Stress Wave Propagation Research Articles

Hybrid ratio optimizations on ballistic penetration of carbon Kevlar UHMWPE fiber laminates

Fiber hybrid is a promising strategy for improving ballistic penetration behaviors of fiber-reinforced laminated composites. Ballistic impact performance of hybrid fiber laminates against projectiles depends on various parameters not only with respect to the material properties, fiber types, yarn properties, fabric structures of the constituent plies but also with the hybrid configuration, material combinations and stacking sequences. It has a substantial growth demand to obtains the optimal hybrid design of the fiber hybrid composites, for maximizing the potential of the constituent materials and improving the overall anti-impact performance of the hybrid composites. However, the effect of the hybridization ratios on ballistic penetration behaviors of the hybrid composites is still infant. Here we report the hybridization ratios on ballistic impact damage of carbon/Kevlar/UHMWPE (ultra-high molecular weight polyethylene) hybrid laminates through ballistic impact experiments and three-point bending tests. The fiber hybrid laminates with different hybrid ratios had been fabricated and studied under the impact of FSP (fragment simulating projectiles). The effect of the hybridization ratios on the flexural behaviors, ballistic curves, energy absorptions and damage modes were investigated. The FEA (finite element analysis) was carried out from meso- to macro- scale model. We found that the flexural behaviors are related to the material properties and mechanical balance among different material components in the hybrid systems. The damage modes for various hybrid ratios have a typical impact damage mode like matrix cracking, fiber breakage and delamination. A rational accuracy in residual velocities and damage modes can be obtained between ballistic experiments and FEA results. The hybrid ratios would affect the stress wave propagation in the composites with a gradual attenuation development and lead to different failure mechanisms. This study is expected to reveal a fundamental failure mechanism for the fiber hybrid composites incorporated with three different fiber combinations in different hybrid ratios under ballistic impact. The results can provide important theoretical basis and experimental reference for designing and developing hard multiphase anti-impact composite structures.

Detection of “zero-volume” defects in concrete repair systems using impact-echo method

Adhesion in this system is one of the most important factors that affect the reliability and durability of repair. According to the many standards and guidelines, a pull-off test is recommended for assessment of a bond quality in repair systems. However, a growing interest in development of non-destructive techniques (NDT) for evaluation of concrete structures is recently noted. A majority of NDT methods mentioned in EN 1504-10 for repair efficiency assessment are based on propagation of stress waves. The impact echo method is considered as a one of the promising. The literature data confirmed that the “non-zero volume” defects containing air are relatively easy to detect with impact-echo method if they are large enough. It is more complex to detect “zero-volume” defects, e.g dust or any other antiadhesion material. In this work usability of impact-echo for detection of “zero-volume” defects in repair systems is discussed.

Experimental and mesoscale analysis on wave propagation induced by impact in dry silica sand

When investigating the propagation of stress waves in sand-like materials, the materials are generally modeled as homogeneous parts despite their complex structures comprising numerous particles of varying sizes and shapes. However, this approach fails to consider the non-continuum nature of sand-like materials. To address this issue, a mesoscale numerical model of silica sand particles with random shapes and three sizes is employed in this study to numerically analyze wave propagation. Experimental data from an upgraded split Hopkinson pressure bar test are utilized to validate the accuracy of the numerical model. Using the validated numerical model, we investigate the impact of relative densities, incident wavelengths, and wave amplitudes on stress wave attenuation in dry silica sand. Empirical equations are derived from summarizing the stress wave attenuation law induced by impact loading. The study shows that relative density and wavelength are critical factors affecting the residual peak stress ratio in silica sand, while the effect of loading wave amplitude is limited.

Detection of Gas Pipeline Leakage Using Distributed Optical Fiber Sensors: Multi-Physics Analysis of Leakage-Fiber Coupling Mechanism in Soil Environment

Optical fiber sensors are newly established gas pipeline leakage monitoring technologies with advantages, including high detection sensitivity to weak leaks and suitability for harsh environments. This work presents a systematic numerical study on the multi-physics propagation and coupling process of the leakage-included stress wave to the fiber under test (FUT) through the soil layer. The results indicate that the transmitted pressure amplitude (hence the axial stress acted on FUT) and the frequency response of the transient strain signal strongly depends on the types of soil. Furthermore, it is found that soil with a higher viscous resistance is more favorable to the propagation of spherical stress waves, allowing FUT to be installed at a longer distance from the pipeline, given the sensor detection limit. By setting the detection limit of the distributed acoustic sensor to 1 nε, the feasible range between FUT and the pipeline for clay, loamy soil and silty sand is numerically determined. The gas-leakage-included temperature variation by the Joule-Thomson effect is also analyzed. Results provide a quantitative criterion on the installation condition of distributed fiber sensors buried in soil for the great-demanding gas pipeline leakage monitoring applications.

