% 定义三个主应力值 sigma1 = 10; sigma2 = 5; sigma3 = 2; % 计算Mises和Tresca的屈服准则 s = (sigma1 - sigma2)^2 + (sigma2 - sigma3)^2 + (sigma3 - sigma1)^2; vm = sqrt(3/2 * s); vt = max(abs(sigma1-sigma2), abs(sigma2-sigma3), abs(sigma3-sigma1)); % 绘制π平面 theta = linspace(0, 2*pi, 100); x = cos(theta); y = sin(theta); plot(x, y, 'k--'); axis equal; hold on; % 绘制Mises屈服轮廓 r = vm/sqrt(2); plot(r*cos(theta), r*sin(theta), 'r', 'LineWidth', 2); % 绘制Tresca屈服轮廓 r = vt/sqrt(2); plot(r*cos(theta), r*sin(theta), 'b', 'LineWidth', 2); % 添加标签 title('Mises and Tresca Yield Contours'); xlabel('\pi_1'); ylabel('\pi_2'); legend('π plane', 'Mises', 'Tresca');这段代码不对，改下

这段代码存在一些问题，主要是变量名错误和计算公式不正确。以下是修改后的代码：

% 定义三个主应力值
sigma1 = 10; 
sigma2 = 5; 
sigma3 = 2;  

% 计算Mises和Tresca的屈服准则
s = ((sigma1 - sigma2)^2 + (sigma2 - sigma3)^2 + (sigma3 - sigma1)^2)/2;
vm = sqrt(3 * s);
vt = max(abs(sigma1-sigma2), abs(sigma2-sigma3), abs(sigma3-sigma1));

% 绘制π平面
theta = linspace(0, 2*pi, 100);
x = cos(theta);
y = sin(theta);
plot(x, y, 'k--'); 
axis equal; 
hold on; 

% 绘制Mises屈服轮廓
r = vm/sqrt(2);
plot(r*cos(theta), r*sin(theta), 'r', 'LineWidth', 2); 

% 绘制Tresca屈服轮廓
r = vt/2;
plot([r, -r, -r, r], [r, r, -r, -r], 'b', 'LineWidth', 2); 

% 添加标签 
title('Mises and Tresca Yield Contours'); 
xlabel('\pi_1'); 
ylabel('\pi_2'); 
legend('π plane', 'Mises', 'Tresca');

其中，Mises屈服准则的计算公式需要除以2，同时Tresca屈服轮廓的绘制需要手动指定四个顶点的坐标。