Rarefaction Wave Propagation in Origami-Based Mechanical Metamaterials

We design origami-based mechanical metamaterials composed of Tachi-Miura Polyhedron (TMP) cells, and we numerically study the propagation of nonlinear waves in them. In order to investigate the dynamics of origami structures, we model these TMP-based metamaterials into a simple multi-bar linkage model. By using this model, we find that these TMP cells exhibit strain softening behavior under compression, which can be tuned by modifying their geometrical configurations or initial conditions. By leveraging such tunable strain softening mechanisms, we verify that the origami-based metamaterials can support the propagation of rarefaction waves. These waves feature tensile wave-fronts despite the application of compressive impact to the system. Such unusual characteristics can be exploited to disintegrate shock waves in a controllable and efficient manner, thereby leading to potential applications in impact mitigation and absorption.

The Investigation of Dynamic Stress Equilibrium of Compact Tension Specimen Based on Hopkinson Tension Bar Device

This article study the dynamic fracture behavior of compact tension specimens under tensile wave loading[1-3]. And the test - numerical hybrid method is used to satisfy the condition of dynamic stress equilibrium. The initial load for numerical simulation is based on the experimental data. In that case, the numerical simulation results can be used to analysis the dynamic stress equilibrium.

A Further Study on the Mechanism of Pre-Splitting in Mining Engineering

In this paper, the mechanism of pre-splitting was analysed using both theoretical and numerical methods. An analytical approach was derived based on the thick-wall cylinder theory. Numerical simulation of pre-split blasting of a two adjacent blast-hole bench was conducted using FLAC3Dsoftware. The sequential loading stages of explosive and stress wave were simplified to a triangular shape pulse and applied to the inner wall of blast-holes. Blast wave fronts and plastic zones were monitored in different elapsed times after detonation. Numerical findings show that collision between the two adjacent stress waves induces a tensile wave, playing the key role in pre-splitting.

Experimental Investigation into Spall of Carbon Phenolic Composites

The velocity history of free-surface particle for carbon phenolic composites (density is 1.4g/cm3) is obtained based on the loading technology of the light gas gun, the relationship between the striking velocity of flyer and the spall thickness as well as time is investigated. Besides, spall strength and thickness are obtained by analyzing the samples data and curves. The high pressure physical characteristics, such as type Hugoniot curve and Murnagham state equation for this material, are acquired by analyzing the velocity history of free-surface and spall characteristics. This study provides a methodology to quantify spall and physical characteristics for carbon phenolic composites under tensile wave loading.

Design Issues of a Kolsky Tension Bar

In general, materials exhibit an increase of strength when loaded at high strain rates, which should be taken into account when dealing with structural impact. Kolsky developed an equipment operating based on elastic wave propagation capable of submitting a material sample to high strain rates. This paper presents some design features of such a tensile wave machine, including mechanical and electronic design issues, which may be helpful in a design phase.

Mathematical theory and analytical solutions for the wave catching-up phenomena in a nonlinearly elastic composite bar

Cracking induced by tensile wave at the free surface of an impacted target is an important issue in impact-resistant design. Here, we explore the use of material nonlinearity to undermine the strength of the tensile wave. More specifically, we consider waves in a two-material composite bar subjected to impact loading at one end. Multiple reflections cause a tensile wave being transmitted into the second material. The attention is on analytically and numerically studying the phenomenon that the tensile wave catches the first transmitted compressive wave. It turns out that, depending on the interval of the initial impact, catching-up phenomena can happen in two wave patterns. A general mathematical theory is provided to show the existence of these patterns together with some qualitative information. To gain more insights into such phenomena, asymptotic solutions are also constructed, which provide both qualitative and quantitative results on the requirement of the constitutive relation, the time and place at which the catching takes place, and how the initial impact, material and geometric parameters influence the solutions. Numerical simulations are also performed, confirming the validity of the analytical results. The analysis and results presented here could be useful for designing a composite structure that has a good impact-protection performance.

Energy Dissipation in Explosive Welding of Dissimilar Metals

Explosive welding of two dissimilar metallic sheets is accomplished by the exhaustive deformation owing to high pressure and high temperature created at the collision place. This study addresses the analytical estimation of the dissipation of potential energy of the explosive initially to mechanical energy and then to thermal energy in dissimilar Copper – Low carbon steel combination. The emanating pressure in the region of detonation front is transmitted to flyer surface as compressive stress wave and a reflective tensile wave is generated at the bottom surface of the flyer. A dilational wave and shear wave are generated. As the flyer plate moving with the transmitted wave collides with the parent, the available kinetic energy is converted into thermal energy to produce adequate heat to induce plastic deformation thus resulting into a strong metallurgical bond.

Impacts on thin elastic sheets

We study transverse impacts of rigid objects on a free elastic membrane, using thin circular sheets of natural rubber as experimental models. After impact, two distinct axisymmetric waves propagate in and on the sheet. First, a tensile wave travels at sound speed leaving behind the wavefront a stretched domain and then a transverse wave propagates on the stretched area at a lower speed. In the stretched area, geometrical confinement induces compressive circumferential stresses leading to a buckling instability, giving rise to radial wrinkles. We report on a set of experiments and theoretical remarks on the conditions of occurrence of these wrinkles, their dynamics and wavelength.

Use of Shock Waves to Measure Adhesion at Interfaces

ABSTRACTThe central problem in the study of composite materials is the adhesive strength of the electronic bond between reinforcement and matrix. We have introduced a unique method of measuring the interface bond strength of a wide variety of engineering interfaces (e.g. metal/ceramic, semiconductor/metal, metal/polymer). Specimens are composed of a relatively thin overlayer on a thick substrate. The specimens are shocked using a magnetic hammer which accelerates a thin metal flyer onto the substrate. The shock, upon reflection at the free surface, is incident on the bonded interface as a tensile wave, spalling the overlayer. The method is unique in using free surface velocity measurements to determine the interface stress at the instant of separation. The debonding process is sufficiently rapid (on the order of 1.0 ns) that debonding occurs by the simultaneous breaking of atomic bonds, rather than by propagation of cracks nucleating at stress concentrations near existing flaws.