高强混凝土剪摩试验

介绍50组未开裂、预开裂和有施工缝的高强混凝土试件的剪摩试验。试验给出了一个可以更精确地预测有着施工缝及未开裂表面的高强混凝土剪摩强度的公式,并建议现行的剪应力上限0.2fc′应予以保留,而5.5MPa的剪应力限制应予以取消。试验表明,现行ACI规范中有关剪摩的规定同样适用于高强混凝土,但有些保守。

Mechanical properties,corrosion behavior and biocompatibility of orthopedic pure titanium−magnesium alloy screw prepared by friction welding

The dissimilar joining of biodegradable magnesium alloy to pure commercial titanium by rotational friction welding with rotational speeds of 1100,1200 and 1300 r/min for the production of bio-screw was investigated.The metallographic analysis revealed that a good joining was obtained at the Ti/Mg alloy joint.On the magnesium alloy side,various regions such as the weld center zone(WCZ),dynamic recrystallization zone(DRX),thermo-mechanically affected zone(TMAZ)and partially deformed zone(PDZ)were observed.The highest tensile and shear strengths were 173 and 103.2 MPa,respectively at a rotational speed of 1300 r/min.The Ti/Mg alloy dissimilar friction welded joint failed at the vicinity of the intermetallic zone containing Ti3Al phase.The hardness values from the base metal magnesium alloy to the joining point increased mainly due to grain refinement(8.57μm in diameter)and the presence of titanium particles,while the hardness values were constant on the titanium side.It was also found that the corrosion rate of the Ti/Mg alloy joint was higher compared with that of the Ti and Mg alloy from the immersion studies.Additionally,the sample with a rotational speed of 1300 r/min showed better biocompatibility and a cell viability of 98.12%due to better corrosion resistance.

Comparison of microstructure and mechanical properties of conventional and refilled friction stir spot welds in AA6061-T6 using filler plate

Friction stir spot welding with refilling by friction forming process （FSSW-FFP） was successfully modified using filler plate. Both of this new refilling technique and conventional friction stir spot welding （FSSW） process were used to weld A1 6061-T6 lap shear specimens and the results were compared. Effects of tool rotational speeds on mechanical and metallurgical properties in both the cases were studied. Static shear strength of refilled weld samples was found to be better than those welded by conventional FSSW process at all tool rotational speeds. This is explained in terms of effective increase in cross-sectional area of weld nugget due to addition of more material from filler plate, thereby eliminating the probe hole. Failure mechanisms were discussed and fracture surfaces were analyzed through scanning electron microscopy （SEM）. The hardness profile of the welds exhibited a W-shaped appearance in both the processes and the minimum hardness was measured in the HAZ.

Granular dynamic shear strength and its influencing factors

The granular dynamic shear strength is the same as that of the static one in nature, as found from numerous experiments and investigations. The shear strength is equal to the sum of the internal frictional force and the cohesive force. The influences of type, shape, size distribution, pore ratio, moisture content and variation of vibration velocity on the dynamic shear strength of granules were studied. Based on numerous vibration shear experiments, the authors investigate the mechanism of dynamic shear strength in granules in terms of the fundamental principle and the relevant theory of modern tribology.

侧向预压增量法解析土压力

随着基坑分层挖深,在侧壁土体自重作用下,土楔体滑移斜面会处于主动极限平衡状态(向下滑移)。在此状态下由锚杆或支顶对侧壁施加的预压力传至土楔体滑移面上,在土粒间产生的压应力、剪应力、摩阻抗剪强度增量能平衡阻止斜面向下滑动。当继续挖深可使其再处于上述状态。基于这一概念结合莫尔作用应力及库仑强度理论推证导出:抗剪应力强度增量与主应力增量之间函数式,再归并导得:大小主压应力增量相关公式。给出基坑挖深土楔体内应力分布图,建立侧向预压力与基坑顶面竖向荷载作用下基坑侧壁直立深度解析公式,它可适用于土工试验广义折线性强度理论,并绘以应力圆剪切包线几何图式,给出非线性内力分析方法。与当前土压力作用模式对比可明显增加基坑挖深。