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模具英文资料* M& \1 ~! Q" A+ @* D5 w r
Material properties for part design . \3 G/ V: Y- X: m6 e+ X# l
Plastics are sensitive to operating conditions
2 T# k; p. ?6 o! g6 RThe plastics molding processes allow parts designers more freedom than working with
' z* }3 k6 Y& x6 }! h; X) Nmetals because plastics materials are so versatile. Unlike metals, however, the
: {( t9 K) ?1 l K* w1 jmechanical properties of plastics are very sensitive to the type, rate, duration, and
2 f" n! a6 Y1 T' mfrequency of loading, the change in operating temperature, and in some cases, relative
3 C7 L$ D! D' K8 @+ _9 Whumidity. The plastics part designer must take a material's response to these conditions
% D. i% j( s7 T% ?+ O4 ]0 z4 M" Jinto account. The table below lists the five typical loading and operating conditions,
+ \( \0 _; S* |together with the relevant material properties a designer needs to consider.
7 W# t2 z& F9 A7 [" |1 c b- t$ H5 Y. i.
4 O4 d) D! E5 J! o4 yTABLE 1. Typical loading/operating conditions together with the relevant
0 u, x' X+ c# H% \; \' l$ c v# Q+ xmaterial properties
$ O/ k7 G6 h' S& q/ A" ^Loading/operating conditions. Relevant material properties.
5 M S8 ^* L: b! l" _+ bShort-term loading. Stress-strain behavior.
# p6 h; b, D! M$ vLong-term loading. Creep and stress relaxation. # ` e- T" O! u8 H! i/ d+ |
Repeated loading. Fatigue.
1 ~# j, _- T, x, a+ W0 A9 eHigh velocity and impact loading. Impact strength.
) k* a. V: k+ z9 C/ p1 ?$ ILoading at extreme temperatures. Thermal mechanical behavior. " \ a5 ~0 j N1 j
Stress-strain behavior ' [4 ?" @: _9 K2 K
Part strength
* d) K D1 ~4 l+ e3 mThe stress-strain behavior of a material determines the material contribution to part strength (or
& V# `: s8 W, C( M* R0 dstiffness), the relationship between load and deflection in a plastic part. Other factors that affect part $ S$ R8 A% `- H; h$ O; e
strength include part geometry, loading, constraint conditions on the part, and the residual stresses # G! O/ i! ~# R5 W. |! x
and orientations that result from the molding process. There are various types of strength, such as
% ]8 H5 z# X, H9 T. h7 q! y8 w/ ytensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions 4 y+ q0 E$ _7 i' q( P3 n2 x3 g
the part is subjected to. These types also correspond to the primary load state present in the part. The
' F% K i& E$ h7 R/ g, ? qstress-strain behavior of the material in the same mode as the primary load state in the part is most 1 ?. C, l. P+ Q. \+ b
relevant in determining part strength. |
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