of reinforced concrete members subjected to shock-wave loading, which can cause catastrophic damage to structures. The effects of high strain rate loading and lateral confinement on the member’s behavior are considered in the analysis. The Moment-Curvature (M-ϕ) relations are assessed using stress block equilibrium at yield and ultimate state, and an analytical model is developed that integrates the high strain rate material behavior to predict the peak deflection of the structural member. The study evaluates the dynamic response of the member using a simplified model based on single degree of freedom (SDOF) idealization, and the response of the member in elastic and elastic-plastic phases is modelled using the bilinear resistance function. The governing equation of motion is explained using the Newmark-Beta algorithm, and the shock spectrum predicting the maximum deflection is developed by varying the load duration and magnitude. Additionally, a Finite Element (FE) model is developed to provide a more detailed understanding of the member’s behavior under shock loading. The results obtained from the FE model are compared with the analytical deflection for extreme combinations of load duration and magnitude. The study provides valuable insights into the behavior of reinforced concrete members under extreme loads, which can help structural designers in predicting and design structures that can withstand such loading conditions. The results can also be used in the development of building codes and standards to improve the safety and resilience of structures subjected to shock-wave loading.

Spall strength of additively repaired 304L stainless steel

Additive manufacturing has the potential to repair damaged parts, but the performance of additive materials under high strain rate loading is still uncertain—especially with the added complexity of an interface with an existing wrought material. In this work, 304L stainless steel samples were intentionally damaged and then repaired with wire-fed laser additive manufacturing. The samples were subjected to shock loading to generate incipient spall. Velocimetry and post-mortem metallography results show that when the additive repair process parameters are optimized to reduce porosity and match the equation of state of the original material, the influence of the repair region on the shock propagation is negligible. The free-surface velocity profile and internal damage morphology of the repaired sample are shown to be practically identical to the pristine material.

Ignition and energy release characteristics of energetic high-entropy alloy HfZrTiTa0.2Al0.8 under dynamic loading

Steel-like density HfZrTiTa0.2Al0.8 high entropy alloy (HEA) with a density of 7.78 g/cm3 is designed and fabricated as a novel energetic structural material (ESM). The microstructure, thermal analysis, compressive mechanical properties, ignition and energy release under dynamic loading are systemically investigated. The experimental results show that the HfZrTiTa0.2Al0.8 HEA has a single BCC solid solution structure, and spinodal decomposition with elements segregation in the nanoscale is observed. Thermal analysis shows the HEA keeps stable in the Ar atmosphere and the oxidizing reaction occurs in the Air atmosphere. The mechanical properties show brittle characteristics with maximum strength with 1520 MPa and fracture strain 0.07 and strain rate effect from 0.001s−1 to 3000s−1 is observed. Under high strain rate loading, the fracture-induced spark is observed, which is caused by an oxidizing reaction due to the rise. By direct ballistic test, the energy release velocity threshold is measured as 980 m/s, and the energy release intensity is more violent in higher velocity impact conditions. Moreover, the impact reaction degree is increased with increasing fragmentation degree and adiabatic temperature rise induced by impact. The designed HEA-ESM is a promising candidate that simultaneously possesses both high strength, high reactive heat and excellent energetic characteristics in the application field of high-strength ESM fragment.

Superior Strain Rate Strengthening Effect and Ductility of a Ti-4.5Al-2.9V-3Fe Alloy under High Strain Rate Loading

Superior Strain Rate Strengthening Effect and Ductility of a Ti-4.5Al-2.9V-3Fe Alloy under High Strain Rate Loading

Revealing the dynamic behavior and micromechanisms of enhancing the formability of AA1060 sheets under high strain rate deformation

Developing high strain rate (HSR) forming technologies is significant for efficient and high-quality aerospace sheet metal parts manufacturing. Research on the deformation behaviors and micromechanism of materials under HSRs will contribute to the further application of HSR forming technologies. In this study, the mechanical behavior of AA1060 pure aluminum at low strain rates (LSRs, 0.001 s−1 and 0.1 s−1) and high strain rates (HSRs, 2400 s−1 and 3300 s−1) was tested utilizing quasistatic tensile tests and Hopkinson bar tests at room temperature. The results of the mechanical properties showed that the elongations were 30.01 %, 37.91 %, and 46.61 %, corresponding to strain rates of 0.1 s−1, 2400 s−1, and 3300 s−1, respectively, which were 29.86 % at a strain rate of 0.001 s−1. The maximum amplification of AA1060 elongation reached 56.10 % at the HSR. Microstructure characteristics, including the Schmid factor distribution, geometrically necessary dislocation (GND) distribution, slip band, and dislocation cell, were observed by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM) under the condition of the same elongation with strain rates of 0.001 s−1 and 3300 s−1. In addition, the reasons for the plastic improvements during HSR loading were also investigated. The hard-oriented grains participate in plastic deformation at HSRs, providing additional space for dislocation multiplication and movement, increased dislocation density, and interaction between dislocations. In addition, the deformed hard-oriented grains also coordinated the strain gradient with soft-oriented grains. This improved the overall deformation uniformity, thus avoiding the premature occurrence of strain localization, namely, the elongation increase.

Mechanical properties of graphene-mortar at high strain rates

Graphene has been considerably studied as a reinforcing nanomaterial in cementitious composites to improve their mechanical properties under quasi-static loading. However, there is still lack of knowledge in graphene cementitious composites under high strain rate loadings. This paper reports the reinforcing effect of graphene on the mechanical behaviour of mortar at high strain rates. Different graphene contents were incorporated into the mortar to study their effect on the behaviour of mortar quasi-statically and dynamically. Compressive and split tensile strengths were measured under low and high strain rates using a universal testing machine and split-Hopkinson pressure bar (SHPB), respectively. It was found that adding 0.05% and 0.01% of graphene to the mortar enhanced the dynamic compressive and split tensile strengths up to 30% and 9.5% at 175 s-1 and 2–5 s-1 strain rates, respectively. Moreover, to understand the macroscale mechanical behaviour of the graphene mortar, Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS) and Mercury Intrusion Porosimeter (MIP) were employed to explore the morphology, porosity and hydration products of graphene mortar. The results indicated that graphene acted to fill the voids as well as to impede the crack path.

Research on damage failure mechanism and dynamic mechanical behavior of layered shale with different angles under confining pressure

AbstractThe hydrostatic or confining pressure of deep rocks has a significant impact on the mechanical behavior of brittle materials. Especially when confining pressure is applied, the mechanical properties of rock materials will undergo significant changes. Considering that the process of shale sample subjected to impact load is in a closed container in the dynamic triaxial SHPB test, the failure process of the sample cannot be observed. Meanwhile, the activation volume of the shale sample would be large and local failure would occur in the test under the high strain rate loading. Therefore, the finite element model of shale considering the bedding effect under confining pressure was established in this study. Taking shale materials with different bedding dip angles as simulation objects, the dynamic failure characteristics of shale were studied using the dynamic analysis software ANSYS/LS‐DYNA from three aspects: stress‐strain curve, failure growth process, and failure morphology. The research results obtained can serve as the key technical parameters for deep resource extraction.