双线性弹塑性模型(四)
2021年6月21日 浏览:2239 评论:1 收藏:4
本节内容为在牛顿-拉夫逊方法中集成基于随动硬化模型的当前应力计算。
对于非线性的问题,一般将其线性化为
一次迭代得到的是位移增量,如图所示
接下来要将位移增量转化为应变增量,以一维杆结构为例,其应变增量
其中 为杆初始长度。
[算例]
一根各向同性杆,一端固定,另一端施加轴向力做拉伸试验.荷载逐渐增加到 ,然后逐渐卸载至0。, 。
import math
def Sgn(x):
if x > 0 :
return 1
elif x < 0 :
return -1
else :
return 0
def KinematicHard1D(MP,deps, stressN,alphaN, epsN):
E = MP[0]
H = MP[1]
Y0 = MP[2]
stress_tr = stressN + E*deps
eta_tr = stress_tr - alphaN
f_tr = math.fabs(eta_tr ) - Y0
if f_tr < 0:
stress = stress_tr
alpha = alphaN
ep = epsN
flag = 0 # 处于弹性状态
else:
dep = f_tr / ( E + H )
stress = stress_tr - Sgn(eta_tr) * E * dep
alpha = alphaN + Sgn(eta_tr) * H * dep
ep = epsN + dep
flag = 1 # 处于塑性状态
return stress, alpha, ep, flag
######### 以上为harden模块
import matplotlib.pyplot as plt
import numpy as np
import numpy as np
import harden
E = 70000; H = 10000; sYield = 250
Et = E*H / (E+H)
mp = [E, H, sYield]
nS = 0
nep = 0
nA = 0
A = 100
L = 1000
tol = 1.0E-1
u = 0
Res = 0
nincr = 0
max_iter = 20
epnew = 0
Load = [0,5000, 10000, 15000,20000,25000,30000,25000,20000,
15000,10000,5000,0 ]
N = len(Load)
flag = 0
X = np.zeros( (N) )
Y = np.zeros( (N) )
for i in range(N):
nincr += 1
print('第{}增量步:' .format(nincr) )
P = Load[i]
Res = P - nS * A
du = 0
niter = 0
conv = 2e12
print('迭代步 位移 不平衡力 收敛参数')
while ( conv > tol and niter < max_iter ):
niter += 1
Eep = E
if flag == 1:
Eep = Et
K = Eep*A/L
delta_u = Res / K
du = du + delta_u
delta_eps = delta_u / L
Snew, Anew, epnew, flag = harden.KinematicHard1D(mp,delta_eps,nS,nA,nep)
Res = P - Snew*A
conv = Res**2 / (1 + P**2)
nS = Snew
nep = epnew
nA = Anew
print(format(niter, '>3d'), format(u, '>20.12f'), format(nS, '>26.14f'), format(conv, '>28.16e'))
u = u + du
X[i] = u
Y[i] = nS
print(X)
print(Y)
fig, axs = plt.subplots(1, 1, figsize=(8,6) )
axs.plot(X, Y, label="M1", linewidth = 3, color = "deeppink",marker='o', markersize=12)
axs.set_xlabel('$Displacement(mm)$', fontsize = 18)
axs.set_ylabel('$Stress(MPa)$', fontsize = 18)
fig.savefig('./f358.png', dpi = 300) #保存图片
plt.show()
得到的迭代路径
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