Multi-stage finite element modeling of the deformation behavior during ultrasonic-assisted incremental sheet forming

The incremental sheet forming (ISF) has the characteristics of high flexibility, short lead time and enhanced formability. However, it still needs to be further improved in the aspect of forming quality (e.g. geometric accuracy and surface finish). The introduction of ultrasonic energy field may improve the deformability of sheets and the performance of parts, and reduce the load during sheet metal forming. The present work aims to meticulously investigate the influence of ultrasonic vibration on the deformation mechanism of material in several periods. First, based on an improved material constitutive model which considers both the thermal activation and dislocation density evolution process, a multi-stage finite element model of UISF was established. In particular, the multi-stage finite element model of UISF is divided into two stages, the full contour forming stage and the local forming stage, in which a transient simulation with high frequency output was realized. The influence of vibration parameters on the forming force as well as the distribution of stress and strain field in the forming process was comprehensively analyzed. The results show that the ultrasonic vibration reduces the forming force obviously (53% at amplitude of 10 µm), which is due to the dynamic impact effect and acoustic softening effect. Four distinct stages, approaching, loading, unloading and departing, are observed in a single vibration period. The dynamic impact effect of ultrasonic vibration changes the contact state between sheet and forming tool and causes the continuous propagation of dynamic oscillatory stress wave inside the material (propagate to the entire plate at 0.002 s), which leads to the significant change of stress and strain field. At the same time, the maximum stress is significantly reduced (73% at amplitude of 10 µm). By applying ultrasonic vibration on the stress-strain field, it is found that these vibrations mainly act on the contact region between the sheet and forming tool. The high frequency vibration makes smooth stress distribution along the path as well as spread over the whole sheet area to create a uniform distribution. Benefitting from the smooth stress distribution, the vibration also promotes greater formability with good forming quality and the plastic deformation mainly occurs in the side wall deformed area. The present work provides a practical simulation approach to study the transient deformation behavior of materials under the ultrasonic field.

Experimental study on dynamic compression behavior characteristics and stress wave propagation law of rigid-flexible combinations under cyclic bi-directional impact loading

To explore the dynamic compression behavior and damage evolution characteristics of “rigid-flexible coupling” surrounding rock supporting structure. Split Hopkinson pressure bar (SHPB) was used to carry out constant amplitude cyclic bi-directional impact compression tests on the combination specimens of “rigid-rigid: rock (sandstone)-like material (RLM) - normal cement mortar (NCM)", “rigid-flexible: RLM - rubber cement mortar (RCM)" and “flexible-rigid: RCM - high-performance supporting concrete (HPSC)". The characteristics of stress-strain curve evolution, stress attenuation, strain growth, energy transformation, damage evolution characteristics, and damage state were compared and analyzed. The results show that compared with RLM-NCM, RLM-RCM and RCM-HPSC had remarkable dynamic yield ductility and excellent impact resistance. RCM and HPSC can work together to hinder the dynamic damage development of “rigid-flexible coupling” supporting structure and surrounding rock. Based on the one-dimensional stress wave propagation theory, the stress wave propagation models of rigid-flexible combination specimens under SHPB cyclic bi-directional impact were established, and the corresponding stress wave propagation equations were derived, which profoundly revealed the propagation law and attenuation mechanism of stress waves in SHPB impact rigid-flexible combination tests. Finally, based on the energy drive theory and residual energy theory, the impact instability energy criteria of surrounding rock under the rigid component combined support system and “rigid-flexible coupling” component combined support system were analyzed and discussed.

