Crash energy absorbing part
To provide a crash energy absorbing part which is light in weight, and in which collapsing deformation into a bellows shape occurs more stably even when a crash load is applied in a direction crossing the shock-absorbing direction of the crash energy absorbing part. The crash energy absorbing part of the present invention is constructed of a member that is obtained by forming a sandwich metal sheet ( 1 ), which is formed by laminating a surface layer ( 3 A, 3 B) formed of a metal sheet on each side surface of a core layer ( 5 ) and bonding them. By controlling a deformation rate of a center layer of the sandwich metal sheet ( 1 ) for constructing the crash energy absorbing part, the crash energy absorbing part of the present invention is deformed at a short wavelength regardless of a direction of a crash load that is applied, whereby collapsing deformation into a bellows shape more stably occurs.
1. A crash energy absorbing part configured to absorb crash energy when a crash load is applied to an end portion of the crash energy absorbing part in a shock-absorbing direction,
the crash energy absorbing part is constructed by forming a sandwich metal sheet including surface layers, a core layer, and bonding layers between the surface layers and the core layer, in which each of the surface layers is formed of a metal sheet, and the surface layers are bonded to each surface of the core layer,
wherein the bonding layers comprise an epoxy-based adhesive, an acrylic-based adhesive, or a urethane-based adhesive,
wherein the bonding layers have a shear modulus of not less than 135 MPa and not greater than 500 MPa,
wherein a center layer formed of the core layer and the bonding layers has a deformation rate of not less than 7.0% and not greater than 75.0%,
wherein a shape of a cross section that is perpendicular to the shock-absorbing direction has a curved portion, of which minimum curvature radius is not less than 7.0 mm, at not less than 30.0% of a circumferential length of the cross section, and
wherein the shape of the cross section has a closed structure or has an opening at less than 15.0% of the circumferential length of the cross section, wherein the deformation rate is defined by 100×(Dcal−Dexp)/Dcal
wherein Dcal=Eb(H 3 −h 3 )/12 is the calculated rigidity of the sandwich metal sheet, Dexp is the measured flexural rigidity of the sandwich metal sheet, E is the Young's modulus of the surface layer, b is the width of the sandwich metal sheet, H is the thickness of the sandwich metal sheet, and h is the thickness of the core layer.
2. The crash energy absorbing part according to claim 1 ,
wherein each of the surface layers is formed of a metal sheet which has a Young's modulus that is greater than the Young's modulus of the core layer, and
wherein a thickness ratio t c /t f of the thickness t f of each of the surface layers and the thickness t c of the core layer is not less than 2.0 and not greater than 7.0.
3. The crash energy absorbing part according to claim 1 ,
wherein each of the surface layers is formed of a metal sheet which has a Young's modulus that is greater than the Young's modulus of the core layer, and
wherein a thickness ratio t c /t f of the thickness t f of each of the surface layers and the thickness t c of the core layer is not less than 3.5 and not greater than 5.0.
4. The crash energy absorbing part according to claim 1 ,
wherein a ratio E c /E f of the Young's modulus E f of each of the surface layers and the Young's modulus E c of the core layer is not less than 1×10 −3 and not greater than 1×10 −1 .
5. The crash energy absorbing part according to claim 1 ,
wherein the deformation rate of the center layer is not less than 7.0% and not greater than 50.0%.
6. The crash energy absorbing part according to claim 1 , comprising 4 or more recess portions in a cross section perpendicular to the shock-absorbing direction, each of the recess portions being formed of a curved portion which is formed of a curve having a curvature radius of not less than 7.0 mm and not greater than 15 mm and which is inwardly recessed toward the center of the cross section.
7. The crash energy absorbing part according to claim 1 ,
wherein the surface layer has yield stress of not less than 100 MPa and not greater than 1000 MPa.
8. The crash energy absorbing part according to claim 1 ,
wherein a ratio ρc/ρf of a density ρc of the core layer and a density ρf of each of the surface layers is not less than 1/300 and not greater than ½.