Quasi-static Compressive Stress Research Articles

Compressive performance of paper honeycomb core layer with double-hole in cell walls

The perforated paper honeycomb structure with double-hole in cell walls is one kind of innovative sandwich structure also to improve drying process of traditional honeycomb paperboard. Based on the analytical calculation, experiment inspection and finite element analysis, this paper is focus on the paper honeycomb core layer with double-hole in cell walls, and especially studies the bending and folding deformation and the compressive strength under out-of-plane quasi-static compression for different humidity. The structure first appears elastic buckling and folds near the circular holes in the cell wall, and goes on buckling, folding and crushing until to the densification with the continuously increase of compression set. Its quasi-static compressive stress and strain curve mainly shows four kinds of compression deformation processes, such as linear elastic stage, elastic yielding stage, plastic collapse stage, and densification stage. The critical stress and plateau stress of the structure slowly decrease with the increase of humidity and aperture, and the multiple linear regression analysis result illustrates that the relative humidity has much more influence on the critical stress and plateau stress. For different humidity and aperture, the analytical calculation result is close to the experiment result. However, the finite element simulation result greatly deviates from the above two results, especially for relative humidity 50% and 60% cases.

DISLOCATION-BASED CONSTITUTIVE DESCRIPTION FOR MODELING OF THE 6008 ALUMINUM ALLOY BEHAVIOR

The behavior of the 6008 aluminum alloy under impact loading with different strain rates is experimentally studied. Quasi-static compressive stress–strain curves of these materials are obtained in this study by using an RPL100 material testing machine and a split Hopkinson pressure bar. As the strain rate increases, the yield stress and the peak stress of the materials are found to increase significantly. The adiabatic temperature rise generated during the impact process makes the materials soften, so that the rate of the increase in the flow stress gradually decreases with an increase in the strain rate. Based on the dislocation dynamics theory, a viscoplastic dynamic constitutive model for the 6008 aluminum alloy is constructed. The model accurately describes and predicts the mechanical behavior of this material under impact compression at room temperature.

Bearing of structural anisotropy on deformation and mechanical response of rocks: An experimental example of rocksalt deformation under variable compression rates

The deformation and mechanical responses of rocks are prime concern in development of varieties of civil and mining engineering structures. The deformation and mechanical properties of both natural and artificial materials are strongly depend on mineral constituents and their arrangements, temperatures and pressures, stress rates and structural anisotropy. This study elaborates an understanding of structural anisotropy, compression rates and mechanical attributes relationship in rocks with specific examples of deformed rocksalt. The cubical samples (5X5X5 cm3) with three kinds of structural anisotropy were subjected to quasistatic compressive stress at rates 0.00035 MPa/min, 0.0035 MPa/min, 0.035 MPa/min, 0.35 MPa/min, 3.5MPa/min, 5 MPa/ min, 7MPa/min and 9 MPa/min on servo-controlled Material Testing System (MTS). The stress-strain curves prepared from deformation of rocksalt’s samples under different rates of compressions are used to determine major mechanical parameters viz., strengths, strains, and modulus of elasticity. A micromechanical en-echelon crack array model is proposed to explain the influence of structural anisotropy on deformation patterns and mechanical properties of rocksalt.According to the proposed model the deformation progresses due to different proportional contributions of tensile and shear crack arrays under the influence of structural anisotropy. The control of structural anisotropy loses with respect to increment in rate of compression with enhance contribution of shear crack arrays in comparison to tensile crack arrays and ultimately fails in shear where the structurally anisotropic rock show isotropic behaviour.

