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模具英文资料% |' X3 |. A f# ~5 a6 q7 e( t+ E
Material properties for part design , h2 W; o9 y) s, ]6 b! {
Plastics are sensitive to operating conditions $ S1 P8 r+ U0 O7 U- S# J4 m
The plastics molding processes allow parts designers more freedom than working with 1 c9 o/ ?/ \; k$ J( x# i2 |3 V
metals because plastics materials are so versatile. Unlike metals, however, the
9 I8 u' l$ g$ h9 c& Tmechanical properties of plastics are very sensitive to the type, rate, duration, and
2 {1 F/ G5 Z8 Zfrequency of loading, the change in operating temperature, and in some cases, relative * C' L' |5 R8 G8 C
humidity. The plastics part designer must take a material's response to these conditions , N! H1 n1 B$ h1 J
into account. The table below lists the five typical loading and operating conditions, ! Y- _; R- W# M$ \: y/ y/ I
together with the relevant material properties a designer needs to consider. 3 [& H+ o' K5 `5 T& \+ ]
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TABLE 1. Typical loading/operating conditions together with the relevant / ~, u4 M0 y4 I# m( O4 `% ]
material properties
$ C8 r9 _: P: [4 aLoading/operating conditions. Relevant material properties. " S( |* v) E* t* s; v
Short-term loading. Stress-strain behavior.
( n, B3 }3 I/ J, Q% W1 ]Long-term loading. Creep and stress relaxation. $ ~& I# x4 I; B
Repeated loading. Fatigue. : f) x, {! s: [3 e. w7 y% t
High velocity and impact loading. Impact strength.
! c$ f1 o+ j- F6 r( e/ k4 R" s+ ELoading at extreme temperatures. Thermal mechanical behavior.
& ?* O9 o- t& O3 T' hStress-strain behavior # g9 v8 C/ n! i# Q
Part strength
1 J! _( i3 U- ]5 wThe stress-strain behavior of a material determines the material contribution to part strength (or
* E: q- {& E. y9 \6 P9 \6 ^9 k" estiffness), the relationship between load and deflection in a plastic part. Other factors that affect part
$ M. C" ~, m6 R* Y5 B6 h& Istrength include part geometry, loading, constraint conditions on the part, and the residual stresses
6 r! G- n; ~8 S9 h* U) cand orientations that result from the molding process. There are various types of strength, such as
) B, t: d ?# n+ K- ?tensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions & U4 j$ T3 q' \! n4 \9 [
the part is subjected to. These types also correspond to the primary load state present in the part. The
6 D4 T, ~4 l* Y) T bstress-strain behavior of the material in the same mode as the primary load state in the part is most
( u8 L. j) b/ D9 ]3 Mrelevant in determining part strength. |
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发表于 2007-5-31 11:12:28