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模具英文资料% U/ l+ k# q: c% G: d/ u5 H" u
Material properties for part design X* j3 S; k7 X- T& z- o0 x( }
Plastics are sensitive to operating conditions
) \1 k& z! }8 d1 y3 y1 t# TThe plastics molding processes allow parts designers more freedom than working with % e( k+ j3 M0 F9 B5 i. S) L* `9 I
metals because plastics materials are so versatile. Unlike metals, however, the * _& d: f# J4 }- g+ ^5 S
mechanical properties of plastics are very sensitive to the type, rate, duration, and & y6 T' r# d5 q
frequency of loading, the change in operating temperature, and in some cases, relative ( q% O. ]1 `2 }
humidity. The plastics part designer must take a material's response to these conditions % b& c3 a9 c9 i
into account. The table below lists the five typical loading and operating conditions, - o% i. ?& g5 S; M/ E. s
together with the relevant material properties a designer needs to consider. " }) m' M! o- A5 v' {5 o
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+ }/ F& {9 `8 m: t6 e6 w2 uTABLE 1. Typical loading/operating conditions together with the relevant ' o# x) R6 {4 X7 o. {. V* s
material properties
4 H$ [2 f/ b7 c! W2 `5 hLoading/operating conditions. Relevant material properties.
/ |! [* Y- ], e) T4 wShort-term loading. Stress-strain behavior.
2 ?+ d/ U- }# b# ZLong-term loading. Creep and stress relaxation.
8 ~7 Y8 K% ]# M0 r3 r& Y4 pRepeated loading. Fatigue.
1 J+ ^4 _2 T9 i5 v+ h; q o8 Y/ u9 c& k kHigh velocity and impact loading. Impact strength. ! ~2 t# ]" ^$ a% j1 s' h9 g& q$ Y' }
Loading at extreme temperatures. Thermal mechanical behavior.
5 |& @& p4 ?6 B" u! q3 IStress-strain behavior
- G% L4 n1 l' @Part strength & k4 b' B' m8 H3 E6 c9 A- V
The stress-strain behavior of a material determines the material contribution to part strength (or
! Y2 E2 l# Q" c9 astiffness), the relationship between load and deflection in a plastic part. Other factors that affect part ( z8 D! X, T' Y5 c/ q
strength include part geometry, loading, constraint conditions on the part, and the residual stresses
+ C# E9 f5 G: { F! C* X& P+ _and orientations that result from the molding process. There are various types of strength, such as
; i" K$ {2 B' q: I! Ftensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions / J5 B5 ?3 _. m/ N
the part is subjected to. These types also correspond to the primary load state present in the part. The 0 Y; Y3 h5 j4 ?& Y G. _
stress-strain behavior of the material in the same mode as the primary load state in the part is most
& U, E5 L0 ] A/ Trelevant in determining part strength. |
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