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模具英文资料7 W4 ~' W u7 u) s
Material properties for part design
2 T1 n7 i$ u( YPlastics are sensitive to operating conditions 0 \0 j$ I) n4 Q4 y" h) i
The plastics molding processes allow parts designers more freedom than working with
4 n7 D6 t3 l* Y' i& p- }8 j! W$ O: nmetals because plastics materials are so versatile. Unlike metals, however, the
, s" W/ p1 S: kmechanical properties of plastics are very sensitive to the type, rate, duration, and + h% M: A. B6 n
frequency of loading, the change in operating temperature, and in some cases, relative
' h) n+ h ^1 D1 M/ uhumidity. The plastics part designer must take a material's response to these conditions ( [) m. N: O2 b
into account. The table below lists the five typical loading and operating conditions, * b- A+ L0 }; d8 L+ i( W
together with the relevant material properties a designer needs to consider.
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1 j& X9 n! v5 VTABLE 1. Typical loading/operating conditions together with the relevant
3 c$ T. q9 Y0 q8 M0 T9 xmaterial properties K5 J7 J" ]3 x" d5 r
Loading/operating conditions. Relevant material properties.
( @2 _+ A7 N8 e. ?: i" E. yShort-term loading. Stress-strain behavior.
: u8 N7 ?; J1 f, r3 P) g( aLong-term loading. Creep and stress relaxation. 9 G) v: F! T& H" _" x) J
Repeated loading. Fatigue. . E5 F: ^' ?+ d! K
High velocity and impact loading. Impact strength. . i2 r" G/ G! T
Loading at extreme temperatures. Thermal mechanical behavior. 9 w; I. U7 U5 K" H1 V
Stress-strain behavior : f8 u4 j1 g$ F8 N E
Part strength
. k. s/ y; | b9 `( IThe stress-strain behavior of a material determines the material contribution to part strength (or / `! X- t5 w! C/ U8 ?/ @3 [
stiffness), the relationship between load and deflection in a plastic part. Other factors that affect part
3 C# S, G& n7 n- r Rstrength include part geometry, loading, constraint conditions on the part, and the residual stresses 5 T4 p5 L' _/ W, Q0 W6 [% i9 a
and orientations that result from the molding process. There are various types of strength, such as ; C/ o0 d* j {4 ~" Z! g$ T5 [1 x7 h/ i
tensile, compressive, torsional, flexural, and shear, depending on the load and restraint conditions
9 ]; k9 H: S; r' x$ Kthe part is subjected to. These types also correspond to the primary load state present in the part. The . j9 G) S, x7 c5 q! x$ i
stress-strain behavior of the material in the same mode as the primary load state in the part is most - |/ J. z, ]9 G; O+ m0 C# n, a$ o/ I
relevant in determining part strength. |
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发表于 2007-5-31 11:12:28