Effect Of Strain Rate Research Articles

High-temperature dynamic failure behavior and compressive mechanical properties of alumina porous ceramic with various pore sizes

The dynamic compressive mechanical properties of alumina porous ceramic with various average pore sizes are tested at strain rates and temperatures ranging from 0.01 s−1 to 2900 s−1 and 20 °C to 850 °C, respectively. The corresponding 3d Voronoi models are employed to simulate the meso‑characteristics of cells and failure characteristics of alumina porous ceramic in multiscale. The failure in macroscale of quasi-static compression is fragmentation, and that of dynamic compression is comminution. But in mesoscale, the failure, both of quasi-static and dynamic compression, is the fracture of cell walls. Its dynamic strength increases with the increase of strain rate, but decreases with the increase of temperature and average pore size. The increase in temperature and average pore size leads to a decrease in its strain rate sensitivity. Its Young's modulus is not sensitive to the strain rate, but increases with the decrease of average pore size, and decrease with the increase of temperature, which is presented as a temperature and average pore size dependent function. The strain rate and temperature effects are also presented by average pore size dependent functions, respectively. A constitutive model is proposed based on them. It shows that the constitutive model fits well with the experimental results.

Experimental study on fractal dimension of energy dissipation and crack growth in saturated tuff at different strain rates

In order to investigate the effects of strain rate and water saturation on the energy dissipation and crack growth of tuff, uniaxial compression tests were carried out on dry and water saturated tuff with different strain rates using an electro-hydraulic servo press and a 50 mm diameter split Hopkinson pressure rod (SHPB) device. High-speed camera and Image J image analysis software were used to obtain the crack growth process of the specimen under impact load, and fractal dimension was introduced to quantitatively study the crack growth degree. The results show that more than 90% of the energy is stored in the specimen as elastic energy when it reaches the peak stress under static load. The average total energy of water-saturated specimens is 67.55% of that of dry specimens. The average energy dissipation density of water-saturated specimens under 0.3 MPa, 0.4 MPa and 0.5 MPa air pressure is 0.79, 0.91 and 0.92 times of that of dry specimens, respectively. Water-saturated specimens will deteriorate and thus reduce their energy storage and energy absorption effects. The reflected energy, transmitted energy, absorbed energy and incident energy are linear, logarithmic and linear functions, respectively, and the energy absorptivity and specific energy absorptivity of water-saturated specimens are lower than those of dry specimens. Due to the existence of “stefan” effect, the increase of energy dissipation density of water-saturated specimen at high strain rate is greater than that of dry specimen. The mean fractal dimension of water-saturated specimens under 0.3 MPa, 0.4 MPa and 0.5 MPa is 1.09, 1.05 and 1.16 times that of dry specimens. At the same strain rate, the number and width of cracks in water-saturated specimens are larger than that in dry specimens. Water-saturated behavior reduces the energy absorption capacity of tuff, increases the fractal dimension of crack growth, and significantly reduces the resistance of water-saturated rock to external loads.

Experimental and constitutive model investigation on the tensile mechanical properties of polyurea at wide strain-rate range

Polyurea is extensively utilized as a protective coating material for structures under impact and blast loadings, owing to its significant large tensile deformation capability and strain hardening effect. In this study, the tensile performance of polyurea was experimentally and theoretically investigated. Firstly, rational geometric shapes and dimensions were designed, and a series of quasi-static and dynamic uniaxial tensile tests were conducted to obtain the nonlinear stress-strain curves at different strain rates. The results indicated a notable strain-rate effect in polyurea, with an increase in elastic modulus and tensile stress as the strain rate increased. Moreover, as the strain rate escalates, the strain hardening effect becomes more pronounced, thereby enhancing the protective capabilities of polyurea. Subsequently, an existing hyperelastic model, namely the Mooney-Rivlin (MR) model, was modified to incorporate the strain rate effect, resulting in a non-linear visco-hyperelastic constitutive model. Furthermore, the proposed constitutive model and parameters were validated by simulating existing tensile and blast tests using the finite element (FE) program LS-DYNA. This work could provide a reference for the design of structural protection.

