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首页> 外文会议>Proceedings of the American Society for Composites Twenty-Ninth technical conference, Proceedings of the 16th US-JAPAN conference on composite materials ASTM-D30 meeting >The Inclusion of Arbitrary Load Histories in the Strength Decay Model for Stress Rupture
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The Inclusion of Arbitrary Load Histories in the Strength Decay Model for Stress Rupture

机译：应力破裂强度衰减模型中包含任意载荷历史

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Stress rupture is a failure mechanism where failures can occur after a period ofrntime, even though the material has seen no increase in load. Carbon/epoxy compositernmaterials have demonstrated the stress rupture failure mechanism. In a previous work,rna model was proposed for stress rupture of composite overwrap pressure vesselsrn(COPVs) and similar composite structures based on strength degradation. However,rnthe original model was limited to constant load periods (holds) at constant load. Thernmodel was expanded in this paper to address arbitrary loading histories andrnspecifically the inclusions of ramp loadings up to holds and back down. Thernbroadening of the model allows for failures on loading to be treated as any otherrnfailure that may occur during testing instead of having to be treated as a special case.rnThe inclusion of ramps can also influence the length of the “safe period” followingrnproof loading that was previously predicted by the model. No stress rupture failuresrnare predicted in a safe period because time is required for strength to decay fromrnabove the proof level to the lower level of loading. Although the model can predictrnfailures during the ramp periods, no closed-form solution for the failure times could bernderived. Therefore, two suggested solution techniques were proposed. Finally, thernmodel was used to design an experiment that could detect the difference between thernstrength decay model and a commonly used model for stress rupture. Although theserntypes of models are necessary to help guide experiments for stress rupture, onlyrnexperimental evidence will determine how well the model may predict actual materialrnresponse. If the model can be shown to be accurate, current proof loadingrnrequirements may result in predicted safe periods as long as 10~(13) years. COPVsrndesign requirements for stress rupture may then be relaxed, allowing more efficientrndesigns, while still maintaining an acceptable level of safety.
机译：应力破裂是一种失效机制，即使材料负荷没有增加，也可能在一段时间后发生失效。碳/环氧树脂复合材料已经证明了应力断裂破坏机理。在先前的工作中，提出了基于强度退化的复合材料外包装压力容器rn（COPVs）和类似复合结构应力破坏的rna模型。但是，原始模型仅限于恒定载荷下的恒定载荷周期（保持）。本文对模型进行了扩展，以处理任意的载荷历史，特别是包含上升到保持和下降的斜坡载荷。模型的扩展使得可以将加载失败视为在测试过程中可能发生的任何其他失效，而不必将其视为特殊情况。rn包含坡道还可能会影响安全加载之后的“安全期”的长度。先前由模型预测。在一个安全的时期内，不会预测到任何应力破裂故障，因为从强度到屈服强度下降到较低的载荷水平需要一定的时间。尽管该模型可以预测斜坡期间的故障，但无法得出故障时间的封闭式解。因此，提出了两种建议的解决方法。最后，使用模型来设计实验，以检测强度衰减模型与常用的应力破裂模型之间的差异。尽管模型的类型对于帮助指导应力破裂实验是必要的，但是只有实验证据才能确定模型对实际材料响应的预测程度。如果可以证明模型是正确的，则当前的证明载荷要求可能会导致预测的安全期长达10〜（13）年。然后可以放宽对应力断裂的COPV设计要求，从而在保持可接受的安全水平的同时，进行更有效的设计。

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