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模具英文资料/ y7 M" X% G( c
Material properties for part design % C6 l, O( T" o7 Y
Plastics are sensitive to operating conditions 4 Q$ Z& N) C) N! Z
The plastics molding processes allow parts designers more freedom than working with . R- q4 w3 P7 P% \; L$ U; _+ e
metals because plastics materials are so versatile. Unlike metals, however, the 9 h. g% D# T3 D: ?4 S O
mechanical properties of plastics are very sensitive to the type, rate, duration, and & @% v6 \- r# t+ D
frequency of loading, the change in operating temperature, and in some cases, relative " T; M9 D9 @( t: I
humidity. The plastics part designer must take a material's response to these conditions 1 j& q2 M6 j" y3 w8 F# e
into account. The table below lists the five typical loading and operating conditions,
+ _! a+ H# n d) C2 ~- wtogether with the relevant material properties a designer needs to consider. * V) Z5 _! d0 |
. % l; ^: ^& a4 ?( d* k) M
TABLE 1. Typical loading/operating conditions together with the relevant
7 X# c |& K4 Z3 l5 \material properties
! h& o1 D% J: V KLoading/operating conditions. Relevant material properties. 7 \- I, t* S. x# A
Short-term loading. Stress-strain behavior. 9 n( }* Q; s* T. j: _0 q: _) ^6 @
Long-term loading. Creep and stress relaxation. 6 _; Z: g) t7 L( ~) ?9 v
Repeated loading. Fatigue.
& s6 n" F1 P1 z' cHigh velocity and impact loading. Impact strength.
1 W8 s" }- @2 |Loading at extreme temperatures. Thermal mechanical behavior. - G% A4 k( @/ u6 A7 e
Stress-strain behavior
3 t' `5 H9 g0 ~+ k1 o' `/ K3 ZPart strength
" B8 n N; P# M4 C5 Y1 j& V2 @( q3 eThe stress-strain behavior of a material determines the material contribution to part strength (or 5 N) T$ ?9 e9 D" j: U
stiffness), the relationship between load and deflection in a plastic part. Other factors that affect part ) \' O; H w, x/ }. [
strength include part geometry, loading, constraint conditions on the part, and the residual stresses
, t- _# \0 n, n+ g, v% U" Uand orientations that result from the molding process. There are various types of strength, such as ' \% A. P' x% A% x& D
tensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions
/ Y2 U; ?$ Y8 t) j3 J6 u X( Y( r. qthe part is subjected to. These types also correspond to the primary load state present in the part. The
* i7 s# H; N7 J7 ^+ P5 `stress-strain behavior of the material in the same mode as the primary load state in the part is most
0 y; _5 Y% G$ M# J5 {relevant in determining part strength. |
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发表于 2007-5-31 11:12:28