Research on plastic structural wave behavior and crashworthiness of continuous gradient mesoscopic foam structures under high speed impact

Under high speed impact, the macro and mesoscopic mechanical behavior, the stress wave propagation mechanism, and the relationship between density gradient and crashworthiness of continuous density gradient foam are the key issues to improve and optimize the protection capability of support structures. The numerical simulation of various density gradient foams is carried out, and the meso-discontinuity of foams is overcome by using the local gradient tensor method of least square error, and the plastic structure wavefronts with clear interfaces are obtained. The plastic structure wave propagation mechanism of foam with different density configurations was analyzed and the relationship between density gradient and crashworthiness was further revealed. The results show that inertia effect is the dominant factor of collapse in the early stage of impact. In the middle and late stage of impact, the dominant factor of collapse changes to the microscopic density of foam. The distribution of continuous density gradient significantly affects the impact resistance. Compared with low-high density configuration foam (LH), high-low density configuration gradient foam (HL) has a 140% increase in impact end force, a 24% decrease in support end force, a 3% decrease in maximum compression, and a 41% longer response time.

Research on the influence of stress wave on crack and chip formation mechanism in radial ultrasonic vibration assisted grinding

The propagation of stress waves in the ultrasonic vibration grinding zone was studied and analyzed in this paper and the microscopic mechanism of ultrasonic vibration assisted grinding is clarified by combining the method of finite element analysis (FEA). The creation of an experimental platform for ultrasonic vibration assisted grinding allowed for a comparative experimental evaluation of radial ultrasonic vibration assisted grinding (RUVAG) and conventional grinding (CG). Experiments analysis show that: (a) Compared with conventional grinding, the alternating impact of stress waves in ultrasonic vibration grinding is beneficial to the propagation of microcracks and the removal of materials. Meanwhile, there is no burn on the machined surface, so the quality of the machined surface is better. (b) Under the alternating and superimposed action of stress waves, dislocation emission becomes difficult due to the suppressed thermal activation process. Therefore, the plastic deformation of the material is suppressed and reduced in the grinding zone, and the material is more likely to break than during conventional grinding. Therefore, compared with conventional grinding, both cracks and chips are easier to form in it..

Study of presplit blasting under high in-situ stress

High in-situ stress generally results in difficulties in achieving crack interconnection in presplit blasting, which can further arouse challenges related to construction cost and schedule of rock engineering. In this study, the crack interpenetration in presplitting under high in-situ stresses is theoretically analysed according to the propagation and superposition of stress waves, and then the relationships between in-situ stress, hole spacing and charge diameter in presplitting are analytically established. Following, based on the theoretical results, the rock cracking and crack coalescence induced by presplitting under different in-situ stresses are numerically investigated with a two-hole planar model in LS-DYNA. The simulation results demonstrated the effectiveness of presplitting. Subsequently, to provide guidance for practical application, presplitting with multi-holes in circular tunnel excavation under high hydrostatic pressure and high anisotropic in-situ stress is numerically performed. The performances of presplitting under high in-situ stress using different methods such as changing hole spacing and adjusting charge diameter are analysed and compared. Based on the theoretical analysis and numerical findings, we suggest that drilling boreholes along the direction of the major principal stress, using less charge, and employing small and uniform hole spacing can be effective in presplitting under high in-situ stress. This study provides insights into the mechanisms of crack interpretation in presplitting and offers guidance for overcoming difficulties in controlled blasting under high in-situ stress.

Energy-conserving interface dynamics with asynchronous direct time integration employing arbitrary time steps

The derivation and implementation of an asynchronous direct time integration scheme for domain-decomposed finite element models is presented. To maximize clarity in the description of the proposed asynchronous integration, the scheme is restricted to the linear-elastic stress wave propagation case. The proposed method allows the integration of individual subdomains with independent time steps. There is no requirement for an integer time steps ratio of the interacting domains while maintaining zero interface energy. The subdomains are connected by the condition of the continuity of the acceleration field at the interface. In addition, the a posteriori technique is applied to satisfy the continuity of the displacement and velocity fields. Another important contribution of this paper lies in the description of the implementation — we offer the reader a general description of the implementation of the case of any number of subdomains with any number of constraints between them, while the basics of the algorithm are explained on a single domain pair. The functionality of the asynchronous integrator is verified by solving selected problems and comparing with analytical solutions and experimental measurements obtained using a Split Hopkinson pressure bar setup.

