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模具英文资料) r$ p, U9 f( ]) V6 t2 r
Material properties for part design * R5 x$ B- e' x# T2 ^7 P! O
Plastics are sensitive to operating conditions 1 x' e9 @/ N) w
The plastics molding processes allow parts designers more freedom than working with
. z9 q3 L7 L+ m; ^# E" @metals because plastics materials are so versatile. Unlike metals, however, the / r" o% a1 F+ _4 V& c9 k7 K. z9 r
mechanical properties of plastics are very sensitive to the type, rate, duration, and x1 V. {1 M# S8 n: b
frequency of loading, the change in operating temperature, and in some cases, relative ) S1 q8 A8 S, V2 b& T
humidity. The plastics part designer must take a material's response to these conditions 2 r) p2 D( \+ C u$ C
into account. The table below lists the five typical loading and operating conditions, / D+ t" p2 X) K7 v2 U& V% U
together with the relevant material properties a designer needs to consider.
5 Y y! N7 u a$ U+ U9 b. + E; A3 W2 R1 n0 J( H4 T2 v3 ]
TABLE 1. Typical loading/operating conditions together with the relevant
J' d, D6 d% Bmaterial properties $ f- q1 ^. A) m1 u: j: l2 z- Z2 m
Loading/operating conditions. Relevant material properties. : }% L. l3 M5 d; \8 a/ h0 i
Short-term loading. Stress-strain behavior.
: k; f/ w7 Z8 RLong-term loading. Creep and stress relaxation.
( \, \# _- u6 i0 A/ O' w0 N* r1 WRepeated loading. Fatigue.
. ]+ {7 U0 F8 u5 _4 eHigh velocity and impact loading. Impact strength. # L4 C% T7 q: j O
Loading at extreme temperatures. Thermal mechanical behavior.
# b& u4 d, J; E+ Y ^Stress-strain behavior
6 p% c+ k" S5 H9 gPart strength
2 T+ [, \0 u x* WThe stress-strain behavior of a material determines the material contribution to part strength (or 8 d7 K1 i6 P) l8 n0 h! S! n4 Y9 V
stiffness), the relationship between load and deflection in a plastic part. Other factors that affect part & w) w' d' e) H! R
strength include part geometry, loading, constraint conditions on the part, and the residual stresses
/ m: o6 z8 v7 `, _ R. g8 u$ |and orientations that result from the molding process. There are various types of strength, such as 0 |; F/ p( e4 M) }3 ~5 _
tensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions
+ y* \' M( v- c J- ?* s& _$ Wthe part is subjected to. These types also correspond to the primary load state present in the part. The
4 y& f5 D6 n5 R3 c+ [stress-strain behavior of the material in the same mode as the primary load state in the part is most
) R3 U9 P8 `; Qrelevant in determining part strength. |
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发表于 2007-5-31 11:12:28