This command is used to construct an impact material object uniaxialMaterial ImpactMaterial $matTag $K1 $K2 $δy $gap
integer tag identifying material $matTag $K1 $K2 $δy
initial stiffness 初始刚度 secondary stiffness 屈服后刚度 yield displacement 屈服位移
initial gap* 初始间隙 $gap
NOTES:
This material is implemented as a compression-only gap material. Delta_y and gap should be input as negative values. $δy、$gap都为负值。
DESCRIPTION:
This material is based on an approximation to the Hertz contact model proposed by Muthukumar (See REFERENCES below). The energy dissipated during impact is: E = kh * δm^(n+1) * (1-e^2) / (N+1)
where kh is the impact stiffness parameter, with a typical value of EA/L or 25,000 k-in.-3/2; n is typically taken as 3/2 for the exponent associated with the Hertz power rule; e is the coefficient of restitution, with typical values from 0.6-0.8; and δm is the maximum penetration during the pounding event.
n：3/2 ；e：恢复系数，取值：0.6~0.8；δm：最大侵入深度（最大侵入深度为假设值，并不是实际的侵入深度）。
The effective stiffness, Keff, is: Keff = kh * (δm)^0.5 The yield displacement is: δy = a * δm
where a is typically taken as 0.1. The initial stiffness, K1, and secondary stiffness; K2, are then selected such that the Impact model dissipates an amount of energy during a pounding event that is consistent with the associated energy dissipated in the Hertz model. K1 = Keff + E / (a*δm^2) K2 = Keff - E / ((1-a)*δm^2)
Response of Impact Material during a pounding event. Response of Impact Material for displacement cycles of increasing amplitude
你可参考一下文献：
A contact element approach with hystersis damping for the analysis and design of pounding in bridges 以及研究生论文：简支梁斜交梁桥非线性地震反应分析与控制
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