FEM-SPH Coupling Approach for Impact Response Analysis of Composite Plates with Brick-and-Mortar Structure

Bioinspired nacre-like composites have attracted increasing research interests recently. They are typical composites with brick-and-mortar structure and usually employ a combination of hard material and soft material to achieve a good balance between stiffness and toughness. Impact response analysis of such composites is difficult due to their complex structure and interface. In this work, an effective finite element method-smoothed particle hydrodynamics (FEM-SPH) coupling approach is developed for impact response analysis of composite plates with brick-and-mortar structure. In the approach, hard material taking up the bulk of the composite plate is modeled with the SPH method, and soft material forming thin layer structures in the composite plate is modeled with FEM. A coupling algorithm considering failure behavior is proposed to model bonding interfaces between FEM parts and SPH parts. A particle-to-particle SPH contact algorithm is employed to handle contacts between SPH parts, and a penalty-based FEM-SPH contact algorithm is implemented to treat contacts between FEM parts and SPH parts. The developed coupling approach is used to calculate stress wave propagation in two bonded plates of the same material and different materials and a composite plate with brick-and-mortar structure. The accuracy of the coupling approach is validated by comparing the calculated results with those of analytical method and FEM. The coupling approach is then used to simulate the effects of some factors on the impact damage of composite plates with brick-and-mortar structure. The coupling approach can conveniently model the complex structure and bonding interface of the composite plates and is capable of capturing interface failure and fragmentation of the major composition of the composite plates during impact events. It provides a promising alternative for the impact response analysis of brick-and-mortar composite structures.

Study of stress wave propagation across a non-persistent joint based on a boundary integral equation method

Studies on stress wave propagation across persistent joints have been conducted extensively. Nevertheless, there exists a consensus that non-persistent joints are widely and densely distributed, which have a profound impact on wave propagation in jointed rock masses. A boundary integral equation method is suggested in this paper to investigate the characteristics of transmitted wave field for the case of stress wave propagation across a single non-persistent joint. The displacement continuity and discontinuity boundaries are combined in the method. The method presented in the current study is applicable to the analysis of wave propagation across non-persistent joints with arbitrary incident angles. Then, taking a single non-persistent joint arranged with only one joint segment as an example, the applicability of the method in dealing with the problems of wave propagation is verified by comparing the results with those from the discrete element method and analytical methods. Subsequently, parametric studies are carried out, including the effects of joint-segment length, rock-bridge length, wave frequency and incident angle on the transmitted wave. The result indicates that the existence of non-persistent joint makes the transmitted displacement field different from that of persistent joint, because the scattered wave is produced during the process of wave propagation. The displacement amplitude may be amplified evidently in some regions and the spatial distribution pattern of the transmission coefficient is closely related to the joint-segment length, rock-bridge length and incident wavelength.

The Influence of the Strain Rate and Prestatic Stress on the Dynamic Mechanical Properties of Sandstone-A Case Study from China.

A series of conventional dynamic uniaxial compressive (CDUC) tests and coupled static dynamic loading (CSDL) tests were performed using a split Hopkinson compression bar (SHPB) system to explore the variable dynamic mechanical behavior and fracture characteristics of medium siltstone at a microscopic scale in the laboratory. In the CDUC tests, the dynamic uniaxial strength of the medium sandstone is rate-dependent in the range of 17.5 to 96.8 s-1, while the dynamic elastic modulus is not dependent on the strain rate. Then, this paper proposes a generalized model to characterize the rate-dependent strength from 17.5 to 96.8 s-1. In the CSDL tests, with increasing initial prestatic stress, the dynamic elastic modulus and dynamic strength increase nonlinearly at first and then decrease. The results show that two classical morphological types (i.e., Type I and Type II) are observed in the dynamic stress-strain response from the CDUC and CSDL tests. By scanning electron microscopy (SEM), microscopic differences in the post-loading microcrack characteristics in the behavior of Type I and Type II are identified. In Class I behavior, intergranular fracture (IF) usually initiates at or near the grains, with most cracks deflected along the grain boundaries, resulting in a sharp angular edge, and then coalesces to the main fracture surface that splits the specimen along the direction of stress wave propagation. In contrast, Class II behavior results from the combined IF and transgranular fracture (TF).

