Dynamic Behavior Of Materials Research Articles

Comprehensive study of projectile impact on lightweight adobe masonry

We conduct a comprehensive experimental and numerical study of the impact response of lightweight adobe masonry with a density of 1.2 g/cm3. Based on two independent test cases, a simulation model for lightweight adobe is validated and applied. First, we investigate the impact of a spherical projectile on finite and semi-infinite targets. Then, the penetration behavior of a generic hollow projectile is studied. In each case, the data from the ballistic experiments is compared to the results of corresponding numerical simulations. The employed numerical model utilizes a p-α-equation of state, recently derived from planar plate impact experiments on the same lightweight adobe material [Sauer et al., Journal of Dynamic Behavior of Materials 4 (2018) 231–243]. Strength and failure modeling are based on a validated numerical description of another adobe material that has a density of 1.8 g/cm3. The simulation model for lightweight adobe is capable of simultaneously reproducing all experimental results in a quantitatively appropriate way. This reveals that, although the phenomenology and quantitative properties differ significantly, lightweight adobe (1.2 g/cm3) and adobe (1.8 g/cm3) can be described by the same approach. Hence, this work suggests that the utilized model is applicable for analyses of impact loading of the entire class of adobe materials.

A unified experimental-theoretical approach to predict the critical stress characteristics of failure and yielding under quasi-static and dynamic loading

The results of experimental and theoretical studies on the dynamic response of brittle and ductile materials are presented. The work shows the possibility of predicting the critical stress of brittle materials or yield strength of ductile materials over a wide range of strain rates on the basis of a combination of a simple theoretical approach to dynamic strength and a set of experimental data obtained using a conventional technique. The studies were carried out using fine-grained concrete and ceramic brick as representatives of brittle materials, and copper and titanium as representatives of ductile materials. The traditional Kolsky method was used to determine the strength and ductility characteristics under dynamic loading conditions of the experimental samples. The sensitivity of the critical stress characteristics of failure and yielding of the studied materials to the strain rate is shown. The incubation time approach is used to interpret the effects of strain rate. The applicability of the incubation time criterion to prediction of the dynamic behaviour of both brittle and ductile materials is shown. The presented unified experimental-theoretical approach can be applied in engineering practice to model the dynamic response of structural materials.

Experimental and analytical investigation of the dynamic behavior of granular base course materials used for China's high-speed railways subjected to freeze-thaw cycles

With the rapid development of high-speed railways (HSRs) in seasonally frozen regions in China in recent years, there is an increasing need for better understanding of how the construction materials behave. In particular, the dynamic behavior of granular base course materials used for China's HSRs subjected to combined actions of cyclic loading and freeze-thaw (F-T) cycles has attracted much attention. In this study, a series of cyclic triaxial tests were performed to investigate the characteristics of granular base course materials. A number of factors including effect of F-T cycles were considered in these tests. As such, representative test results of dynamic shear stress amplitude (τ¯d), dynamic shear modulus (Gd), and damping ratio (λ) are presented and discussed. Based on the Hardin-Drnevich model, a fitting equation for determining maximum dynamic shear modulus (Gd,max) is proposed. Then, a unified normalized dynamic shear modulus (Gd/Gd,max) curve is drawn and well validated by the test results. Furthermore, equations for λ are expressed in terms of an exponential function of Gd/Gd,max. The test results show that the Gd/Gd,max curves are not completely consistent with previous studies. Overall, this study provides further insights into the dynamic behavior of granular base course materials subjected to F-T cycles.

Meshfree analysis on dynamic behavior of hard brittle material in abrasive flow machining

Erosion mechanism of hard brittle target subjected to abrasive particles has been investigated numerically in the present study. A coupled model based on smoothed particle hydrodynamics and finite elements was established. The large deformation and high strain rate of eroded material were concerned by using a strain rate-dependent constitutive model. Dynamic processes of material deformation and fracture growth were analyzed. The results indicated that the radial and lateral cracks were the main fracture modes of aluminum nitride target material. Moreover, the effects of different incident parameters such as impact angle and velocity on erosion mechanism were also investigated.

