Uniaxial compressive stress

Mills and Gilchrist (270) analysed the heat transfer that occurs when closed cell foams are subjected to impact, to predict the effect on the uniaxial compression stress-strain curve. Transient heat conduction from the hot compressed gas to the cell walls occurs on the 10 ms... 

The effect of gas compression on the uniaxial compression stress-strain curve of closed-cell polymer foams was analysed. The elastic contribution of cell faces to the compressive stress-strain curve is predicted quantitatively, and the effect on the initial Young s modulus is said to be large. The polymer contribution was analysed using a tetrakaidecahedral cell model. It is demonstrated that the cell faces contribute linearly to the Young s modulus, but compressive yielding involves non-linear viscoelastic deformation. 3 refs. 

Gas compression in closed-cell polymer foams was analysed, and the effect on the uniaxial compression stress-strain curve predicted. Results were compared with experimental data for a foams with a range of cell sizes, and the heat transfer conditions inferred from the best fit with the simulations. The lateral expansion of the foam must be considered in the simulation, so in subsidiary experiments Poisson s ratio was measured at high compressive strains. 13 refs. 

The transformation can be influenced by an applied stress. As seen in Fig. 24.13, the stress-free transformation to martensite results in a decrease in specimen length. Data in Figs. 24.14 and 24.15 were obtained by applying a series of constant uniaxial stresses at constant ambient pressure, P. The data show that the transformation temperature increases approximately linearly with applied uniaxial compressive stress. This dependence of transformation temperature on stress state follows from minimization of the appropriate thermodynamic function. For a material under... 

Figure 24.15 shows that the martensitic transformation temperature in the In-Tl system is raised by applying a constant uniaxial compressive stress. Using the thermodynamic formalism leading to Eq. 24.11, develop a Clausius-Clapeyron relationship that relates the observed effect of applied stress on transformation temperature to thermodynamic quantities. 

Curves of uniaxial compressive stress against strain for hep are non-linear and vary somewhat with the strain rate. Caution is therefore needed in comparing values of Young s modulus obtained in different investigations, results obtained at very low stresses by the dynamic method in which a resonance frequency of vibration is determined being higher than ones given... 

In shock behavior, we will only consider compressive stress and strain. Also, to keep the mathematics and models simple, let us only consider uniaxial compressive stress and strain. This means we will be studying these effects along only one axis of a material. We will assume the dimension of the material perpendicular to the strain axis to be infinite. This assumption means that the systems we will study have no edge effects. In Figure 14.2, we follow the same material to a much, much higher level of stress. 

Because easy-flowing powders cannot remain piled as an unconfined structure, allowing small strain changes within, true stress (Equation 6) cannot be used to characterize compression. Thus, the concept of confined uniaxial compression stress has been introduced to help characterize compressive stress in powders. Confined uniaxial compression stress is the force exerted by a piston that compresses a certain powder over the piston area. The powder is generally poured and confined in a container that fits closely to a piston s wall. 

Where a, and a 3 are the maximum and minimum principal effective stress (in the above formula, compression is taken positive, and the principal effective stresses are supposed to be positive), Oc is the uniaxial compressive stress equal to 123 MPa, and m and s are two constants, m = 17.5, s = 0.19. 

Li fin, Chen lie, Jiang Deyi, Yang Chunhe, Liu Chun. 2011. The analysis of surface crack propagation on bedded rock salt under uniaxial compressive stress[J]. Rock and Soil Mechanics, (5) 1394-1398. 

The above solution can also be used if cr is an applied uniaxial compressive stress. In this case, the maximum tensile stress is — cr and the minimum is 3cr. Thus, plates can fail in a tensile mode, even if the plate is in compression. This idea is used extensively in rock mechanics, as most rocks are in a state of compression but can undergo a tensile failure in the vicinity of holes and pores. In general, pores in brittle materials are not expected to be bounded by a smooth surface and the stress concentrations can be much larger. Consider what would happen to the stresses if another circular hole with a much smaller radius was placed at 6= ttI2. This process could be repeated to approximate surface roughness or holes with sharp radii of curvature. It is clear from such a process that the stress concentration would quickly exceed lOcr. As will be shown in Chapter 8, the ability of cracks to concentrate stress is a key aspect in understanding the fracture process. 

Szy] Coereive foree, remanent induction 750°C, 20 at.% Fe, 20 at.% Ni, uniaxial compression stress applied... 

Fig. 1.45 Explosive failure of the S1C-N-UC02 specimen (12.7 mm in diameter and 25.4 mm in length) subjected to the unconfined uniaxial compressive stress condition (iTi = 3988 MPa at failure and 0-2 = (73 = 0) [33]. With kind permission of Professor Brannon...

Vile, G.W.D. A combined stress testing machine for concrete. The Engineer, 1965, (JuL). Newman, K. and Lachance, L. The testing of brittle materials under uniform uniaxial compressive stress. Proceedints of American Society for Testing and Material, 1965, 65. 

The compressive strength of a material is the maximum uniaxial compressive stress (compressive force per unit area) reached when the material fails completely on being subjected to a load that pushes it together. 

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