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模具英文资料
) \8 s4 J0 x& S+ ~) e/ bMaterial properties for part design
) B# |! A# s6 o4 n( t nPlastics are sensitive to operating conditions $ L) P4 v/ Q0 N$ V: Q+ I; ]. Y
The plastics molding processes allow parts designers more freedom than working with
) @8 K9 m6 C1 ?4 v6 }- n& V6 kmetals because plastics materials are so versatile. Unlike metals, however, the
+ o: |) M7 ^) U7 }# L* k. Wmechanical properties of plastics are very sensitive to the type, rate, duration, and
% f% ~, W# i0 }frequency of loading, the change in operating temperature, and in some cases, relative
8 @7 u d/ T( q' \ {$ vhumidity. The plastics part designer must take a material's response to these conditions ' A6 ?( d. S" j
into account. The table below lists the five typical loading and operating conditions,
7 U5 w0 h- \1 t" c5 etogether with the relevant material properties a designer needs to consider.
; \9 d/ J, ]5 |. ' \% f1 b" v ~# {. k! s* d. e/ E' ^
TABLE 1. Typical loading/operating conditions together with the relevant ; l% A z0 U; L; w: R
material properties
2 Y5 d6 K6 O* Z T: |, |8 O C2 zLoading/operating conditions. Relevant material properties.
1 D- F2 c9 A I0 FShort-term loading. Stress-strain behavior.
1 n' C& c, i a% P5 @6 T5 nLong-term loading. Creep and stress relaxation.
- h, ^6 M+ U1 }, Q$ n1 ?; JRepeated loading. Fatigue.
. q; m' \' V* U4 s5 `; `9 Y; ^High velocity and impact loading. Impact strength. ' ~( n7 r4 z4 P' t% I. U
Loading at extreme temperatures. Thermal mechanical behavior. \ B6 d x% c$ O% ]
Stress-strain behavior
% b. a6 g' w. `1 V9 _Part strength
/ j# J% ?# J7 q+ n) LThe stress-strain behavior of a material determines the material contribution to part strength (or ! U6 M6 Q a7 g
stiffness), the relationship between load and deflection in a plastic part. Other factors that affect part
( J( F- r# l, E t0 G$ p# M( ostrength include part geometry, loading, constraint conditions on the part, and the residual stresses 4 o2 P1 F, L- w9 q, h3 }+ Y
and orientations that result from the molding process. There are various types of strength, such as
0 c3 F3 V7 d0 w5 Z, wtensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions
- o: {! s1 M0 {+ G E% Uthe part is subjected to. These types also correspond to the primary load state present in the part. The
; q2 j0 [7 B+ I3 [stress-strain behavior of the material in the same mode as the primary load state in the part is most
4 y+ N2 A5 r: G: X7 M4 w, Trelevant in determining part strength. |
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发表于 2007-5-31 11:12:28