Explicit dynamic fracture simulation of two-phase materials using a novel meso-structure modelling approach

In order to reduce the experimental cost and enable the numerical modelling better approaches the actual meso-structures of two-phase materials, a novel meso-scale modelling approach, combining the image-based and the parameterized modelling approaches, has been presented. In this approach, only limited samples of the studied two-phase material need to be provided for establishing an aggregate library, through which finite element models with different spatial distributions and volume fractions of aggregate can be arbitrarily generated for the use of virtual test. In the present virtual test, fracture failures were simulated in the framework of explicit dynamics. A rate-dependent cohesive zone model (CZM) was implemented through the user subroutines in ABAQUS to characterize the dynamic damage and fracture of the meso-structures. At the same time, an algorithm of embedding cohesive elements automatically into the potential damage zones was put forward. Finally, two typical numerical examples were given to verify these proposed methods and models, meanwhile the influences of spatial distribution and volume fraction of aggregate on the mechanical performance of the meso-structure were investigated. It can be validated that the present developed methods and models can effectively and efficiently characterize the dynamic fracture behavior of two-phase materials.

Dynamic behavior of BiVO4 material under mechanical studies

The mechanical relaxation technique is applied to investigate the fundamental dynamic behavior of BiVO4 material. A prominent internal friction peak is observed around 430 K at 1 Hz, which is actually composed of three sub-peaks (P1, P2 and P3 from low to high temperature). And the associated modulus anomalies can also be found in any of the samples. The peak P1 with activation energy E1 ∼ 3.20 eV is probably related to the stress-induced unequal positions of Bi3+ ions; while the main P2 peak with E2 = 0.91 eV is associated with a complex mechanism, which originates from the viscous motion of domain walls and the interaction of domain walls with oxygen vacancies; and the responsive P3 peak is resulted from the ferroelastic–paraelastic phase transition, accompanied by a minimum modulus value. Based on the relaxation process and crystalline structure of BiVO4, the motion model of ferroelastic domain walls and transport mechanism of diffusion are suggested. Our results pave the way for better understanding the intrinsic dynamic and multifunctional properties of BiVO4.

Unlocking the significant role of shell material for lithium-ion battery safety

The cylindrical lithium-ion battery has been widely used in 3C, xEVs, and energy storage applications and its safety sits as one of the primary barriers in the further development of its application. Among all cell components, the battery shell plays a key role to provide the mechanical integrity of the lithium-ion battery upon external mechanical loading. In the present study, target battery shells are extracted from commercially available 18,650 NCA (Nickel Cobalt Aluminum Oxide)/graphite cells. The detailed material analysis is conducted to reveal a full understanding of the material. Then, the dynamic behavior of the battery shell material is experimentally investigated. Both theoretical constitutive and numerical models have been developed, capable to describe mechanical behaviors of the battery shell material upon impact loading. It is the first time to discover that the strain rate effect of the shell material shall be considered for the mechanical integrity of the battery and high strength of the shell material may contribute to an early short-circuit triggering. The quantitative relationship is also established between short-circuit and material strength. Results lay a solid foundation towards providing a theoretical safety design guidance for the shell material choice of cylindrical lithium-ion batteries.

Unraveling the Effect of Material Properties and Geometrical Factors on Ballistic Penetration Energy of Nanoscale Thin Films

