Impact Loading Conditions Research Articles

Plastic dissipation sensitivity to mechanical properties in polycrystalline β-HMX subjected to impact loading

This manuscript investigates the sensitivity of plastic dissipation expressed in the form of temperature rise to anisotropic elasticity constants and crystal plasticity properties of crystalline β-HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) under impact loading conditions. Parametric sensitivity analyses are performed using a global sensitivity analysis framework to quantify the relative roles of the elasticity constants of the monoclinic β-HMX crystal, as well as to delineate thermal activation and phonon drag induced slip mechanisms that contribute to the nonlinear response. The plastic behavior of β-HMX is modeled using a Crystal Plasticity Finite Element model incorporating the slip mechanisms of thermal activation and phonon drag driven by the evolution of dislocation generation and annihilation. The results of the sensitivity analyses show that the anisotropic elasticity coefficients of the monoclinic crystal have a nominal effect on the energy dissipation and temperature rise, dominated by sensitivities of a few coefficients. Among the two primary slip mechanisms, phonon drag appears dominant within the load rate and amplitude regimes considered in this study.

Compression resilience and impact resistance of fiber‐reinforced sandwich composites

This paper presents an experimental investigation on the compression behavior of fiber‐reinforced sandwich composites. In this study, five different types of sandwich composites were prepared with warp knitted spacer fabric as middle layer. Four different types of woven Kevlar fabric structures were used as outer layers (skin) along with one sample of woven basalt fabric. The middle layer used is 100% polyester spacer fabric. Sandwich composites were fabricated using epoxy resin by wet lay‐up method under vacuum bagging technique. Compression behavior, ball burst, and knife penetration were tested for all samples. The effect of outer layer of these composites on the mechanical performance was studied using the compression stress‐strain curves. It is known that spacers have excellent compression elasticity and cushioning. Maximum knife penetration resistance is obtained with twill weave on surface because of maximum yarn cohesion and resin impregnation. Higher amount of cohesive friction results in higher resistance against penetration of sharp objects like the knife edge. Plain and twill fabrics offer sufficient resistance again ball burst. The yarn deformation allows formation of dome shape after ball impact. Maximum impact resistance in ball burst is obtained for plain weave because of highest level of interyarn binding. The results provide new understanding of knitted spacer fabric‐based sandwich composites under compression and impact loading condition.

Modeling and simulation of carbon composite ballistic and blast behavior

The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautical structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic impact and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact and blast loading conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate-dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA® as a user-defined material subroutine. In this paper, the ballistic limit velocity (V50) was first established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. A series of close-in shock hole blast tests on carbon composite panels were then tested and simulated using the LS-DYNA® Arbitrary-Lagrangian-Eulerian (ALE) method integrated with the Army Research Laboratory (ARL) progressive failure composite model. The computational constitutive model has been validated to characterize the progressive failure behavior in carbon laminates subjected to close-in blast loading conditions with reasonable accuracy. The availability of this modeling tool will greatly facilitate the development of carbon composite structures with enhanced ballistic impact and blast survivability.

곡률과 적층배향이 다른 CFRP 적층쉘의 내충격특성

CFRP composite is widely used in various industries because it has excellent mechanical properties under static load conditions. In particular, the CFRP composite is widely used in the aerospace field due to its superior wear resistance and heat resistance. However, under the impact load, temperature and moisture conditions, there is a lot of decrease in strength. In this study, impact experiment were conducted using high-speed impact testing device to examine fracture and dissection of fiber and matrix generated inside the CFRP composite according to the layered composition. In order to establish the conditions of the various specimens, a specimen with the stacking conditions of orthotropic ([0°3/90°3]s) and isotropic ([+45°3/-45°3]s) was constructed. It was found that the orthogonal divergence test specimen was more than twice as likely to increase the critical tube energy than the isotropic test specimen.

Dynamic response and validation of a flexible matrix composite

Testing and predicting the dynamic response of flexible matrix composites in impact loading condition face two primary challenges: (i) experimentally, existing techniques using existing instruments do not always provide high fidelity material data under simultaneous high strain and high strain rate loading conditions; and (ii) finite element simulations of a highly flexible material require many material parameters and complex mathematical formulations. To address these limitations, this research investigation presents a technique originally developed in-house for modeling and validating hyper-viscoelastic materials and applies it toward the flexible matrix composite. Results from a simple low-velocity impact (2 m/s) test on a 75 × 75 mm2 flexible matrix composite indicate that the critical material properties for the low strength, highly deformable matrix in conjunction with an updated constitutive model can accurately predict the dynamic behavior within 10% with respect to the force time history response using MATLAB and ABAQUS/Explicit. Finite element interrogation also shows full field stress response within the composite specimen not easily measured via sensors and deformation matching the behavior observed via high-speed camera. Finally, on-going research in this arena indicates that the technique can be applied to higher rate loading mechanisms, such as a gas gun and Hopkinson bar apparatus, in order to obtain material parameters for even more devastating impact loading strain rates.