Multi-objective optimization and comparison of machine learning algorithms for the prediction of tensile properties of aluminum-magnesium alloy

The aluminum-magnesium (Al-Mg) alloy, widely utilized in the aerospace industry is the focal point of this investigation, which examines the effects of temperature, strain rate, and magnesium concentration on its mechanical attributes. These parameters are crucial for their significant roles in both automotive and aviation applications. Through meticulous examination, this study elucidates the influence of these variables on the alloy's tensile strength and stiffness. Employing response surface methodology, it identifies the optimal conditions under which the alloy demonstrates peak mechanical performance. Further, this research conducts a comprehensive comparison of eighteen machine learning algorithms to determine the most effective predictors for these mechanical properties. It highlights Polynomial Regression and Gradient Boosting Tree as the superior models to accurately forecast strength and stiffness, respectively. Not only does this study address the existing gap in the literature regarding the multi-objective optimization and predictive modeling of Al-Mg alloys' tensile properties but also it exemplifies the integration of molecular dynamics simulations with machine learning techniques in materials science research. The insights garnered from this work offer substantial contributions to industrial applications and foster the advancement of computational investigations into Al-Mg alloys.

The deformation and friction mechanisms of NiFeCr alloys based on molecular dynamics simulations

NiFeCr alloys are widely used in aerospace, marine and power equipment due to their good mechanical properties and wear resistance. At present, the relevant research on NiFeCr alloys mainly focuses on the design and preparation of the alloys, and there are relatively few studies on their mechanical behaviour and scratch deformation. In this paper, the effect of strain rate on the mechanical behaviour and scratch deformation of NiFeCr alloys is investigated using the molecular dynamics method. The results of tensile deformation under different strain rates show that when the strain rate increases from 2.5 × 109/s to 5.0 × 109/s, multiple slip systems are initiated simultaneously, and the entanglement of dislocations in different slip systems leads to dislocation stacking, and the strain rate enhancement effect is significant. When the strain rate is from 5 × 109/s to 7.5 × 109/s, the strain rate enhancement effect is not obvious. Further molecular dynamics scratching studies were carried out, and the results showed that as the scratching rate increased, the strain rate increased, the total number and length of dislocations increased, and the scratching force increased.

Effect of strain rate and temperature on dynamic compressive behavior of HfBeTiZrCuNi high entropy bulk metallic glass

This study investigated the high-temperature dynamic mechanical properties of Hf-based high entropy bulk metallic glass (HE-BMG). Uniaxial dynamic compressive tests of Hf-based HE-BMG were conducted at elevated temperatures (from 298 to 800 K) under a high strain rate (from 1000 to 5000 s−1) by a split Hopkinson pressure bar (SHPB) device with a high-temperature system, and the failed specimens were analyzed in terms of microstructures and fracture modes. The dynamic test results show that the maximum compressive stress and the total strain decrease with increasing strain rate and temperature, exhibiting significant strain rate and temperature sensitivity. Three different fracture modes were observed with increasing strain rates, while heating the temperature could promote the transition process of the fracture modes. When the adiabatic or heating temperature reaches above the crystallization temperature, the embrittlement caused by metallic glass crystallization makes the fracture mode change. The mechanical behavior of Hf-based HE-BMG at high temperatures and high strain rates could be attributed to the combination of adiabatic heating and embrittlement.

Particle breakage of calcareous sand from low-high strain rates

The influence of strain rate on the mechanics of particles is well documented. However, a comprehensive understanding of the strain rate effect on calcareous particles, particularly in the transition from static to dynamic loading, is still lacking in current literature. This study conducted 720 quasi-static and impact tests on irregular calcareous particles to investigate the macroscopic strain rate effect, and performed numerical simulations on spherical particles to explore the underlying microscopic mechanisms. The strain rate effect on the characteristic particle strength was found to exhibit three regimes: in Regime 1, the particle strength gradually improves when the strain rate is lower than approximately 102 s−1; in Regime 2, the particle strength sharply enhances when the strain rate increases from 102 s−1 to 104 s−1; and in Regime 3, the particle strength remains almost constant when the strain rate is higher than 104 s−1. The three-regime strain rate effect is an inherent property of the material and independent of particle shape. The asynchrony between loading and deformation plays a dominant role in these behaviors, leading to a thermoactivation-dominated effect in Regime 1, a macroscopic viscosity-dominated effect in Regime 2, and a combined thermoactivation and macroscopic viscosity-dominated effect in Regime 3. These mechanisms induce a transition in the failure mode from splitting to exploding and then smashing, which increases the energy required to rupture a single bond and, consequently, enhances the particle strength.