It is crucial to investigate the dynamic mechanical behavior of materials at the nanoscale to create nanostructured protective systems that have superior ballistic impact resistance. Inspired from recent experimental advances that enable ballistic materials testing at small scales, here we report a comparative analysis of the dynamic behavior of nanoscale thin films made from multilayer graphene (MLG), polymer, gold, and aluminum under high-speed projectile impact. We employ atomistic and coarse-grained (CG) molecular dynamics (MD) simulations to measure the ballistic limit velocity (V50) and penetration energy (Ep) of these nanoscale films and investigate their distinctive failure mechanisms over a wide range of impact velocities (Vi). For the local penetration failure mechanism observed in polymer and metal films, we find that the intrinsic mechanical properties influence Ep at low Vi, while material density tends to govern Ep at high Vi. MLG films uniquely show a large impact propagation zone (IPZ), which transfers the highly localized impact energy into elastic deformation energy in a much larger area through cone wave propagation. We present theoretical analyses that corroborate that the size of IPZ should depend not only on material properties but also on a geometrical factor, specifically, the ratio between the projectile radius and film thickness. This study clearly illustrates how material properties and geometrical factors relate to the ballistic penetration energy, thereby allowing a quantitative comparison of the nanoscale ballistic response of different materials.

DEM/FEM simulation for impact response of binary granular target and projectile

Three-dimensional dynamic discrete element method (DEM) and finite element method (FEM) simulation using LS-DYNA were, respectively, applied to the randomly distributed binary granular material and to the cylindrical projectiles in order to clarify the effect of size distribution of target particles on the dynamic behaviour of low density granular material. It was found that the peak resistance force of projectile during penetration depends on the packing density of the granular materials and on the impact velocity of projectile. The change of resistance force was well understood in connection with the propagation and the reflection of stress wave in projectile. The variety of particle size almost did not affect the resistance force of projectile. Densified region in granular material was generated ahead of projectile after impact. The densified region propagated in the depth direction and its propagation speed depended on the packing density of target granular material and impact velocity of projectile. That is, projectile impact behaviours of granular materials can be uniformly handled by impact velocity and packing density of the granular material, not depending on the variety of the particle size.

Wet/dry influence on behaviors of closed-cell polymeric cross-linked foams under static, dynamic and impact loads

Polymeric materials have been used as critical components in a wide range of engineering structures in built environments. The superior characteristics of polymeric materials have led to various applications such as energy absorber during shock or impact events, lightweight structures, and thermal insulation. The key benefit is derived from relatively lower weight and density in comparison with other materials. The emphasis of this study is placed on closed-cell polymeric material, which is flexible and can potentially be manufactured as a rubber mat for railway track applications. A critical literature review reveals that the dynamic behavior of closed-cell polymeric material has not been fully investigated, especially when the materials are usually exposed to water. We are the first to present the wet/dry influences on the characteristics of closed cell cross-linked polyethylene foam under static, dynamic and shock loads. In our study, the water absorption and swelling of the materials are measured after 24 h of immersion in de-ionized water. Static, dynamic, and impact loading are applied to closed-cell polymeric materials on both wet and dry states. The behaviors and responses of the materials can inform whether or not a closed-cell polymeric material can be used as under ballast mats and under sleeper pads in railway tracks under operational environments. Based on our results, it is found that this closed-cell-polymeric material is not suitable for use as under sleeper pads. However, they have reasonably strong potential for use as under ballast mats under various rail operational parameters.

Prediction of mechanical properties of PP/EVA polymer blends governed by EVA phase change in the presence of environmentally‐friendly inorganic tungsten disulfide nanotubes (INT‐WS2)

Anticipating dynamic mechanical behavior of polymeric materials over long period of time and under different frequencies is the first step to be taken to afford load‐bearing applications. Nevertheless, what we know about dynamic mechanical behavior of polymers is only limited to experiments, which necessitates large pools of data spending too much money, time, and energy. Environmentally‐friendly inorganic tungsten disulfide nanotube (INT‐WS2), was introduced to polypropylene/ethylene vinyl acetate copolymer (PP/EVA, 75/25 wt/wt) blends through melt mixing, and dynamic mechanical analysis (DMA) frequency sweep tests were performed to obtain master curves based on time‐temperature superposition (TTS) theorem. The influence of EVA phase change (solid, semi solid, and melt domains) on the creep and recovery behavior of nanocomposites in linear region was then studied. It was found that using INT‐WS2 along with PP‐g‐MA results in distinctive improvement in creep‐recovery response of nanocomposites. Burger and Weibull models were used to mimic viscoelastic behavior of the nanocomposites. Creep compliance master curves predicted creep compliance, while analysis of cyclic creep‐recovery at 30 °C revealed almost constant permanent strain parameters for sample having 5 wt% INT‐WS2 and PP‐g‐MA after three times repeating test cycles. Influence of phase change phenomenon of EVA domains on creep‐recovery behavior of nanocomposites was mechanistically demonstrated. POLYM. COMPOS., 40:1964–1978, 2019. © 2018 Society of Plastics Engineers

