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模具英文资料- @: k" e8 \7 B6 k% ?0 W1 b/ i7 E
Material properties for part design 7 R! ^7 F! A, ~
Plastics are sensitive to operating conditions
, K& @ e7 i/ w/ E; o, o4 RThe plastics molding processes allow parts designers more freedom than working with - O, q' O( m/ q1 G( X; W$ p3 B# c
metals because plastics materials are so versatile. Unlike metals, however, the
7 s6 F( ^! J. {mechanical properties of plastics are very sensitive to the type, rate, duration, and . q- U9 g: u. A& T7 R. N \
frequency of loading, the change in operating temperature, and in some cases, relative 2 V0 G- }! J) A9 n: U2 y, A
humidity. The plastics part designer must take a material's response to these conditions ) C8 |: }* R5 U' g: X
into account. The table below lists the five typical loading and operating conditions, s+ X' F( u: }' v3 E$ z
together with the relevant material properties a designer needs to consider.
9 s+ d; s F% I2 ?, O$ H.
, Y! U% a" I. c) V1 H. {5 ?$ pTABLE 1. Typical loading/operating conditions together with the relevant
! J4 M0 k+ l+ L# S* \7 Vmaterial properties 5 x$ Q5 D8 Z9 e8 Q4 r' L7 k; d
Loading/operating conditions. Relevant material properties. F; p8 J: O! u5 c) l0 o r
Short-term loading. Stress-strain behavior. - j# s0 q2 K9 ~7 T j' Q" a
Long-term loading. Creep and stress relaxation. " A+ V- N" Q8 E. K5 `0 |
Repeated loading. Fatigue.
5 u. F3 t" Q, v6 j/ ]High velocity and impact loading. Impact strength.
- N" j6 e' ]9 ?) d5 uLoading at extreme temperatures. Thermal mechanical behavior. 6 [. q- |2 Q) N+ K) @
Stress-strain behavior
1 E, ?/ K/ D4 o& x5 Z, QPart strength
\& Y% g, s, e( G$ ^+ B/ u; rThe stress-strain behavior of a material determines the material contribution to part strength (or ( `' s. F8 E6 [, G' S; I- c* S
stiffness), the relationship between load and deflection in a plastic part. Other factors that affect part
; x2 T+ E% j* n5 ^! lstrength include part geometry, loading, constraint conditions on the part, and the residual stresses
9 R8 y. ]' \4 F$ D6 E$ \1 z: Hand orientations that result from the molding process. There are various types of strength, such as
! S" q5 M" w/ `tensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions
2 c9 Z7 q3 q# l$ K: ?# lthe part is subjected to. These types also correspond to the primary load state present in the part. The 6 E$ p9 f; c- u
stress-strain behavior of the material in the same mode as the primary load state in the part is most ! W: `0 @9 J5 M2 B6 f" C
relevant in determining part strength. |
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发表于 2007-5-31 11:12:28