Dynamic deformation behavior of single phase VNbTa medium-entropy alloys

In this study, the deformation behavior of body-centered-cubic (BCC) VNbTa medium-entropy alloy (MEA) was studied under different strain rates ranging from 10−3 s−1 to 5000 s−1 using screw-driven testing machine and split Hopkinson pressure bar (SHPB), respectively. The alloy presents an outstanding synergy of strength and plasticity without any adiabatic shear bands even at a strain rate of 5000 s−1. Moreover, the yield strength of the alloy displays an obvious strain rate dependence, increasing by ∼94.4% from 842 MPa at 10−3 s−1 to 1637 MPa at 5000 s−1. The strain rate sensitivity (SRS) factor m and highest temperature rise under dynamic loading is calculated to be 0.2991 and 182 K, respectively, which means a strong strain rate hardening and thermal softening resistance. Microstructure evolution analyses demonstrate a transition of deformation mechanism from single dislocation slip controlling in low strain rate to a synergy of mechanical twinning and dislocation slip in high strain rate. Therefore, the excellent dynamic mechanical properties could be attributed to the synergistic effects of the strong strain rate hardening and thermal softening resistance, the mechanical twins, and the cell structures and microbands derived from dislocation slip controlling. In addition, the dynamic deformation behavior of VNbTa could also be described by a classical Johnson-Cook model. Combining the excellent cryogenic temperature mechanical properties (tensile strength of ∼1930 MPa and fracture elongation ∼27%), the present work further indicates that the VNbTa MEA has great potential for engineering applications under some extreme circumstances.

Research on damage behavior of silicone rubber under dynamic impact

Viscoelastic rubber materials are widely used in various vibration reduction structures of military and construction machinery. The complex driving and working conditions make the mechanical structure suffer severe impact, which leading to the damage or lose efficacy of the important viscoelastic elements. In order to reveal the dynamic mechanical properties of silicone rubber after impact, the Uniaxial compression tests of silicone rubber under different high strain rates were carried out with the separated Hopkinson pressure bar (SHPB) dynamic impact experiment, and the original Zhu-Wang-Tang (ZWT) constitutive model was modified by combining logarithmic law and power function law. The dynamic impact simulation model of silicone rubber was established using the modified ZWT-rate-dependent constitutive model, and the dynamic impact damage behavior of silicone rubber was studied under the condition of high strain rate, and the microscopic damage analysis was carried out on the experimental silicone rubber samples by scanning electron microscopy (SEM). The results show that the silicone rubber has obvious strain rate effect and strong deformation resistance at high strain rate. The modified ZWT-rate-dependent constitutive model can be used to obtain the constitutive expression of unified parameters, which can better describe the dynamic mechanical properties of silicone rubber at high strain rates. After dynamic impact compression, a damage line zone appears in the silicone rubber sample. There is a certain rule between the position of the line zone and the loading strain rate and the friction coefficient of the end face, and the silicone rubber is significantly affected by the friction effect of the end face.

Hot deformation and dynamic recrystallisation behaviour of Fe-23Mn-3Cr-0.3C steel

The effects of deformation temperature (880–1200°C) and strain rate (0.001–1 s−1) on the hot deformation mechanism of Fe-23Mn-3Cr-0.3C steel were investigated through single-pass compression tests. The findings revealed that the flow stress of Fe-23Mn-3Cr-0.3C steel could be accurately represented by a constitutive equation based on the Arrhenius equation, with a high correlation coefficient of 0.996 observed between experimental values and the model. Moreover, a critical strain model for dynamic recrystallisation (DRX) was formulated. The study delved into the evolution of DRX using electron backscatter diffraction (EBSD) technology, uncovering two primary nucleation mechanisms: (1) discontinuous DRX characterised mainly by grain boundary bulging and twin-assisted nucleation and (2) continuous DRX characterised predominantly by sub-grain rotation.