Conducting Elevated Temperature Normal and Combined Pressure-Shear Plate Impact Experiments Via a Breech-end Sabot Heater System.

A novel approach for conducting normal and/or combined pressure-shear plate impact experiments at test temperatures up to 1000 °C is presented. The method enables elevated temperature plate-impact experiments aimed towards probing dynamic behavior of materials under thermomechanical extremes, while mitigating several special experimental challenges faced while performing similar experiments using the conventional plate impact approach. Custom adaptations are made to the breech-end of a single-stage gas-gun at Case Western Reserve University; these adaptations include a precision-machined extension piece made from SAE 4340 steel, which is strategically designed to mate the existing gun-barrel while providing a high tolerance match to the bore and keyway. The extension piece contains a vertical cylindrical heater-well, which houses a heater assembly. A resistive coil heater-head, capable of reaching temperatures of up 1200 °C, is attached to a vertical stem with axial/rotational degrees of freedoms; this enables thin metal specimens held at the front-end of a heat-resistant sabot to be heated uniformly across the diameter to the desired test temperatures. By heating the flyer plate (in this case, the sample) at the breech-end of the gun-barrel instead of at the target-end, several critical experimental challenges can be averted. These include: 1) severe changes in the alignment of the target plate during heating due to the thermal expansion of the several constituents of the target holder assembly; 2) challenges that arise due to the diagnostics elements, (i.e., polymer holographic gratings, and optical probes) being too close to the heated target assembly; 3) challenges that arise for target plates with an optical window, where crucial tolerances between the sample, bond layer, and window become increasingly difficult to maintain at high temperatures; 4) in the case of combined compression-shear plate impact experiments, the need for high-temperature resistant diffraction gratings for the measurement of transverse particle velocity at the free surface of the target; and 5) limitations imposed on the impact velocity necessary for unambiguous interpretation of the measured free surface velocity versus time profile due to thermal softening and possibly yielding of the bounding target plates.By utilizing the adaptations mentioned above, we present results from a series of reverse geometry normal plate impact experiments on commercial purity aluminum at a range of sample temperatures. These experiments show decreasing particle velocities in the impacted state, which are indicative of material softening (decrease in post-yield flow stress) with increasing sample temperatures.

Micro-mechanical numerical analyses on the effect of stress state on ductile damage under dynamic loading conditions

Abstract The paper deals with the effect of stress state on the dynamic damage behavior of ductile materials. The rate- and temperature-dependent continuum damage model has been enhanced to take into account the influence of the stress triaxiality and the Lode parameter on damage condition and on rate equations of damage strains. Different branches of these criteria depending on the current stress state are considered based on different damage and failure processes on the micro-level. To get more insight in the dynamic damage and fracture processes micro-mechanical behavior of void-containing representative volume elements have been analyzed numerically. These three-dimensional numerical simulations based on different dynamic loading conditions take into account a wide range of stress states in tension, shear and compression domains. Based on the numerical results general trends of dynamic damage and failure behavior can be shown and stress-state-dependent equations for damage criteria and for the formation of damage strains can be proposed.