Characteristics of breaking coal-rock by submerged jet and its application on enhanced coal bed methane recovery

ABSTRACT Hydraulic slotting is a technique to enhance coal bed methane (CBM) recovery and prevent gas disasters. The drilling fields are usually arranged in floor roadway rather than roof roadway, but submerged jet effects caused by hydraulic slotting in roof roadway have not been carried out extensively. Concerning this issue, this paper conducted a series of numerical simulation and physical experiments on hydraulic slotting in roof roadway. It is shown that when the impact load of middle- and high-pressure water jet is applied to the sample, downlink borehole slotting can cause much stronger disturbance than uplink slotting due to the submerged jet. The fracture characteristics of samples also reflect that cavitation erosion caused by submerged jet promotes the fracture formation under middle and high impact load conditions.

Energy absorption of thin-walled tubes enhanced by lattice structures

Thin-walled structures filled or covered by various materials have been proposed for energy absorption applications in recent years. At this point, additive manufacturing technologies provide an unprecedented opportunity to produce nontraditional low-density filler materials to further improve the energy absorption performance of thin-walled structures. With a similar motivation, novel hybrid structures, in which thin-walled tubes filled with periodic lattice materials, are proposed and the energy absorption behaviors of these structures are investigated under axial impact loading conditions. Two different types of lattice structures (i.e. body-centered cubic structure and body-centered cubic structure with vertical strut) are considered as filler materials, and the effects of number of lattice unit cell, diameter of lattice member and tube thickness on energy absorption characteristics of hybrid structures are examined using validated nonlinear finite element models. The results show that the tube and lattice structures contribute the buckling and bending resistance of each other during progressive deformation of hybrid structures, and a considerable enhancement in energy absorption performance could be achieved with appropriate selection of tube and filler lattice structure parameters. Particularly, the result revealed that the hybrid structures can absorb up to 115% higher impact energy compared with the sum of individual parts of hybrid structures. Besides, the hybrid structures also show promising performance in terms of crashworthiness parameters such as specific energy absorption and crash force efficiency, and thus these structures are recommended as potential candidates for crashworthiness applications.

Application of deep learning neural network to identify collision load conditions based on permanent plastic deformation of shell structures

In this work, we have developed a novel deep learning inverse solution or identification method to determine and identify the impact load conditions of shell structures based on their final state of damage or inelastic deformation. This artificial intelligence approach offers a practical solution to solve the inverse problem of engineering failure analysis based on final material and structure damage state and permanent plastic deformation. More precisely, the machine learning inverse problem solver may provide a practical solution to characterize failure load parameters and conditions based on the final permanent plastic deformation distribution of the shell structure that is under examination. In this work, we have demonstrated that the proposed deep learning method can accurately identify a “practically unique” static loading condition as well as the impact dynamic loading condition for a hemispherical shell structure based the permanent plastic deformation after the impact event as the forensic signatures. The data-driven based method developed in this work may provide a powerful tool for forensically diagnosing, determining, and identifying damage loading conditions for engineering structures in various accidental failure events, such as car crashes, pressure vessel failure, or thin-walled infrastructure structure collapses. The machine learning inverse problem solver developed here in this work may have potential impacts on general forensic material and structure failure analysis based on final permanent plastic deformations.

Evaluation of classic and 3D glass fiber reinforced polymer laminates through circular support drop weight tests

This study presents a new approach method for instrumented drop weight tests, with a central spherical impactor and a circular sample support. The tests were carried out on glass fiber reinforced polymer (GFRP) laminates with three types of reinforcement: plain-woven fabric, stitched plain-woven fabric and 3D non-crimp fabric (NCF). It was found that the plain-woven fabric reinforced laminate showed a more violent destruction mode (a massive fracture crack) in comparison with the other two. The stitched and the 3D NCF reinforced laminates exhibited a better impact resistance manifested by a higher stress at the failure initiation point, and a slower or totally arrested fracture crack growth. The applied methodology proved effective for the evaluation of materials under impact loading conditions. A novel element is the use of fast-frame camera images to measure the displacement of the specimens during the impact. It strongly improved the obtained results and enabled a reliable analysis of the strain-stress progress.

