2-31为了使压力机在最大压力P=160kN时重要机件不发生破坏,在压力机冲头内装有保险器——压塌块,如图所示。保险器材料采用HT20-40铸铁,其极限剪应力?=360MPa。试设计保险器尺寸?。
2-32已知钢板的厚度t=10mm,钢板的剪切强度极限为?b=340MPa,若要用冲床在钢板上冲击直径为d=18mm的圆孔,问需要多大的冲剪力P?
2-33某钢闸门与其吊杆之间是用钢销轴连接的,其构造如图所示。已知闸门与吊杆都是采用3号钢,销轴则采用5号钢;按机械零件计算时,5号钢的许用挤压应力[?jy]=90MPa抗剪许用应力[?]=70MPa,3号钢的许用挤压应力[?jy]=80MPa,试确定此连接中钢销轴的直径d=?
N=68kNP冲头钢板N=68kN单位:题2-32图题2-33图
答案
2-1(a)N 1=20kN,N2=-20kN (b)N1=40kN,N2=0,N3=20kN (c)N1=20kN,N2=-20kN,N3=20kN (d)N1=-20kN,N2=-10kN, N3=10kN 2-3(a)?1=50MPa,?2=-50MPa
(b)?1=100MPa,?2=33.33MPa,?3=25MPa 2-4
时:??=100MPa,??=0 ?=0°
时:??=75MPa,??=43.3MPa ?=30°
时:??=50MPa,??=50MPa ?=45°
时:??=25MPa,??=43.3MPa ?=60°
时:??=0,??=0 ?=90°2-5 ?D?Pl 3EA2-6 (a)?=180MPa
(b)?c=42.5mm (c)P=11.996N 2-7 ?l?bPlln1
Et(b1?b2)b22-8 d=26mm,a=95mm 2-9 d=21.5mm 2-10 AC杆2L80×80×7,CD杆2L75×75×6 2-11
?AB=73.8MPa,安全
?42-12 (1)??5.187?10
(2)??103.8MPa
(3)P=41.52kN
2-13 E金=80.6GN/m2,E银=70.8GN/m2,E钢=199.0GN/m2,E铁=99.45GN/m2,E铅=16.8GN/m2
2-14(2)?=16.6%,?=61.6%
?42-15(1)??5?10,??100MPa,P=7.85kN
(2)???p,不能求出应力 2-16 E=205GN/m2,?=0.317
2-17 P=8.66kN
2-18(1)P=417N,不安全
(2)lmin=1.988m 2-19 P允许=88.6kN
2-20 (1)A1=200mm2,A2=50mm2
(2)A1=267mm2,A2=50mm2 2-21 A1=1384mm2,A2=692mm2 2-22 N1:N2:N3=1:1:1 2-23 (1)x=0.514m
(2)N1=21.4kN,N2=N3=14.3kN 2-24
?CE=96.5MPa,?BD=161MPa
2-25 [P]?2.5[?]A 2-26 e?b(E1?E2)2(E
1?E2)2-27 ?1=-66.6MPa,?2=-33.3MPa 2-28
?t=72MPa
2-29 l=200mm,a=20mm
2-30 ??68.3MPa?[?],?jy?107MPa?[?jy],安全
2-31 ?=2.83mm 2-32 P=192.2kN 2-33 d=42.5mm
max?107MPa?[?],铆接件?