Parallel SPH modeling using dynamic domain decomposition and load balancing displacement of Voronoi subdomains

A highly adaptive load balancing algorithm for parallel simulations using particle methods, such as molecular dynamics and smoothed particle hydrodynamics (SPH), is developed. Our algorithm is based on the dynamic spatial decomposition of simulated material samples between Voronoi subdomains, where each subdomain with all its particles is handled by a single computational process which is typically run on a single CPU core of a multiprocessor computing cluster.The algorithm displaces the positions of neighbor Voronoi subdomains in accordance with the local load imbalance between the corresponding processes. It results in particle transfers from heavy-loaded processes to less-loaded ones. Iteration of the algorithm puts into alignment the processor loads. Convergence to a well-balanced decomposition from imbalanced one is improved by the usage of multi-body terms in the balancing displacements.The high adaptability of the balancing algorithm to simulation conditions is illustrated by SPH modeling of the dynamic behavior of materials under extreme conditions, which are characterized by large pressure and velocity gradients, as a result of which the spatial distribution of particles varies greatly in time. The higher parallel efficiency of our algorithm in such conditions is demonstrated by comparison with the corresponding static decomposition of the computational domain. Our algorithm shows almost perfect strong scalability in tests using from tens to several thousand processes.

Investigation on static and dynamic corrosion behaviors of thermal energy transfer and storage system materials by molten salts in concentrating solar power plants

With the emergence of the concentrating solar power (CSP) technology, the corrosion behaviors of potential materials applied in thermal energy transfer and storage system attract tremendous attentions. Corrosion behaviors of X80 carbon steel, 304, 316L stainless steels, and 600, 825 nickel alloys in the molten salt mixtures at different temperatures were comparatively investigated using immersion tests under static and dynamic states and electrochemical scans. The corrosion resistance of stainless steels and nickel‐based alloys in molten salt at 530 °C followed the sequence of 304<316L<600<825. The aggressiveness of different molten salt mixtures was compared, indicating that the ternary system was more aggressive than the binary system. The corrosion aggressiveness under dynamic state was more severe when compared to that under the static state. The N2 atmosphere was proved to be protective for alloys immersed in high temperature molten salts.

Role of Impurities in the Kinetic Persistence of Amorphous Calcium Carbonate: A Nanoscopic Dynamics View

Amorphous calcium carbonate is found in the early stages of biomineral formation. Its moldability and its kinetic persistence against crystallization make it of potential interest to the development of biomimetic materials. The presence of water and of inorganic impurities such as Mg2+ has been reported to increase its kinetic stability. Yet, the precise mechanisms of stabilization as well as the link between structural dynamics and crystallization kinetics are still missing. Here, we report the vibrational and diffusive dynamics of water and other atomic constituents in a series of Mg2+-doped solid amorphous calcium carbonates revealed using coherent X-ray and incoherent neutron scattering. This unique combination of techniques presents a novel view on the nanoscopic dynamic behavior of these amorphous materials: the presence of Mg2+ results in a higher frequency of structural rearrangements within the material. However, this increased dynamic behavior does not translate into a higher crystallization kin...

Flexural fracture mechanisms and fatigue behaviors of Bi4Ti3O12-based high-temperature piezoceramics sintered at different temperatures

In this paper, a series of Aurivillius phase Bi4Ti2.95W0.05O12.05 + 0.2 wt% Cr2O3 (ab. BTWC) ceramics were prepared by a solid-reaction process and sintered at different temperatures (1050 ℃~1150 ℃), their microstructures, fracture mechanisms and fatigue behaviors were investigated under three-point-bending mode. The results show that the grain size of BTWC ceramics increases with increasing the sintering temperature. The typical transgranular mode dominates the fracture behavior of the samples sintered at lower temperatures, while the intergranular fracture can be also observed in the samples sintered at higher temperatures. Besides, the storage modulus (E’) and mechanical loss (tanmδ) of BTWC ceramics have a subtle variation with the increase of sintering temperature. In addition, the high-temperature environment could not only decrease the fracture toughness and bending strength of ceramics but also change their fracture mode. On the other hand, the bending strength also decreases with the decrease of loading rates, which could be attributed to the slow crack growth referring to the dynamic fatigue behavior of brittle materials. The slow crack growth parameter (n) of BTWC ceramics shows a downtrend with increasing their sintering temperature, indicating that those high temperature sintering samples possess a higher susceptibility when subjected to the long-term stress corrosion. Furthermore, the sample sintered at 1125 ℃ exhibits an excellent fatigue resistance when subjected to the cyclic stress. The corresponding fatigue mechanism is not only related to the ferroelectric domain configuration but also involved with the pores or impurities.