Dynamic compressive behavior of functionally graded triply periodic minimal surface cellular structures

The Triply Periodic Minimal Surface (TPMS) structure is regarded as a porous structure used for impact protection due to its lightweight, high strength, and high specific energy absorption (SEA). This paper investigates the dynamic mechanical properties of the TPMS structure by Split Hopkinson Bar (SHPB) experiments and finite element analysis (FEA). We compare stress peak, SEA, strain rate effect, and deformation pattern for functionally graded Primitive (P), uniform P, and uniform Gyroid (G) structures. It is found that the increasing magnitude of peak stress in the TPMS structures becomes more evident under high-impact loads. As the relative density increases, the strain rate effect becomes more prominent. The uniform G structures exhibit higher plateau stress and SEA than uniform P structures. Besides, graded P structures exhibit a climbing phenomenon compared to uniform P structures in the platform section. The FEA results also demonstrate that higher SEA and plateau stresses are exhibited in the graded P structure. The graded design minimizes the strain rate effect compared to the corresponding uniform structures. It is essential to set a properly graded index to enhance the dynamic energy absorption capacity of the TPMS structure, as more fluctuations occur when the graded index increases.

Dynamic Mechanical Properties and Modified Material Constitutive Model for Hot Forged Ti2AlNb over Wide Ranges of Temperature and Strain Rate.

In this paper, the stress-strain curves of Ti2AlNb are established based on uniaxial impact tests over wide ranges of temperature and strain rate. The Ti2AlNb exhibited the work hardening effect but did not show an obvious yield stage during a quasi-static compression test. In the SHPB test, an obvious temperature softening effect was found, the strain rate strengthening effect was detected when the strain rate was 4000-8000 s-1, and the strain rate softening effect was detected in the range of 8000-12,000 s-1. A function describing the effect of strain rate on the strain rate strengthening parameters under various temperatures was proposed to modify the basic J-C constitutive model. The relative errors between the experimental measured value and predicted values in various experimental conditions with a modified J-C model were less than 5.0%. The results verified that the modified J-C model could accurately describe the dynamic mechanical properties of Ti2AlNb at high temperatures and strain rates. The research could help to illustrate the cutting mechanism and finite element simulation of Ti2AlNb alloy.

Effects of strain rate and bedding on shale fracture mechanisms

Anisotropic shale is commonly distributed in nature and undergoes both dynamic compressive and tensile load in geological engineering. In this article, the coupling effects of strain rate and bedding structures on the fracture mechanisms of shale are investigated using a split Hopkinson pressure bar (SHPB) system. The tension–compression comparative study is conducted. The Brazilian disc method is modified, and a unified strain rate measurement method is established to comprehensively analyze shale’s fracture-related properties, including moduli, strength and energy dissipation. The results indicate that the energy dissipated by shale fracture is strongly related to its strength. The strain rate and bedding affect the anisotropic strength and dissipated energy by changing the crack density and crack propagation mode. At low or medium strain rates, the bedding orientation of shale determines the direction of crack propagation. However, at high strain rates, microcracks in different directions are widely activated in the shale, which increases the fracture degree and decreases the difference in fracture toughness between the shale’s matrix and bedding planes. This also leads to a decrease in anisotropy and causes the bedding planes to lose control over the direction of crack propagation. Additionally, the dynamic tensile strength of shale increases faster than the compressive one with the strain rate, leading to a reduction in the proportion of tensile failure under impact load. Based on the experimental findings, a new anisotropic damage constitutive model is developed to characterize the dynamic properties of shale. This model reflects the anisotropic damage evolution behaviors and aligns well with experimental results, offering a theoretical foundation for predicting shale’s dynamic fracture behavior. In addition to shale, the developed experimental methods and theoretical models can also be applied to the fracture analysis of other brittle transversely isotropic materials.

Effect of Strain Rate on Mechanical Deformation Behavior in CuZr Metallic Glass.

Tensile tests were performed on Cu64Zr36 metallic glass at strain rates of 107/s, 108/s, and 109/s via classical molecular dynamics simulations to explore the underlying mechanism by which strain rate affects deformation behavior. It was found that strain rate has a great impact on the deformation behavior of metallic glass. The higher the strain rate is, the larger the yield strength. We also found that the strain rate changes the atomic structure evolution during deformation, but that the difference in the atomic structure evolution induced by different strain rates is not significant. However, the mechanical response under deformation conditions is found to be significantly different with the change in strain rate. The average von Mises strain of a system in the case of 107/s is much larger than that of 109/s. In contrast, more atoms tend to participate in deformation with increasing strain rate, indicating that the strain localization degree is more significant in cases of lower strain rates. Therefore, increasing the strain rate reduces the degree of deformation heterogeneity, leading to an increase in yield strength. Further analysis shows that the structural features of atomic clusters faded out during deformation as the strain rate increased, benefiting more homogeneous deformation behavior. Our findings provide more useful insights into the deformation mechanisms of metallic glass.

