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Brittle materials strain

The parameters for the model were originally evaluated for oil shale, a material for which substantial fracture stress and fragment size data depending on strain rate were available (see Fig. 8.11). In the case of a less well-characterized brittle material, the parameters may be inferred from the shear-wave velocity and a dynamic fracture or spall stress at a known strain rate. In particular, is approximately one-third the shear-wave velocity, m has been shown to be about 6 for various brittle materials (Grady and Lipkin, 1980), and k can then be determined from a known dynamic fracture stress using an analytic solution of (8.65), (8.66) and (8.68) in one dimension for constant strain rate. [Pg.315]

Consequently, changing the temperature or the strain rate of a TP may have a considerable effect on its observed stress-strain behavior. At lower temperatures or higher strain rates, the stress-strain curve of a TP may exhibit a steeper initial slope and a higher yield stress. In the extreme, the stress-strain curve may show the minor deviation from initial linearity and the lower failure strain characteristic of a brittle material. [Pg.45]

Brittleness Brittle materials exhibit tensile stress-strain behavior different from that illustrated in Fig. 2-13. Specimens of such materials fracture without appreciable material yielding. Thus, the tensile stress-strain curves of brittle materials often show relatively little deviation from the initial linearity, relatively low strain at failure, and no point of zero slope. Different materials may exhibit significantly different tensile stress-strain behavior when exposed to different factors such as the same temperature and strain rate or at different temperatures. Tensile stress-strain data obtained per ASTM for several plastics at room temperature are shown in Table 2-3. [Pg.52]

It should be recognized that tensile properties would most likely vary with a change of speed of the pulling jaws and with variation in the atmospheric conditions. Figure 2-14 shows the variation in a stress-strain curve when the speed of testing is altered also shown are the effects of temperature changes on the stress-strain curves. When the speed of pulling force is increased, the material reacts like brittle material when the temperature is increased, the material reacts like ductile material. [Pg.309]

It should be noted that test information would vary with specimen thickness, temperature, atmospheric conditions, and different speed of straining force. This test is made at 73.4°F (23°C) and 50% relative humidity. For brittle materials (those that will break below a 5% strain) the thickness, span, and width of the specimen and the speed of crosshead movement are varied to bring about a rate of strain of 0.01 in./in./min. The appropriate specimen size are provided in the test specification. [Pg.311]

Selenrath, Th. R. Gramberg, J. (1958). Stress-strain relations and breakages of rocks. In Walton, W. H. (ed.) Mechanical Properties of Non-metaUic Brittle Materials, Chapter 6, pp. 79-105. London Butterworths. [Pg.384]

Concrete is an inherently brittle material with low tensile strength and strain capacities. Its brittle characteristics lead to easy nucleation and propagation of cracks, thus restricting its range of applications. To address this deficiency, fibers of different materials such as asbestos, glass, metal, and synthetics " are used as additives, with the following results"" ... [Pg.255]

In terms of the mechanical behavior that has already been described in Sections 5.1 and Section 5.2, stress-strain diagrams for polymers can exhibit many of the same characteristics as brittle materials (Figure 5.58, curve A) and ductile materials (Figure 5.58, curve B). In general, highly crystalline polymers (curve A) behave in a brittle manner, whereas amorphous polymers can exhibit plastic deformation, as in... [Pg.448]

Majerus (61, 62) has approached the failure behavior of highly filled polymers by a thermodynamic treatment in which the ability to resist rupture is related to the propellant s ability to absorb and dissipate energy at a certain rate. An energy criterion which requires failure to be a function of both stress and strain was originally stated by Griffith (36) for brittle materials and later adapted to polymers by Rivlin and Thomas (80). Williams (115) has applied an energy criterion to viscoelastic materials such as solid propellants where appropriate terms are included for viscous energy dissipation. [Pg.230]

Sulphur concretes have undergone substantial development in the last six years. Recent effort has been directed towards improved durability and less brittle stress-strain behaviour has been achieved. A technology has been developed to produce a material (Sudicrete) with the same stress strain behaviour after three years as that observed soon after casting. Other materials show a consistent reversion to brittle behaviour with time. Nevertheless, there is considerable room for improvement in mix design. [Pg.152]

Elasticity. Glasses, like other brittle materials, deform elastically until they break in direct proportion to the applied stress. The Youngs modulus E is the constant of proportionality between the applied stress and the resulting strain. It is about 70 GPa (107 psi) [(0.07 MPa stress per tm/m strain = (0.07 MPam)/ im)] for a typical glass. [Pg.299]

Fig. l-(b) shows a stress-strain curve for a brittle material such as non-metallic material, (the material that does not conduct electric current), or an intermetallic compound, such as TiFe for which failure occurs before any appreciable plastic deformation. Thus, there is no yield stress or plastic deformation. The fracture strength is essentially at the elastic limit or the yield stress. [Pg.155]

Of course in general the mechanical properties of plastics film and sheet will be rather different from those of metal foil and strip, whether ferrous or non-ferrous, and equipment and conditions may have to be adapted to allow for this. Sometimes cold techniques are modified to take advantage of the thermal properties of plastics but in their simplest forms they are limited to the compounds with which cold working is possible—that is, those of suitable hardness, ductility, and finish—and that can be fed in the forms of sheet, roll, or strip. So as to avoid frequent interruptions of the cycle the stock must be uniform and any strain distributed in a regular manner. Fast processes requiring the application of pressure are not suitable for hard, brittle materials, nor for any produced in such a way as to give concentrations of strain, perhaps in areas that differ with circumstances. [Pg.47]

For brittle materials the stress-strain curves are almost linear up to the fracture point and the fracture strain is small, of the order of a few percentages. Figs. 13.74 and 13.75 show the tensile strain and flexural strength as functions of temperature for PMMA. At 10 °C the fracture strain increases, which points to a transition to ductile behaviour. The brittle... [Pg.466]


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