Page 598 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Design and material utilization C HAPTER 18.1

85%
7er 5er 3er
60
80
% of mass HSS 70 40 67%
50
75%
30
20
10
0
E23 E32 E38 E28 E34 E39 E30 E36 E46
60
E46
50
E39
40
30 E38

20
E34
E32
10
E28
E23
E30 E36
0
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Fig. 18.1-19 Possible scenario of future HSS usage. 7

force at increasing levels. Others involve the continued the permanent deformation of the panel is indicated
application of a steadily increasing force until denting since the lower portion of the curve does not return to
occurs. In some cases, stiffness is assessed using the same zero.
basic test equipment but with a much larger radiussed Experimental testing of dynamic dent resistance has
loading head to prevent localized deformation. Force and previously concentrated on drop weight rigs, using vari-
displacement measurements are generally incorporated ous indentor masses and drop heights to achieve a range
into a data acquisition system. of denting energies. Even higher energies can be achieved
An illustration of a typical output from such a test through the use of a compressed air operated ball bearing
would be as represented in Fig. 18.1-20. Initial stiffness is gun. The key issue to be considered is that test conditions
given by the slope of the curve in the first region, until the (denting force, impact speed, etc.) must be genuinely
buckling load is reached. After ‘oil canning’, the panel representative of those conditions existing in field, i.e. if
continues to deflect elasticity, before the onset of plastic the energy input to cause a perceptible dent in-service is
deformation in the material. When the load is reversed, 10 J, then the dent testing procedure should reflect this.

Loading
head
Panel Data acquisition
system
Controllers/
Drive unit
Force D
C
B
A

Displacement
A Initial stiffness B Oil can load C Secondary stiffness D Plastic deformation
Fig. 18.1-20 Test rig for measurement of panel dent resistance and stiffness.

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