Effect of fiber spacing on dynamic pullout behavior of multiple straight steel fibers in ultra-high-performance concrete

Abstract In this study, the effects of fiber spacing and loading rate on the pullout behaviors of single and multiple straight steel fibers embedded in ultra-high-performance concrete (UHPC) were investigated. Hence, three different fiber spacings, corresponding to the fiber volume fractions of 1, 2, and 7%, and loading rates, i.e., quasi-static and impacts, were considered. Bundled fiber specimens were also fabricated and tested to examine the fiber bundling effect at both the static and impact loading conditions. The test results indicated that the pullout resistance of straight steel fibers in UHPC improved by increasing the loading rate, regardless of their number, spacing, and bundles. Approximately 33–68% greater bond strengths were obtained in the single fiber specimen compared to the multiple fiber specimens at both the static and impact loads. The fiber bundles deteriorated the static pullout resistance, whereas both positive and negative bundling effects were found on the interfacial bond strength and pullout energy, respectively, under the impact loads. The strongest rate sensitivity on the dynamic increase factors of the pullout parameters, such as bond strength, maximum fiber tensile stress, and pullout energy, was found as the fibers were bundled, followed by the single and multiple fiber specimens. For the case of multiple fiber specimens, the loading rate sensitivity increased by decreasing the fiber spacing in general, such that the multiple fibers with closer spacings, corresponding to 2 and 7% by volume, were more sensitive to the rate of loading than their counterparts with greater fiber spacings.

Effect of impact velocity and ligament mechanical properties on lumbar spine injuries in posterior-anterior impact loading conditions: a finite element study.

Traumatic events may lead to lumbar spine injuries ranging from low severity bony fracture to complex fracture dislocation. Injury pathomechanisms as well as the influence of loading rate and ligament mechanical properties were not yet fully elucidated. The objective was to quantify the influence of impact velocity and ligament properties variability on the lumbar spine response in traumatic flexion-shear conditions. An L1-L3 finite element spinal segment was submitted to a posterior-anterior impact at three velocities (2.7, 5, or 10m/s) and for 27 sets of ligament properties. Spinal injury pathomechanism varied according to the impact velocities: initial osseous compression in the anterior column for low and medium velocities versus distraction in the posterior column for high velocity. Impact at 2.7 and 5m/s lead to higher extent of bony injury, i.e., volume of ruptured bone, compared to the impact at 10m/s (1140, 1094, and 718mm3 respectively), lower L2 anterior displacement (2.09, 5.36, and 7.72mm respectively), and lower facet fracture occurrence. Ligament properties had no effect on bony injury initiation but influenced the presence of facet fracture. These results improve the understanding of lumbar injury pathomechanisms and provide additional knowledge of lumbar injury load thresholds that could be used for injury prevention. Graphical abstract Stress distribution analysis at the injury initiation and final injury pattern identification for a lumbar segment submitted to a traumatic posterior-anterior impact.

Plasticity-Damage Modeling of Strain Rate and Temperature Dependence of Aluminum Alloy 7075-T651

This is the first study to correlate the observed damage evolution of ambient (298 K) and elevated (480 K) temperatures of quasi-static and dynamically-loaded wrought aluminum alloy 7075 (AA7075) to capture the strain rate and temperature influence on flow behavior with one set of material constants. In this research, an internal state variable (ISV) framework implementing a physically-based plasticity and damage constitutive model was used to capture the strain rate and temperature dependence of the wrought Al–Zn–Mg–Cu aluminum alloy. The model includes microstructural content processing history and is consistent with continuum level kinematics, kinetics, and thermodynamics. The ISV model captures deformations due to kinematic and isotropic stress-state dependent hardening and damage from the microscale that arise from microstructural features and defects in the wrought aluminum alloy. In addition, the ISV damage theory is based on void nucleation, void growth, and void coalescence. This research provides a foundation for capturing the structure–property relations from the microscale to the structural scale. Finite element methods coupled with internal state variables used to model the plasticity and damage state at the structural scale for high fidelity dynamic loading scenarios, such as blast and impact loading conditions.

Predicting the punching shear failure of concrete slabs under low velocity impact loading

A simplified analytical approach to predict the punching shear failure of a concrete slab under low velocity (<10 m/s) impact loading has been proposed. The proposed analytical approach has further been validated against a backdrop of experimental results available in the public domain. The efficacy of the proposed approach has further been tested against the results obtained by conducting numerical simulations designed by the authors. The results obtained from this simplified approach have on the whole shown good agreement with the experimental results. Furthermore, on the basis of extensive literature review, a state-of-the-art investigation to examine the structural response of concrete slabs under low velocity impact loading has also been presented in this paper. The paper aims to explore and present a quantum of the undertaken research under the sections dealing with the experimental studies, numerical simulations and the analytical modeling. Thus, in addition to the proposition of a simplified approach for predicting the punching shear failure of a concrete slab under low velocity impact loading condition, the paper also sets forth to establish the current knowledge base in this field and identify the key areas with a need for further research with regard to this domain.

