The National Science Fair

Designing Machine

The importance of elastic range in designing machine Within the elastic range, the limiting value stress and strain are proportianal, is called the limit of proportionality Ap. In this region, the metal obeys hooker s law, whirh states that the stress is proportional to strain in the caastir rangy of loading, f.the material completely regains its original dimensions after the load is removed. In the current plotting of the curare, the proportionality limit is obtained at a slightly lower value of the load than the caastir limit. This may be attributed to the time-lagin the were of the original dimensicyns of the material. This effect is very frequently noticed in Some non-ferrvous metals.

Which Iran and nickel exhibit clear ranges of elastirity, copper, zinc, tin, found to be imperfectly elastic even at relatively low values low values q:. Actually the elastic limit is distinguishable from rhe proportionaily limit more clearly depznding upon the sensitivity of the from the proportionality measnringInstrument distinguishable. When the load is increased beyond the elastic limit, plastic deformation starts. sirnultaneously the specimen gets work-hardened. A point is reached wYlen the deformation starts to occur more rapidly than the increasing load. This point is called they yield point Q.

the metal which was resisting the load till then, starts to deform somewhat rapidly, i, e… yield. The yield stress 15 called yield llmlt Ay. The elongation of the specimen continues from to S and then to T. The stress-strain relation in this period is indicated by tile flow plastic portion of the curvr QRST. At the specimen breaks, and this load is called the breaking load. The value of maximun load S dividid by the original cross-sectional area of the specimsm is referred to as the ultimate tensile strength of the metal or simply the tensile strength Au. Logically speaking, once the elastic limit is exceeded, the metal should start to yield, and finally break, without any increase: in the value of 5trvss. But the curve records an increased StreSS even after the elastic limit is exceeded. Two reasons can be given far tliia behavior: 1. The strain hardening of the material: 2. The diminishing cross-sectional area of the specimen, suffervd an acctount EP. plastic defvrmalivn. The more plastic deformation the metal undergoes, tile harder it becomes, dut to work-hardening. The more dm metal gets elongated the more its diarrleter (and hence. cross-sectional area is decreased This continues until the point S is reached.) After S, the rate at which the reductian in area takes place, exceeds the rate at which the stress increases. Fxcvlnes so high that the reduction in area begins to strain produces a Incaiixed effect at some point. This is called necking. Reduction in cross-sectinnal area takes place rapidly that the load value actually drops. This is indicated by ST. failure occurs to this point T. We provide Professional technology, excellent product quality and intimate after-sales service when you purchase Stone production line, Hammer crusher, from our company.