Primary stress/secondary stress 分类问题

sinozsq

ASME BPVC VIII-2 part 5(5.2.2.12  Stress Categorization) 讲到
   *Primary stress,P;
   *secondary stress,Q;
   *Peak stress, F
哪位大虾来说说理解心得？有没有受力的图形实例上传大家看看？

sinozsq

拿ASME的定义抛砖引玉下：
*Primary stress  P   ： is not self-limiting, and failure, or at least gross distortion, can occur from one application of the loading. Primary stress is stress caused by the application of mechanical pressure, forces and moments. Thermal stresses are not primary stresses. Primary stress includes both membrane and bending stress and is linearly distributed across the wall section.

*Secondary stress Q:    is caused by the constraint of adjacent parts or by self-constraint of the structure, and yielding can cause the source of the stress to be eliminated. One load cycle can cause local yielding and stress redistribution but cannot result in failure or gross distortion. Secondary stresses are membrane plus bending stresses that can occur at gross structural discontinuities, from general thermal stress, from mechanical preload conditions, or from combinations of these sources.

*Peak stress, F :           is the increment of stress added by a stress concentration or other source that does not cause noticeable distortion. Such sources include thermal stress in a cladding material with a different coefficient of expansion from the base material; by transient thermal stress, or by the non-linear portion of a thermal stress distribution. The only concern with peak stress is that it may cause the initiation of a fatigue crack or brittle fracture.

NAFEMS给出进一步解释：

Primary stress is related to mechanical loading directly and satisfies force and moment equilibrium. Primary stress that exceeds the yield stress by some margin will result in failure. By contrast, secondary stresses are those arising from geometric discontinuities or stress concentrations. For an increasing external load, at any point, both primary and secondary stresses increase in proportion to this load, until the yield point is reached. But secondary stresses are termed self-limiting by the ASME code: that is, once the yield point has been passed locally around the stress concentration, the direct relationship between load and stress is broken, due to the reduced post-yield stiffness of the material. This is in contrast to primaries (sometimes termed ‘load controlled’ stresses) that will continue to increase in overall magnitude, in direct proportion to the applied load, irrespective of the shape of the stress-strain curve, until failure.

In a region away from any discontinuities, only primary stress will arise. The secondary stress cannot arise alone however - at a discontinuity, the secondary stress will be superimposed on the underlying primary stress.

供大家参考。

阿谢克那·李

Primary stresssecondary stress 分类问题

yuwen

谢谢二楼的分享                       

anjb1234

楼主说发非常好，受教了。

sinozsq

没有人来谈谈心得么？

sinozsq

阿谢克那·李 发表于 2015-9-4 22:18
Primary stresssecondary stress 分类问题

阿谢克那·李大虾有神么看法么？

inconel

You do not get detailed background information from ASME codes. Pressure vessel design books would solve this problem

•        Principal stress aka Direct stress aka Tensile stress or compressive stress
•        Shear Stress ---- It is similar to direct stress (Some authors consider shear stress also comes under principal stress)
•        Secondary Stresses are bending stress, torsional stress, thermal stress
•        Combination stress are the combination any possible stress combination available in principle stress and secondary stress.

Primary Stresses are,
•        General membrane stress (Pm)
•        Local Membrane Stress (PL)
•        Bending Stress (Pb)

Secondary Stresses are,
•        Secondary membrane stress (Qm)
•        Secondary bending stress (Qb)

Peak Stress
•        Peak stress (Pf) is the additional stress intensification in localised areas.


For more details, pls refer Pressure Vessel Design by Dennis R Moss, Chapter-1.
Of course, many other authors books are also available for pressure vessel design and for stress analysis.

inconel

You do not get detailed background information from ASME codes. Pressure vessel design books would solve this problem

•        Principal stress aka Direct stress aka Tensile stress or compressive stress
•        Shear Stress ---- It is similar to direct stress (Some authors consider shear stress also comes under principal stress)
•        Secondary Stresses are bending stress, torsional stress, thermal stress
•        Combination stress are the combination any possible stress combination available in principle stress and secondary stress.

Primary Stresses are,
•        General membrane stress (Pm)
•        Local Membrane Stress (PL)
•        Bending Stress (Pb)

Secondary Stresses are,
•        Secondary membrane stress (Qm)
•        Secondary bending stress (Qb)

Peak Stress
•        Peak stress (Pf) is the additional stress intensification in localised areas.


For more details, pls refer Pressure Vessel Design by Dennis R Moss, Chapter-1.
Of course, many other authors books are also available for pressure vessel design and for stress analysis.

wtf119911

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