Impact Energy Release Characteristics of PTFE/Al/CuO Reactive Materials Measured by a New Energy Release Testing Device.

Metal/polymer reactive materials have been studied and applied in a wide range of ways in recent years. This type of material is insensitive under normal conditions but reacts violently and releases a large amount of chemical energy under high-speed impact or high strain rate loading conditions. Compared with conventional explosives, it has better mechanical properties, and its unit mass energy is several times that of TNT. In this paper, PTFE/Al/CuO reactive materials are the main research objects, and we assess the impact energy release abilities of this type of reactive material through experimental research. To this end, eight sets of material formulations are designed, and the effects of particle size, the ratio of PTFE/Al and Al/CuO materials, and sintering on the energy release ability of the reactive materials are investigated. All experiments are carried out based on a self-designed new energy release testing device. The experimental device can measure the pressure time history curve generated by the reactive materials, and the rationality of the pressure time history curve can also be verified by the displacement time curve of the piston. The results show that with an increase in the Al/CuO thermite content, the energy release rate of the reactive material clearly increases, which is attributed to the reaction threshold of Al/CuO being low and because the heat generated can promote the reaction of PTFE/Al. The energy release rate of the nano-scale reactive materials is higher than that of the micron-scale reactive materials because the reduction in particle size results in a larger specific surface area. Thus, the energy required for ignition is lower. The energy release rate of sintered reactive materials is higher than that of unsintered reactive materials, which can be explained by the interfacial area between Al particles and PTFE particles in sintered reactive materials being larger, which makes the reaction more sufficient. The self-designed energy release testing device for the reactive materials and the conclusions obtained in this paper have clear significance for guiding engineering applications.

Damage and failure mechanism of thin composite laminates under low-velocity impact and compression-after-impact loading conditions

Impact resistance and damage tolerance are of great significance in the design of composite structures. This study investigated the damage and failure mechanism of thin composite laminates under low-velocity impact and compression-after-impact (CAI) loading conditions. Four levels of impact energy were included in the test matrix. Delamination induced by low-velocity impact was captured using ultrasonic C-scan, and a three-dimensional (3D) digital image correlation (DIC) system was employed to measure full-field displacement during the CAI tests. Infrared thermography was also used to online monitor the thermal field variation of the test specimen during the impact and CAI process. The cross sections of typical tested specimens were inspected using an optical microscope and a scanning electron microscope (SEM). A 3D damage model that considers both interlaminar and intralaminar damage was proposed to study the complex damage and failure mechanism. Excellent correlation was obtained between the experimental results and the numerical results. The experimental results obtained from various tests and the results from the numerical simulation were combined to provide a new and deep insight of damage evolution and failure mechanisms under low-velocity impact and CAI loading conditions.

Low-Elevation Impact Tests of Axially Loaded Reinforced Concrete Columns

Conventionally, structures are designed to resist dead and live loads. However, there is a rising risk of structural members being subjected to impact loads as a result of unexpected events, accidents, or intentional attacks. In the case of frontal street-level columns of buildings and columns in parking spaces, they can potentially be exposed to high-intensity dynamic loads caused by vehicular impacts. Furthermore, most of these columns are not designed to resist these effects. This research demonstrates the vulnerability of conventionally designed reinforced concrete (RC) columns against vehicle impacts. A special drop-weight test setup was designed and established to simulate the vehicle collision impact in the performed tests. In the scope of this study, four fullscale axially loaded RC members were tested under drop-weight test setups to represent low-elevation transverse impact loads on the specimens. The performance of RC columns under static and impact loading conditions (applied by increased magnitude of impact energy) was examined and the changes in their structural performances were evaluated. The mode of failure was observed to be transformed from pure flexure in static tests into a more brittle character dominated by shear under impact loading conditions. Consequently, conventionally designed RC columns were found highly shear-deficient against vehicular impacts; therefore, they should be designed with a certain safety margin to have reserve shear and deformation capacities to eliminate their vulnerability. Based on the test results, dynamic response ratio recommended for shear-critical RC members can be used in the design of street-level columns against vehicular impact.