A New Multiaxial Specimen for Determining the Dynamic Properties of Adhesive Joints

Adhesive joints are increasingly employed for bonding critical parts of industrial structures. Therefore, adhesive joints become a key element in design, and their mechanical characterization is of the utmost importance. Significant advancement has been realized for their characterization under quasi-static loadings; however characterization techniques are rather limited for dynamic loadings. Indeed, due to the complex paths of waves through structures, existing dynamic characterization techniques will not characterize only the adhesive joint, but instead will characterize the complete assembly containing the joint and the adherents. Moreover, multiaxiality control of the loading on the adhesive joint is difficult to achieve. This paper proposes an innovative experimental technique for the characterization of adhesive joints under dynamic multiaxial loadings. The experimental method relies on three main components: i) a conventional split Hopkinson pressure bar (SHPB) apparatus, ii) a novel specimen, denoted as DODECA, which enables testing of three distinct multiaxial loadings using the same method and iii) local strain and stress measurements performed by digital image correlation (DIC). The paper describes all steps of the experimental procedure, including the underlying preparation of the specimen and the measuring methods. The stress and strain in the adhesive joint are estimated directly from the experimental data both during loading and at the failure point. Finally, the dynamic material behavior of the adhesive joint is identified from the data.

Dynamic behaviour of granular soil materials mixed with granulated rubber: influence of rubber content and mean grain size ratio on shear modulus and damping ratio for a wide strain range

The escalating disposal of end-life tires has led to an urgent need for efficient reuse. The positive environmental impact of the application of this material in large-scale civil engineer construction, such as soil-retaining structures, or as seismic isolation technique, stems not only from the reuse of the tires, but also from the effect this material inherits to the response of these structures. The soil material properties in the form of shear modulus and damping degradation curves, G–γ–D, are key parameters in the numerical analysis of site-specific seismic response and seismic design of structures. To this end, the effect of the dynamic shear strain, γ, on the shear modulus, G, and damping ratio, D, of granular soils mixed with granulated rubber is studied. An experimental approach is presented, employing resonant column and cyclic triaxial tests to obtain an insight on the response of these mixtures in a wide band of dynamic strain. A range of rubber content in the mixture up to 60% per weight is tested, and the influence of the mean grain size ratio of the mixed materials is investigated.

An improved dynamic model for a silicone material beam with large deformation

Dynamic modeling for incompressible hyperelastic materials with large deformation is an important issue in biomimetic applications. The previously proposed lower-order fully parameterized absolute nodal coordinate formulation (ANCF) beam element employs cubic interpolation in the longitudinal direction and linear interpolation in the transverse direction, whereas it cannot accurately describe the large bending deformation. On this account, a novel modeling method for studying the dynamic behavior of nonlinear materials is proposed in this paper. In this formulation, a higher-order beam element characterized by quadratic interpolation in the transverse directions is used in this investigation. Based on the Yeoh model and volumetric energy penalty function, the nonlinear elastic force matrices are derived within the ANCF framework. The feasibility and availability of the Yeoh model are verified through static experiment of nonlinear incompressible materials. Furthermore, dynamic simulation of a silicone cantilever beam under the gravity force is implemented to validate the superiority of the higher-order beam element. The simulation results obtained based on the Yeoh model by employing three different ANCF beam elements are compared with the result achieved from a commercial finite element package as the reference result. It is found that the results acquired utilizing a higher-order beam element are in good agreement with the reference results, while the results obtained using a lower-order beam element are different from the reference results. In addition, the stiffening problem caused by volumetric locking can be resolved effectively by applying a higher-order beam element. It is concluded that the proposed higher-order beam element formulation has satisfying accuracy in simulating dynamic motion process of the silicone beam.