A METHOD FOR PREDICTING BUCKLING LOADS OF COMPOSITE LAMINATED STRIPS WITH A SURFACE NOTCH

Surface notches lower the stiffness of laminated strips, so they lower the buckling loads of the laminated strips, too. In this paper a new method is proposed to predict the buckling loads of the laminated strips with a surface notch. The theoretical and experimental results show that the buckling loads decrease as the depth or width of the surface notches increase; when the stacking sequence of the laminated strips is [0°/0°/+ θ/-θ/0°/0°/+θ/-θ] s , the buckling load decrease as θ increases. It proves that the method is reliable and significant.

某高速公路路基施工与周边房屋开裂关系分析

高速公路施工建设过程中,沿线房屋的开裂原因必须从多角度全方位进行综合分析,才能得出科学合理的结论,正确界定责任。主要从以下几个方面进行分析:所涉区域的地形地质条件及房屋公路位置关系;公路结构形式及施工工艺;房屋开裂特点和发展趋势及变形监测;房屋周围地基及地面变形特征。得出的结论与实际基本吻合,在高速公路建设管理过程中,该项评估方法具有一定参考价值。

Overlying strata movement rules and safety mining technology for the shallow depth seam proximity beneath a room mining goaf

Aiming at the shallow depth seam proximity beneath a room mining goaf, due to that the shallow depth seam is exploited using the longwall mining and overlain by thin bedrock and thick loose sands, many accidents are likely to occur, including roof structure instability, roof step subsidence, damages of shield supports, and the face bumps triggered by the large area roof weighting, resulting in serious threats to the safety of underground miners and equipment. This paper analyses the overlying strata movement rules for the shallow seams using the physical simulation, the 3DEC numerical simulation and the field mea- surements. The results show that, in shallow seam mining, the overburden movement forms caved zone and fractured zone, the cracks develop continuously and reach the surface with the face advancing, and the development of surface cracks generally goes through four stages. With the application of loose blast- ing of residual pillars, reasonable mining height, and roof support and management, the safe, efficient and high recovery rate mining has been achieved in the shallow depth seam proximity beneath a room min ing goal.

Fracture of thermal barrier coating with multiple surface cracks and delaminations:Interlayer effect

Multiple surface cracks and interfacial delamination are the major failure mechanisms in film/substrate systems.The effect of interlayer upon the failure mechanisms of interfacial delamination concomitant to surface crack was explored.Finite element model was developed to obtain the stress and energy release rate(ERR),which governs the propagation of interface cracks.The dependences of delamination upon the geometry and constitutive properties of interlayer were examined.The results indicate that the effect of elastic modulus of interlayer on the steady state ERR is insignificant.In cases of different geometrical parameters,however,the steady ERR decreases with the increase of the interlayer thickness.These findings lead to the conclusion that the interlayer constraint has significant effect on the ERR and thus coating life,which can be adopted to modify the ceramic top coat.

聚苯颗粒砂浆外墙外保温施工存在的问题及对策

聚苯颗粒砂浆外墙外保温系统是出现的又一种外墙外保温体系,该材料施工简单快捷,环保节能,有着很好的保温效果。但在实际的应用过程中,由于建筑物结构形式、系统材料、施工工艺等方面的原因,会造成渗水、脱落,丧失节能效果,缩短建筑物使用寿命,甚至会危及墙体的安全。文章主要针对聚苯颗粒砂浆外墙外保温施工容易出现的质量问题,并提出防治措施与对策。

The interfacial fracture behavior of foam core composite sandwich structures by a viscoelastic cohesive model

A sandwich beam model consisting of two face sheets and a foam core bonded by a viscoelastic adhesive layer is considered in order to investigate interfacial fracture behavior. Firstly, a cohesive zone model in conjunction with a Maxwell element in parallel, or with a Kelvin element in series, respectively, is employed to describe the characteristics of viscoelasticity for the adhesive layer. The models can be implemented into the implicit finite element code. Next, the parametric study shows that the in- fluences of loading rates on the cohesive zone energy and strength are quite different for different models. Finally, a sandwich double cantilever beam model is adopted to simulate the interface crack growth between the face sheet and core. Numerical examples are presented for various loading rates to demonstrate the efficacy of the rate-dependent cohesive models.

Experimental study on the interfacial delamination in a thermal barrier coating system at elevated temperatures

The failure mode and adhesion of thermal barrier coating (TBC) 8YSZ (ZrO2+8% (w/w) Y2O3) deposited on NiCoCrAlTaY bond coat by atmospheric plasma spraying were investigated. A grooved modified three-point bending specimen that can generate a single interface crack to facilitate the control of crack growth was adopted for testing, which was conducted at the ambient temperature of 100 °C. The morphology and composition of fractured surfaces were examined by means of a scanning electron microscopy (SEM) and an energy disperse spectroscopy (EDS). Images and spectrum show that cracks are initiated and propagated exclusively within YSZ layer adjacent to top/bond coat interface. The load-displacement curves obtained exhibit similar shapes that indicate two distinct stages in crack initiation and stable crack growth. Finite element analyses were performed to extract the adhesion strength of the TBCs. The delamination toughness of the plasma-sprayed 8YSZ coatings at 100 °C, in terms of critical strain energy release rate Gc, can be reliably obtained from an analytical solution.