Stress Relaxation of Apples at Different Deformation Velocities and Temperatures

ABSTRACT. Stress relaxation tests on apples (‘Beni Shogun’ variety) were performed at different velocities in the range of 0.0002 to 1 m s-1 and at three temperatures (2°C, 10°C, and 20°C). The generalized Maxwell model was used to describe the experimental stress relaxation curves. The two relaxation times of the model decreased with an increase in the deformation velocity. The relaxation times were related to the processes of gas and liquid flows in the intercellular spaces. This research showed the critical velocity associated with the weakness of the apple structure to lie between deformation velocities of 0.0002 and 0.002 m s-1, where a rapid decrease in the two relaxation times occurred. An increase in the peak force response with increasing deformation velocity showed the viscoelastic behavior of apple flesh. The equilibrium modulus describing the material condition after deformation was much larger under the quasi-static loading condition than the impact loading condition at all deformation velocities. The temperature did not seem to affect the Maxwell model parameters and peak force response for all deformation velocities under both loading conditions. Keywords: Apple, Generalized Maxwell model, Impact loading, Quasi-static loading, Stress relaxation, Viscoelasticity.

Crashworthiness performance of stiffened bottom tank structure subjected to impact loading conditions: Ship-rock interaction

Abstract Shipping time, cargo handling and quality as well as operational cost are main aspects of success in trading and shipping, which leads to high demand for ship safety. During freight shipping is conducted for various cargoes, the ship structure is subjected to numbers of loads, which several of them have been predicted during ship design. Nevertheless, incidental type in form of impact load can deliver massive blow to ship safety and cause immense loss. This phenomenon may be worse than initial condition if structure of chemical-oil carrier experiences impact, which possibly evokes environmental damage to maritime territory. This work is addressed to assess crashworthiness performance of structural part, i.e. bottom tank of chemical carrier. This part is one of center point of oil spill during occurrence of the impact load. The loading conditions are defined as configuration of interaction between ship structure and rock when the ship is stranded on shallow water. A series of data observations produced by finite element analysis (FEA) provide a prediction regarding local member’s motions during the rock breaches lower parts of the bottom tank. Consequences of the plate towards failure are quantified to obtain effect of the selected impact loading conditions to directly involved (main) member and other affected local member.

Comparative pullout behavior of half-hooked and commercial steel fibers embedded in UHPC under static and impact loads

This study investigates the pullout behaviors of various steel fibers embedded in ultra-high-performance concrete (UHPC) under static and impact loading conditions. For this purpose, four types of steel fibers, i.e., straight, hooked, twisted, and half-hooked, and three different loading rates applied by static and impact pullout test machines were adopted. To examine the effect of inclination angle on the pullout behavior, four different inclination angles of 0°, 30°, 45°, and 60° were considered. Test results indicate that the highest average bond strengths were found for the hooked and twisted fibers for static and impact loads, respectively, whereas the straight fibers exhibited the lowest bond strength at all inclination angles. The effectiveness of using half-hooked fibers increased when they were inclined, and maximized at an inclination angle of 45° compared to straight and highly deformed fibers. The use of the twisted and half-hooked fibers was also more effective in static pullout energies than the hooked and straight fibers. The pullout resistance of all the steel fibers in UHPC was improved under impact loading conditions, and the order of the loading rate effectiveness regarding both the average bond strength and pullout energy was as follows: straight fibers > half-hooked fibers > twisted fibers > hooked fibers. The change in the failure mode from pullout to rupture, due to the increase in the loading rate, adversely affected the rate sensitivity of the bond strength and energy absorption capacity. Since the deformed steel fibers were easily ruptured under impact loads, their rupture failure needs to be prevented to achieve an excellent bond strength and energy absorption capacity.

A Deep Learning-Based Computational Algorithm for Identifying Damage Load Condition: An Artificial Intelligence Inverse Problem Solution for Failure Analysis

In this work, we have developed a novel machine (deep) learning computational framework to determine and identify damage loading parameters (conditions) for structures and materials based on the permanent or residual plastic deformation distribution or damage state of the structure. We have shown that the developed machine learning algorithm can accurately and (practically) uniquely identify both prior static as well as impact loading conditions in an inverse manner, based on the residual plastic strain and plastic deformation as forensic signatures. The paper presents the detailed machine learning algorithm, data acquisition and learning processes, and validation/verification examples. This development may have significant impact on forensic material analysis and structure failure analysis, and it provides a powerful tool for material and structure forensic diagnosis, determination, and identification of damage loading conditions in accidental failure events, such as car crashes and infrastructure or building structure collapses.