Key Engineering Materials Vols. 385-387

Abstract: A crack propagation criteria is proposed for mixed mode I-II fracture in concrete based on the initial cracking KⅠ-KⅡ curve obtained from experiment. Once the difference between the stress intensity factor at the crack tip caused by the external load and the one caused by the cohesive force attains the above KI-KII curve, the crack begins to propagate. Based on this criteria, the finite element method was used to simulate the mixed mode I-II crack initiation, stable propagation and unstable failure in concrete. For the four-point shear concrete specimens, the crack propagation trajectory and P-CMSD (Crack Mouth Sliding Displacement) curve were obtained. Upon the comparison with the experimental results, the calculated results show good agreement. It is concluded that, if the elastic modulus E, the uniaxial tensile strength ft and the initial cracking KI-KII curve of concrete are measured from experiment, the complete process of mixed mode I-II crack propagation can be simulated using the proposed criterion.

Abstract: This work presents the results of a set of endurance tests performed on steel to steel shaft/bushing tribosystems, without re-lubrication after start-up. The experimental procedure was designed in order to provide simulation for the operative conditions of earthmoving machinery. For this purpose, a new testing machine was specifically manufactured so as to accommodate shaft/bushing assemblies up to a nominal coupling diameter of 90 mm, with a maximum radial load capability of 300 kN. The machine was operated in alternating rotation, with a span angle of 180 degrees, at an angular speed of 10 rpm. The effects of contact pressure intensity were investigated, as well as the effects of grease lubrication type and of the geometry of grease breeding grooves that were located on the bushings inner surface. The tribology behaviour of the tested assemblies was quantified by means of the transmitted torque, grease temperature at the surface of contact and the metallographic analysis of wear out surfaces.

Abstract: This paper describes the experimental results of a set of fatigue tests performed on T300 carbon fiber / epoxy resin laminates cured in autoclave. The effects of anisotropy in laminates lay up have been investigated, as well as the influence of circular hole notches, for both the case of tensile and compressive loading conditions. Due to the high slenderness of specimens, that have the ASTM D3039 standard suggested geometry, a special gripping device has been designed in order to avoid the axial buckling. Fatigue failure probability of the material has been assessed by means of Maximum Likelihood Estimates (MLE) of the experimental data, as a function of the lay-up and load conditions. Eventually, the micrographic analysis of fractured surfaces outlined the combined effects of both the geometry and notches towards the damage behaviour of this kind of material.

Abstract: Our purpose is to propose a methodology for assessing dynamic crack propagation laws under mixed-mode loading. Dynamic brittle fracture experiments are performed on polymethylmethacrylate (PMMA) in which mode combination changes and crack arrest phases occur. Then, these experiments are numerically reproduced by using the eXtended Finite Element Method (X-FEM) in order to validate the algorithms and the criteria assumed.

Abstract: The bolts and nuts are widely used in various fields as important joining elements with long history. However, loosening induced by the vibration and external loads is still a big problem. And the loosening sometimes causes very serious accident without notice. This paper deals with a special stud bolt named “Super Stud Bolt (SSB)” which can prevent loosening effectively. There is a thin walled tube between the upper and lower threads, which can be deformed along the axial direction so that the phase difference is produced and SSB is developed. This phase difference induces the contrary force on the surfaces of the upper and lower threads, which brings out the anti-loosening performance. In this study, the processing and fastening-loosening courses are simulated with the finite element method. And the anti-loosening performance is analyzed and realized. In addition, the anti-loosening performances under various phase differences are compared and finally best dimensions for SSB are examined.

Abstract: The paper presents the compatibility relation of displacement, strain energy expression, and the formulations of Finite Element Method in the transitional region for the improved damage model of 2-D delamination[1]. The postbuckling behaviors of composite laminated plate with a circular delamination are analyzed. Results show that the model mainly improves computational results of energy release rates in the delamination front. The model should only be used in a narrow region near the crack-tip and the normal Mindlin model in other regions. It leads to little increase in the amount of computation, but significant improvement in the results.

Abstract: There could be multi-failure modes in the course of working of the structure system including slender bar members. For example, strength failure, fatigue failure and buckling failure, especially sudden buckling failure would bring large disaster to structure. In this paper, according to Fatigue and Damage Mechanics theory, safe margin expression of the different failure mode of structure (static strength, fatigue and buckling) is given firstly, then by analyzing different failure mode of structural element under static and fatigue loads, and failure mode of the calculating element is confirmed by comparing the failure probability value of different failure mode. In the course of searching for significant failure paths, not only is failure mode that stiffness matrix of structure is zero considered, but also buckling failure mode of compressed residual structure is considered too, so that failure analysis is more reasonable. In the end, the reliability calculating method of the structural system is given, and the validity of the method proposed in this paper is explained combining an example.

Abstract: The problem of failure mode analysis of stochastic structural systems, dealing with the design variables expression, reliability-based structural optimization and improved stability of girders, have been studied in this paper. Considering the material intensity, girder section area, panel thickness and loads as stochastic variables, a mathematical model of optimization is constructed. In the iterative procedure, the optimum vector method was adopted to optimize the object and the gradient step; and the optimum vector step have been used alternatively, and these can speed up the iterative procedure. The calculation of a numerical example shows this method is exact and free from the selection of optimum start point, further more the convergence is stable and fast.

Abstract: Following the Northridge earthquake, widespread damages in connections have been discovered. Then the research on behavior of new beam-column connections has been being a hot spot in recent several years. Non-linear analysis of reduced web connections with circular and rectangular openings in concentrated loading was carried out with finite element method. The parameters were conducted to study the effect of opening ratio, opening style and opening position on bearing capacity. Results show that bearing capacity of reduced web connection reduces with the increase of opening ratio. The opening ratio of reduced web connection takes little effect on bearing capacity when opening ratio is less than 50%. The bearing capacity of reduced web connection with circular opening is larger than rectangular opening if the opening area is equal.

Abstract: Risk analysis can overcome the weakness of conventional safety evaluation of high-arch dams where the random nature of the load and resistance effect are ignored and the failure mode and failure disaster loss are not taken into account. On the basis of statistical analysis of the data of the failure arch dams and faulty and perilous arch dams in the world, it is deduced that the failure of high arch dam is mainly caused by super elevation floods, highly intense earthquakes, mountain landslides, abnormal temperature variation, explosion load, etc. Five major failure modes for high arch dams are suggested, namely dam abutment rock instability, fundamental plane instability, entire entity instability, excess cracking and extreme dam overflow. Based on the study of the failure mechanism of the major failure modes, a state function is established to calculate the failure probability of the major failure modes. An approach is developed to obtain the statistical quantity and the regularities of distribution of the load and resistance random variables.