FCA-based efficient prediction of effective properties for 3D braided composites considering the effect of strain rate

The existing fast concurrency algorithms are difficult to predict the dynamic mechanical performance of three-dimensional (3D) braided composites from different scales. A modified Finite Element Method Cluster Analysis (FCA) method is employed to address this challenge. The modified FCA method is consisted of an offline and an online stage. In the offline stage, the high-fidelity Representative Unit Cell (RUC) is compressed to form a cluster-based RUC via the k-means method. Additionally, the cluster interaction matrix is calculated. In the online stage, the cluster interaction matrix is updated according to the strain rate levels for predicting the stress–strain curves for the RUC. Based upon the comparison with the data obtained from the Split Hopkinson Pressure Bar (SHPB) experiments, it is found that the modified FCA method can accurately predict the stress–strain curves under different strain rates for RUCs. Additionally, the modified FCA method provides a great improvement on computing efficiency when predicting the dynamic behavior of 3D braided composites.

Ballistic performance of flexible structures composed of UHMWPE fibers and airbag: Effects of the stacking order

A series of flexible structures incorporating an airbag and ultra-high molecular weight polyethylene (UHMWPE) fiber panels were designed as temporary architectures to offer both ballistic protective functions and lightweight constructions. Three primary structural configurations, monolithic structures (airbag or UHMWPE panel alone), bi-layer structures (airbag/ UHMWPE panel and UHMWPE panel/airbag), and sandwich structures (UHMWPE panel/airbag/ UHMWPE panel) were tested. A T12A carbon tool steel sphere with the diameter of 12.7 mm was utilized as the ballistic threat within an impact velocity range of 0–500 m/s. Investigations into the effect of stacking order on ballistic performance were carried out experimentally and numerically. The failure characteristics, ballistic limits, energy dissipations, impact processes and interaction effects of these structures are discussed. To facilitate the establishment of numerical models for impact analysis using ABAQUS, a material constitutive model of thermoplastic polyurethanes (TPU) including strain rate effect was developed. The numerical models of the monolithic single-sheet UHMWPE panel and airbag for impact analysis were subsequently verified by experiments in terms of impact processes and ballistic limits. The results reveal that arranging a few layers of UHMWPE panels in front of the airbag can improve the collapse ballistic limit while maintaining the failure ballistic limit. The inclusion of an airbag reduces the energy dissipation efficiency of composite structures. The potential to enhance ballistic protection through the combination of airbags and UHMWPE panels is highlighted. Stress dispersion and deformation restraint are identified as significant factors influencing the ballistic performance of the composite structures.

Experimental study on dynamic direct tensile performances of steel fiber-reinforced RPC at high strain rates

Reactive power concrete (RPC) exhibits excellent mechanical properties, makes it great potential for applications. RPC has gained increasing attention in academic and engineering areas and has been used in fields such as anti-explosion engineering. The insufficient tensile strength of RPC is one of the critical reasons for its structural failure. Existing studies revealed that the strain rate effect of concrete under dynamic tension is stronger than that under dynamic compression. The existing research focuses either on dynamic splitting and spalling tests, or dynamic uniaxial tensile properties with a strain rate of 0–100/s, neither of which are representative of the effect of RPC subject to explosion. In addition, the study of the dynamic uniaxial tensile constitutive model of RPC has not been reported in the existing research. To solve the existing limitations, this study conducted dynamic direct tension tests on steel fiber-reinforced RPC with a predefined strain rate higher than 100 s−1 using a Split Hopkinson Tension Bar (SHTB) apparatus. RPC dumbbell-shaped samples, including plain RPC and steel fiber-reinforced RPC (SFRPC) with 1 % and 2 % fiber volumetric fractions, were tested at high strain rates of 98–528 s−1. Based on the test results of this study and those derived from existing publications, the relationship between dynamic direct tensile properties, steel fiber fraction, and strain rate was quantitatively analyzed, and corresponding empirical formulae were proposed. To meet the demand for numerical analysis on RPC structures subjected to explosive forces, a dynamic tensile stress-strain model for steel fiber-reinforced RPC considering steel fiber, strain rate, and dynamic toughness, was established.

