不同应力幅下Ti/SiC $_f$金属基复合材料高温疲劳损伤累积
Damage accumulation during high temperature fatigue of Ti/SiC$_f$ metal matrix composites under different stress amplitudes
摘要：
采用同步加速器X射线计算机断层成像（CT）和X射线衍射（XRD）技术，原位研究了不同应力幅下高强度TC 17钛合金/单向SiC纤维复合材料（纤维直径= 100 $μ$ m）在高温（350 °C）疲劳循环下的损伤机制和载荷重分布。通过CT绘制了裂纹和纤维断裂的三维形态。在稳定生长期间，基体开裂占主导地位，当绕过桥接纤维时，裂纹偏转（高度为50-100 $μ$ m）。少量的桥接纤维断裂接近基体裂纹平面，特别是在相对较高的应力幅循环。加载到峰值应力导致裂纹快速增长，伴随着纤维断裂的爆发。与稳定增长阶段相比，在快速增长阶段，许多纤维断裂发生在距基体裂纹面50-300 $μ$ m处，导致断裂表面上的广泛纤维拔出。在纤维负载，界面应力，和在裂纹附近的纤维-基体脱粘的程度的变化已映射为疲劳循环和快速增长后的高空间分辨率XRD。纤维/基体界面滑动延伸至裂纹平面两侧的600 $μ$ m（在稳定增长区）或700 $μ$ m（在快速增长区）。界面剪切应力的方向与加载周期，与最大摩擦滑动应力达到~55 MPa的稳定增长和快速增长的制度。
英文摘要：
The damage mechanisms and load redistribution of high strength TC17 titanium alloy/unidirectional SiC fibre composite (fibre diameter = 100 $μ$m) under high temperature (350 °C) fatigue cycling have been investigated in situ using synchrotron X-ray computed tomography (CT) and X-ray diffraction (XRD) for high cycle fatigue (HCF) under different stress amplitudes. The three-dimensional morphology of the crack and fibre fractures has been mapped by CT. During stable growth, matrix cracking dominates with the crack deflecting (by 50-100 $μ$m in height) when bypassing bridging fibres. A small number of bridging fibres have fractured close to the matrix crack plane especially under relatively high stress amplitude cycling. Loading to the peak stress led to rapid crack growth accompanied by a burst of fibre fractures. Many of the fibre fractures occurred 50-300 $μ$m from the matrix crack plane during rapid growth, in contrast to that in the stable growth stage, leading to extensive fibre pull-out on the fracture surface. The changes in fibre loading, interfacial stress, and the extent of fibre-matrix debonding in the vicinity of the crack have been mapped for the fatigue cycle and after the rapid growth by high spatial resolution XRD. The fibre/matrix interfacial sliding extends up to 600 $μ$m (in the stable growth zone) or 700 $μ$m (in the rapid growth zone) either side of the crack plane. The direction of interfacial shear stress reverses with the loading cycle, with the maximum frictional sliding stress reaching ~55 MPa in both the stable growth and rapid growth regimes.
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