Deformation brittle

When a stress Le. a force per unit area) is applied to a solid, for example it is stretched, sheared, twisted or squashed, it deforms, i.e. changes its length, or shape. For small deformations, the amount of deformation is proportional to the applied stress. The material is said to behave elastically. Beyond a certain deformation (the elastic limit) the material ceases to be elastic, and the material no longer returns to its initial shape when the stress is removed. This is called plastic deformation. If the material is deformed further then it will eventually break. Some materials, such as rubber, are elastic for large deformations, while others, such as plasticine, have a relatively small elastic limit but can then undergo large plastic deformations. Brittle materials, such as china, can only withstand small deformations before they break. 

The cause of brittle fracture in polymers is the inability of the material to quickly dissipate by molecular relaxation processes the internal stresses generated as a result of the imposed deformation. Brittle fracture occurs when the time to failure is the same order of magnitude (or faster) than the speed of the relaxation process that dominates the mechanical behavior in the temperature range of interest. The relevant relaxation processes are the first T < Tg secondary relaxation (p or y). A qualitative criterion for determining whether the relaxation... 

Mechanisms of Any plastic deformation of crystalline ceramics is a result of dislocation motion the Plastic Deformation brittleness of these materials is explained, in part, by the limited number of operable slip systems. 

C, b.p. 907"C, d 713. Transition element occurring as zinc blende, sphalerite (Zn,Fe)S calamine or smithsonite (ZnCO j), willemite (Zo2Si04), franklinite (ZnFe204). Extracted by roasting to ZnO and reduction with carbon. The metal is bluish-white (deformed hep) fairly hard and brittle. Burns... 

Fault traps which are the result of brittle crustal deformations... 

As discussed in Section 2.0 (Exploration), the earth s crust is part of a dynamic system and movements within the crust are accommodated partly by rock deformation. Like any other material, rocks may react to stress with an elastic, ductile or brittle response, as described in the stress-strain diagram in Figure 5.5. 

As it was determined by the test, the stretch diagram at the uniaxial load carrying ability of the carbon plastic UKN-5000 is almost linear until the destruction point. The samples are breaking brittle, and the relative deformation is small (E < 2%). 

Substances in this category include Krypton, sodium chloride, and diamond, as examples, and it is not surprising that differences in detail as to frictional behavior do occur. The softer solids tend to obey Amontons law with /i values in the normal range of 0.5-1.0, provided they are not too near their melting points. Ionic crystals, such as sodium chloride, tend to show irreversible surface damage, in the form of cracks, owing to their brittleness, but still tend to obey Amontons law. This suggests that the area of contact is mainly determined by plastic flow rather than by elastic deformation. 

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

Elastic Behavior The assumption that displacement strains will produce proportional stress over a sufficiently wide range to justify an elastic-stress analysis often is not valid for nonmetals. In brittle nonmetallic piping, strains initially will produce relatively large elastic stresses. The total displacement strain must be kept small, however, since overstrain results in failure rather than plastic deformation. In plastic and resin nonmetallic piping strains generally will produce stresses of the overstrained (plasfic) type even at relatively low values of total displacement strain. 

Hiestand Tableting Indices Likelihood of failure during decompression depends on the abihty of the material to relieve elastic-stress by plastic deformation without undergoing brittle fracture, and this is time dependent. Those which relieve stress rapidly are less... 

FIG. 20-80 Heckel profiles of the unloaded relative compact density for (1) a material densifying by pure plastic deformation, and (2) a material densifying with contributions from brittle fragmentation and particle rearrangement. 

In this chapter, we will review the effects of shock-wave deform.ation on material response after the completion of the shock cycle. The techniques and design parameters necessary to implement successful shock-recovery experiments in metallic and brittle solids will be discussed. The influence of shock parameters, including peak pressure and pulse duration, loading-rate effects, and the Bauschinger effect (in some shock-loaded materials) on postshock structure/property material behavior will be detailed. 

---