Strain impact

Polymer Melting point (°C) Glass transition (°C) Vicat A (°C) Young s modulus (GPa) Tensile strength (MPa) Strain (%) Impact strength (Izod) (J/m) Density (g/cm)... 

Most unusual and initially most surprising was the amount of plastic strain measured in impacted RDX crystals. RDX is usually regarded as a brittle crystal which fractures at about 10 % strain. Impact on 50 to 100 mg of poly-crystalline RDX samples by a 10 kg free falling drop weight released from a height of about. 2 m formed disc shaped samples about 15 mm in diameter and. 1 mm thick. The surfaces of the impactor and the anvil on which the sample was placed were... 

Creep rupture strength experiments have been conducted in the ZEMAK I - IV laboratory facilities in Julich. Fig. 2-15 shows some measurement results. Also fatigue tests with periodic stress - strain impact have been made to simulate load changes. 

Licea-Claverie and co-workers [57] studied mechanical stress-strain, impact properties and also thermal properties of PA 6,6 (including some recycled PA) with mixed glass fibre and carbon fibre reinforcements and compared these properties with those of the virgin polymers. No dependence on mechanical properties because of increasing amounts of scrap in the composites was found up to 10.4 wt%. The recycled composites generally showed lower mechanical properties when compared with the virgin composites because of a poor matrix-fibre adhesion. 

For safety considerations the amplitude of the pressure wave induced by those fast propagating flames is a direct measure of the strains impacting buildings and industrial facilities in case of an accident. The maximum overpressure values measured at the channel side walls in the model experiments are presented in Fig. 17 as a function of the local propagation velocity. 

Some of the more important methods of failure studies include stress-strain, impact loading, and fatigue. Creep and stress relaxation (Chapter 10) may cause serious damage to engineering materials, but they normally do not result in fracture per se except for creep rupture. Emphasis in this chapter will be on the study of fracture energy, kinetics of crack growth, and molecular mechanisms. The reader is directed to Chapter 13 for a fuller discussion of plastic toughening. 

Mechanical properties also degrade as a result of crack formation. Tensile strength, strain, impact toughness, and flexural strength change [83]. 

Hardness, Impact Strength. Microhardness profiles on sections from explosion-bonded materials show the effect of strain hardening on the metals in the composite (see Hardness). Figure 8 Ulustrates the effect of cladding a strain-hardening austenitic stainless steel to a carbon steel. The austenitic stainless steel is hardened adjacent to the weld interface by explosion welding, whereas the carbon steel is not hardened to a great extent. 

Mechanical properties of mbber-modifted epoxy resins depend on the extent of mbber-phase separation and on the morphological features of the mbber phase. Dissolved mbber causes plastic deformation and necking at low strains, but does not result in impact toughening. The presence of mbber particles is a necessary but not sufficient condition for achieving impact resistance. Optimum properties are obtained with materials comprising both dissolved and phase-separated mbber (305). 

Minimills and other EAF plants ate expanding iato flat-roUed steel products which, by some estimates, requite 50—75% low residual scrap or alternative raw material. Up to 16 million t of new capacity are expected to be added ia the United States between 1994 and 2000 (18). Developments ia other parts of the world also impact scrap use and supply. Possible scrap deficiencies of several million tons have been projected for EAFs ia East Asia and ia parts of Europe. This puts additional strains on the total scrap supply, particularly low residual scrap (19,20). The question of adequate supply of low residual scrap is always a controversial one. Some analysts see serious global shortages ia the first decade of the twenty-first century others are convinced that the scrap iadustry has the capabiUty to produce scrap ia the quantities and quaUty to meet foreseeable demand. This uncertainty ia combination with high scrap prices has led to iacreased use of scrap alternatives where the latter is price competitive with premium scrap. Use of pig iroa has iacreased ia EAF plants and mote capacity is being iastaHed for DRI and HBI outside the United States. 

Impact and Erosion. Impact involves the rapid appHcation of a substantial load to a relatively small area. Most of the kinetic energy from the impacting object is transformed into strain energy for crack propagation. Impact can produce immediate failure if there is complete penetration of the impacted body or if the impact induces a macrostress in the piece, causing it to deflect and then crack catastrophically. Failure can also occur if erosion reduces the cross section and load-bearing capacity of the component, causes a loss of dimensional tolerance, or causes the loss of a protective coating. Detailed information on impact and erosion is available (49). 

Proportion of Hard Segments. As expected, the modulus of styrenic block copolymers increases with the proportion of the hard polystyrene segments. The tensile behavior of otherwise similar block copolymers with a wide range of polystyrene contents shows a family of stress—strain curves (4,7,8). As the styrene content is increased, the products change from very weak, soft, mbbedike materials to strong elastomers, then to leathery materials, and finally to hard glassy thermoplastics. The latter have been commercialized as clear, high impact polystyrenes under the trade name K-Resin (39) (Phillips Petroleum Co.). Other types of thermoplastic elastomers show similar behavior that is, as the ratio of the hard to soft phase is increased, the product in turn becomes harder. 

Impact testing is not required if the design temperature is helow —29 C (—20 F) hut at or above —46 C (—50 F) and the maximum operating pressure of the fabricated or assembled components will not exceed 25 percent of the maximum allowable design pressure at ambient temperature and the combined longitudinal stress due to pressure, deadweight, and displacement strain (see Par. 319.2.1) does not exceed 41 MPa (6000 Ibfiin ). 

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