Formulation for wave propagation in dissipative media and its application to absorbing layers in elastoplastic analysis using mathematical programming

AbstractIn this article, we propose a new solution scheme for modeling elastoplastic problems with stress wave propagation in dissipative media. The scheme is founded on a generalized Hellinger–Reissner (HR) variational principle. The principle renders the discretized boundary‐value problem into an equivalent second‐order cone programming (SOCP) problem that can be resolved in mathematical programming using the advanced optimization algorithm—the interior point method. In such a way, the developed method not only inherits admirable features of the SOCP‐based finite element method in solving elastoplastic problems but also enables the enforcement of absorbing layers (i.e., Caughey absorbing layer), which is essential in modeling stress wave propagation problems, to absorb wave energy. The proposed scheme is validated via the comparison between analytical and numerical results for seismic wave propagation in dissipative media. Its application to elastoplastic dynamic problems with stress wave propagation is also illustrated to demonstrate its efficiency.

An analytical approach of design for recycling of laminate structures by the use of magnetic pulse disassembling

Composite materials in association with metal sheets or ceramic coatings have found a variety of applications, especially as load-bearing components in composite structures. Their disassembly for recycling or maintenance has therefore become more complex. The magnetic pulse technique, usually dedicated to dynamic forming and welding processes, can be used to separate composite materials of a laminate structure of their recyclable adjacent materials. This technology profits from Lorentz forces appearing in electrically conductive materials placed in the vicinity of conductors in which high-intensity electrical discharges are performed. These body forces act locally during the fast energy discharge, from which a stress wave propagates in the structure. The propagation of this stress wave can be used to generate interfacial tensile stress in laminate structures or assemblies. Especially, this technique can be used for evaluating the dynamic bond strength of an interface. This works aims at determining the required conditions for disassembling a laminate structure using a magnetic pulse imposed on one side of the assembly, without significantly damaging the debonded layers. Ideally, the generated interfacial tensile stress should be greater than the interfacial bond strength. In this paper, a one-dimensional analytical analysis is performed in linear elastodynamics on a tri-layered laminate structure, infinite in transverse directions, based on the method of characteristics. An optimisation problem is defined, maximising the interfacial stress between the first two layers, whose solution requires to study various configurations of the assembly involving different sets of characteristics in the laminate, associated with different areas of the domain of feasibility spanned by the unknown vector. Some assumptions and introduced simplifications of the optimisation problem allows to follow a simple two-stage solution procedure, first with respect to the thickness of the first layer for a given stress pulse, then with respect to material impedances of all layers. Several configurations of the assembly are shown to create a sufficiently large interfacial tensile stress to reach the crack initiation and propagation, and a maximum tensile interface stress of twice the maximum applied pressure is obtained in the asymptotic limit.

Dynamic responses and damage behavior of hollow RC piers against rockfall impact

Rockfall impact on bridge piers poses a challenge to the safety of bridge structures in mountainous regions. Hollow reinforced concrete (RC) piers are one of the popular constructional elements in engineering construction, and their impact behavior has not been fully investigated. Therefore, this study aims to explore the dynamic responses and damage behavior of hollow RC piers under rockfall impact. A finite element (FE) model of a hollow RC pier is established and validated against experimental tests. The validated model is then utilized to investigate the impact force, lateral displacement, internal forces, and failure mode of the hollow pier under rockfall impact. A parametric study is conducted to examine the effectiveness of rockfall diameter, impact velocity, axial force, impact elevation, and reinforcement ratio on the dynamic responses and damage modes of hollow piers. The results show that hollow piers under rockfall impact are prone to suffer serious localized damage with concrete spalling at the front panel, which plays a significant role in the pier’s global response. The stress distribution of cross-sections near the impact position is governed by the stress wave propagation and sectional internal force. Increasing the rockfall diameter would change the resistance mechanism of the front panel and enlarge the peak impact force (PIF) due to the influences of side panels and impact energy. The effects of impact elevation, axial force ratio, and reinforcement ratio are marginal on the impact force but significant on the lateral displacement and damage of hollow piers. This study provides a comprehensive understanding of impact performance of hollow RC piers and offers useful insights for their design and protection against rockfall hazards.