A meshless computational framework for studying cold spray additive manufacturing including large numbers of powder particles with diverse characteristics

Cold spray (CS) has emerged as an appealing additive manufacturing (AM) technique for producing or repairing individual components or entire structures. Compared to fusion-based AM technologies, cold spray additive manufacturing (CSAM) offers distinct advantages in the fabrication of components, while avoiding some melting/solidification-related issues such as phase transformation and oxidation. It involves intricate processes that pose significant challenges for numerical modeling, particularly when simulating the entire process at a large scale. The smoothed particle hydrodynamics (SPH) method is highly suitable for handling large material deformations due to its Lagrangian and meshless nature. In this work, we develop an enhanced SPH method to conduct large-scale simulations of CSAM with different powder sizes, morphologies, and distributions. A modified material model has been incorporated to accurately capture the strain-rate hardening effects during the plastic stage. The computational scale is greatly improved by using a Message Passing Interface (MPI) based framework, enabling the simulation of approximately ten million SPH particles. To the authors’ knowledge, this study marks the first attempt to numerically reproduce the entire process of CSAM with real powder sizes and distributions. Experimental data measured for a wide range of powder velocities are used to validate the simulation results and assess the prediction accuracy. Subsequently, we comparatively study the bonding mechanisms of powders with the same or different sizes, while also identifying a four-stage coating process. The effects of powder morphology on the bonding process are thoroughly investigated. A large-scale CSAM process is finally reproduced to demonstrate the capability of the present meshless scheme, and mechanisms of pore formation are analyzed, providing valuable insights for practical engineering applications.

Effects of Quasi-Static Strain Rate and Temperature on the Microstructural Features of Post-Processed Microstructures of Laser Powder Bed Fusion Ti6Al4V Alloy

This study documents an investigation of the flow stress properties and microstructural features of Ti6Al4V (ELI) alloy produced using laser powder bed fusion (LPBF). Selected heat treatment strategies were applied to the material to obtain different microstructures. The influence of quasi-static strain rates and temperature on the obtained microstructures of this material and their strain hardening properties are documented in this study. All microstructures of the alloy formed in this study were found to be sensitive to quasi-static strain rates and temperatures, where their flow stresses increased with increasing strain rate and decreased for tests conducted at elevated temperatures. The strain hardening rates of the fine microstructures were found to be high compared to those of coarse microstructures. The strain hardening rates for the various forms of LPBF Ti6Al4V (ELI) examined here were found to diminish with increasing test temperature. Though the deformed surfaces of the built samples were largely dominated by adiabatic shear bands (ASBs), the absence of ASBs was noted for all samples tested at a temperature of 500 °C and an imposed strain of 30%.

Dynamic splitting behavior of microcapsule-based self-healing cementitious composites under SHPB impact loading

This study presents an experimental study on the dynamic splitting tensile performance of microcapsule-based self-healing cementitious composites and fiber-reinforced microcapsule cementitious composites. The research aims to determine the effect of microcapsule dosages, fiber types, and strain rates on the dynamic splitting tensile behavior of materials. A total of 99 specimens were subjected to the split Hopkinson pressure bar (SHPB) impact loading within the strain rates of 0.85–17.12 s−1. A high-speed camera was employed to capture the crack propagation process, and scanning electron microscopy (SEM) was used to characterize the corresponding microstructure. The results indicated that the splitting tensile performance of materials exhibits significant strain rate sensitivity. The addition of microcapsules increases the dynamic splitting tensile strength of the material, and the highest energy absorption capacity can be achieved with a 5 % microcapsule dosage. The incorporation of polyvinyl alcohol (PVA) and polyethylene (PE) fibers effectively enhances dynamic splitting tensile strength and energy absorption capacity, achieving optimal performance with the incorporation of PVA-PE hybrid fibers. Furthermore, the investigation of the dynamic increase factor (DIF) of the material indicates that fibers heighten the strain rate sensitivity of the material.