CAESARII管道应力分析培训(ppt 66页)

2019/8/9
Basic Stress Theory &
基本应力 “Code Stress规范应力”
几个实效理论A Few Failure Theories • 变形能或八面体剪切应力 (根据米赛斯理论和其它的理
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Basic Stress Theory &
Using Mohr’s Circle
• Cut the square at to calculate S1
• Cut the square at +90 to calculate S2
• Cut the square at +45 to calculate max
space • add graphic (rotated cube with loads) • This cube can be rotated so that shear stresses are zero.
This results in the Principal Stresses.
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principal stress is used to set wall thickness • Maximum shear stress is a good prediction and errs on the
conservative side • see p84&85 of Adv. Mech. Of Mat’ls
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Basic Stress Theory &
Using Mohr’s Circle
• Brittle material (failure by fracture) - max principal stress • Ductile material (failure by general yielding) - max
CAESAR II 管道应力分析培训
201wenku.baidu.com/8/9
王大辉 北京艾思弗软件公司
Basic Stress Theory &
www.aecsoft.com.cn
2019/8/9
Basic Stress Theory &
介绍
• 培训的目的在于让您了解和掌握 – 应力分析的基础概念 – 模型和边界条件的建立 – 结果的分析和评判
– 仅说明整体行为 – 无局部作用（表面没有碰撞）
– 忽略二次影响（小转动）
– 遵循胡克定律
2019/8/9
Basic Stress Theory &
Stress Basics应力基础
局部坐标系下管道应力分类（引发应力的载荷）
1. 轴向应力Longitudinal Stress - SL 2. 环向应力Hoop Stress - SH 3. 径向应力Radial Stress - SR 4. 剪切应力Shear Stress -
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Basic Stress Theory &
轴向应力
• 沿管道轴向Along axis of pipe • 轴向力引起Axial Force
– 轴向力/面积 (F/A)
• 内压引起Pressure
– Pd / 4t or P*di / ( do2 - di2 )
• 弯矩引起Bending Moment
very important, its just not part of the “code stress” • 环向应力用来确定壁厚：依据直径、许用应力、腐蚀
裕量、加工偏差、压力确定管道壁厚。
2019/8/9
Basic Stress Theory &
压力引发的径向应力
• 沿半径方向向内 • 内壁的径向应力大小是： -P • 外壁的径向应力大小为 0 • 最大弯曲应力发生在管道的外表面，故该项忽略
2019/8/9
Basic Stress Theory &
剪切应力Shear Stresses
• 平面内垂直半径 • Shear Force剪力
– 在外表面剪力很小，应力计算忽略 – 支架设计有时需要考虑
• Torque扭矩
– 最大应力在外表面 – MT/2Z
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Basic Stress Theory &
• 往复压缩机的分析专题 • 日常遇到的问题和解决方法
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Basic Stress Theory &
介绍
3D梁单元的特征
– 无限细的杆单元 – 全部行为靠端点位
移决定 – 弯曲变形是主要的
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Basic Stress Theory &
介绍
3D Beam Element Characteristics 3D梁单元的特征
Basic Stress Theory &
Simplifying to a 2-D Stress
• Since we use the outside surface where radial stress is zero; let’s move to a plane element:
• This plane can be rotated to either eliminate or maximize shear stress by using Mohr’s Circle:
3-D 应力评定
• A loaded, 3-D pipe contains a representative infinitesimal stress cube
• add graphic (Fig 1-13) • This stress cube is in equilibrium and can be rotated in
2019/8/9
Basic Stress Theory &
基本应力 “Code Stress规范应力”
应力评定Evaluating a 3-D Stress • S = F / A + Pd / 4t + M / Z • 轴向力、轴向压力，轴向弯矩一起的分量加和 • 规范不同，上面的算式也不同 • 那些应力没有包含进来？
– Mc/I – 最大应力环向的外表面某点处 – I/radius Z (截面模量); use M/Z
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Basic Stress Theory &
压力引起的环向应力
• 环向（垂直于半径） • Pd / 2t • 和壁厚紧密相关 • 环向应力十分重要，但规范应力不考虑它。Hoop is