A Novel Damage Assessment Method for RC Beam Using Force-Hammer Excitation and Piezoelectric Sensing Technology

Concrete is the most commonly used construction material in infrastructural projects, but it may suffer from damages because of the heavy loads, fatigue, and harsh service environments. Therefore, it is crucial to detect damage for evaluating the structural conditions and providing guidance for daily maintenance and timely alarm. This paper presents a novel method for damage assessment that offers an easy-carried detection process with a large monitoring range. The proposed method involves exciting stress waves using a force-hammer and receiving them with piezoceramics pasted on the structure. The structural conditions are then evaluated using the Pearson correlation coefficient (PCC) of stress waves received from different stages. To verify the feasibility of the proposed method, a numerical model is innovatively established to study the stress wave propagation in a reinforced concrete (RC) beam with actual damage induced by the external load based on the concrete damaged plasticity (CDP) model. The experimental study is then conducted to demonstrate the effectiveness of the method and the accuracy of the numerical simulation. The numerical and experimental results show a good correlation, illustrating that the proposed method can not only effectively distinguish whether damage occurs but also determine the structural condition from the elastic phase to failure. The proposed monitoring method in this study has great potential for fast damage assessment of RC structures for both lab research and practical applications.

Experimental characterization of cyclic behaviour of pure lead: Temperature sensitivity and strain-rate effects

Proton beam pulses with an energy of 20 GeV/c collide with a pure-lead based target installed in the neutron Time-Of-Flight facility (n_TOF) at the European Laboratory for Particle Physics (CERN). The interaction between the proton beam and lead produces neutrons via spallation mechanism and results in a rapid temperature increase and propagation of stress waves. To evaluate the material response in such challenging conditions, a reliable thermo-mechanical characterization is necessary for the calibration of an appropriate constitutive model for pure lead that is valid under cyclic plasticity and high temperature. In this work, the experimental bases for the development of such constitutive material description are lied. Starting with metallurgical characterization, the typical grain size of the material was initially investigated as well as any variations in the metallurgical features. The grains appeared to have an equivalent size ranging from 2 to 6 mm. Then, static tensile tests were conducted at room temperature and different strain-rates from 10−1 to 10−4 s−1. The obtained results were crucial for optimizing the specimen geometry and test setup for the subsequent cyclic tests. Tension-compression cyclic tests were performed at different strain amplitudes from 0.1 to 1.5%, and at three different temperatures (room temperature, 90 °C and 150 °C). The strain amplitudes were controlled by an extensometer and the strain field evolution during the test was recorded by means of 2D DIC.

Research on Laplace transform of stress wave propagation relaxation function in multi-layer media

There are some difficulties in solving the theory of stress wave propagation in multi-layer media. To solve the problem of stress wave propagation in multi-layer media under the impact load, this paper theoretically makes further derivation and discussion based on viscoelastic analogy method. To further verify the feasibility of the theoretical solution, LS-DYNA is used to simulate the three-layer medium. The simulation results show that comparing the peak stress obtained from the numerical inversion of the Laplace function after the Laplace transform with the simulation results, the maximum error of the peak stress is about 9.5%, and the minimum error is about 1.7%. The results show that the theoretical solution agree with the simulation results, and the theoretical solution has specific feasibility. The theoretical solution method deduced in this paper further develops the viscoelastic analogy method, which has a specific reference value for the rapid calculation of the stress wave propagation law in multi-layer media.

Stress waves in laser-material interaction: From atomistic understanding to nanoscale characterization

During pulsed laser-assisted manufacturing, the extremely high-temperature gradient in space will lead to very high-stress waves that play a critical role in structuring. Both shear and normal stress waves emerge in space. This work provides a review and perspective based on our past work spanning theoretical analysis, 1D molecular dynamics (MD) modeling, 3D MD modeling, and experimental characterization. Discussions are given on the non-Fourier effect during ultrafast laser-material interaction, stress-induced structural defects in recrystallization, and ablation confinement by ambient gas and nanotip during nanotip-assisted near-field nanomanufacturing. The presence of stress waves in space could cause permanent and temporary damages, and these damages are more caused by the shear stresses than the normal ones where the compressive component usually is much stronger than the tensile part. Due to the fact of very fast stress waves propagation and slow cooling and solidification, it is very challenging to conduct MD modeling of the entire domain even using stage-of-the-art parallel computation. Hybrid modeling that combines MD and macroscale modelings provides a better choice to tackle this problem. Time-resolved ultrafast temperature and stress characterization are still highly needed to provide deep physics understanding of laser-material interaction toward process control and optimization.