Compressive mechanics of warp-knitted spacer fabrics. Part II: a dynamic model

This part presents a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions using quasi-static compressive stress–strain data. The model was established based on a nonlinear mass-spring-damper system by considering spacer yarns as nonlinear springs with damping effect and representation of their stiffness by the constitutive model developed in Part I. Based on the dynamic model, the impact compressive responses of a typical warp-knitted spacer fabric was parametrically studied in terms of damping ratio, initial velocity, striker mass and contact area. The study indicates that damping can reduce the peak acceleration and peak displacement regardless of loading conditions, and the increase of the initial velocity can enhance the damping effect. Increasing initial velocity or striker mass while keeping the counterpart constant can increase the peak acceleration and peak displacement. However, at a constant kinetic energy, either increasing striker mass or decreasing initial velocity can reduce the peak acceleration, but the peak displacement keeps constant. The study also shows that an optimal size of the spacer fabric exists for achieving minimal peak acceleration under impact at a certain kinetic energy. Experimental validation by drop-weight impact tests demonstrates that the predictions of the dynamic model are in satisfactory agreement with the experimental results. Using the quasi-static compressive data from a simple test, this dynamic model can numerically simulate the full time-response of warp-knitted spacer fabrics under various impact conditions.

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al2O3 hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10−3 s−1 using a conventional load frame to 1720 s−1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.

Compressive response of glass fiber composite sandwich structures

Sandwich panels with crushable foam cores have attracted significant interest for impulsive load mitigation. We describe a method for making a lightweight, energy absorbing, glass fiber composite sandwich structure and explore it is through thickness (out-of-plane) compressive response. The sandwich structure utilized corrugated composite cores constructed from delamination resistant 3D woven E-glass fiber textiles folded over triangular cross section prismatic closed cell, PVC foam inserts. The corrugated structure was stitched to 3D woven S2-glass fiber face sheets and infiltrated with a rubber toughened, impact resistant epoxy. The quasi-static compressive stress–strain response of the panels was experimentally investigated as a function of the strut width to length ratio and compared to micromechanical predictions. Slender struts failed by elastic (Euler) buckling which transitioned to plastic microbuckling as the strut aspect ratio increased. Good agreement was observed between experimental results and micromechanical predictions over the wide range of core densities investigated in the study.

Compression behavior of Al2O3k/Al composite materials fabricated by counter-gravity infiltration casting

Al2O3k/Al composite materials were produced using alumina hollow particles as pore-forming materials through the counter-gravity infiltration casting system. Mechanical properties of Al2O3k/Al composite materials under quasi-static compressive load were studied. The experimental results show that the quasi-static compressive stress–strain curves of Al2O3k/Al composite materials include three distinct regions: the linear elastic region, the yield platform region and the densification region. Compared with aluminum foam, the yield stress and plateau stress of Al2O3k/Al composite material are much greater, and the densification strain is reduced relatively. This may be due to the fact that Al2O3k/Al composite materials have the characteristics of both plastic material and brittle material. The alumina hollow particle size and the void content are the key influencing factors for the compression performance such that with the decrease of the particle size and the void content, the yield stress and plateau stress increase gradually.

Elastic moduli and mechanical properties of bulk metallic glasses after quasi-static compression

The effect of quasi-static compressive stress on the elastic moduli and mechanical properties of a Cu 46Zr 46Al 8 bulk metallic glass (BMG) was investigated. When the applied quasi-static stress is below 2 GPa (equivalent to 1.4 times the yield strength of the BMG), the elastic moduli of the deformed BMGs are found to decrease with the applied stress, revealing the softening or dilatation of the bulk metallic glass. The Poisson ratio is relatively stable when the stress is below 1000 MPa, but it decreases significantly afterwards. Both the plasticity and strength of the BMG are found to increase at low applied stress, and achieve a maximum value before decreasing at higher applied stress. The applied stress is shown to enhance the mechanical properties of the BMG and the properties can be controlled by quasi-static compressive stress. The results demonstrate that an applied stress far below the macroscopic yield strength can still result in microscopic yielding and microstructure change in metallic glass systems.

Quasi-static compressive property of metallic glass/porous tungsten bi-continuous phase composite

A metallic glass/porous tungsten bi-continuous phase composite was prepared by pressure infiltration whose quasi-static compressive stress and strain to macroscopic failure are much higher than those of all the previous tungsten-reinforced metallic glass matrix composites. It deserves to be mentioned that because of its high-yield strength and high elastic strain limit, metallic glass seems to be used as the reinforcement to strengthen the crystalline materials in the bi-continuous phase composite materials.