查看更多>>摘要：As more aircrafts reach or exceed their design life, it is becoming very important to research multiple cracks damage, especially the multiple site damage (MSD) in order to re-evaluate their service life and damage tolerance/durability performance. The existing of MSD may remarkably reduce the residual strength of an aerospace structural component than those with a singe lead crack. This study investigated the residual strength of aluminum alloy sheet with MSD through three types of aluminum specimens test. Aluminum panels with bare collinear constant diameter holes were chosen as specimens. After some constant amplitude tension-tension load cycles, the MSD were found in these specimens since there were multiple fatigue cracks emanating from the saw cuts of holes. The residual strength was recorded as the maximum load when every specimen was subjected to monotonically increasing tensile load until failure occurred. In different failure prediction criteria that were often used in engineering in order to evaluate the accuracy of these criteria, Swift criterion (ligament yield) criterion got more accurate prediction results than other criteria. Although Swift criterion was more accurate than some other criteria, its error was still big for some specimens. Two modified approaches were proposed in order to get more accurate and appropriate failure criterion for MSD structure.
查看更多>>摘要：An three-dimensional FE model of threaded connection is proposed by means of the general purpose program ANSYS. The model is accurately constructed according to the helical thread profiles. The mechanical behavior of each bolt subjected to eccentrically loading is investigated and the stress distribution is discussed detailedly. Based on the stress level, the fatigue life of threaded connection is predicted by the cumulative damage method. This work can provide a deeply understanding on the mechanics behavior of bolt connection in engineering, especially for its application on the appending equipments of airplane.
查看更多>>摘要：A great earthquake of magnitude 8.0 occurred on May 12, 2008 (Beijing Time) in Wenchuan, Sichuan Province of China. Leigu town, which adjoins Beichuan county, was the most seriously damaged place in this earthquake. The teaching buildings were destroyed severely and the earthquake disaster phenomena is very typical. In this paper, firstly, the characteristics of structures and the earthquake damage of the teaching buildings in Leigu town are introduced in detail. Secondly, their damage states are calculated by means of structure vulnerability analysis, which are used for comparative analysis with actual damage states, and the influencing factors on seismic behavior are analyzed. Finally, some reasonable suggestions on the reconstruction of teaching buildings after disaster have been given.
查看更多>>摘要：Investigation on mechanical properties of rock, soil and powder metallurgy is an important subject in study of damage constitutive models. These materials contain micro-voids (such as defects, inclusions and cracks) and perform pressure sensitivity. Unlike metal materials, hydrostatic pressure can influence plastic yield of these materials. Following the modified Gurson model in meso-mechanics and considering the meso-compressibility, this paper focuses on plastic limit analysis of micro-deformation mechanism of these materials. The two-independent-parameters criterion is taken as matrix yield function and spherical voids as the represent unit cell. The macroscopic stress and strain rate related to micro structure parameters are derived via upper-bound theorem. Then the macroscopic yield function (containing micro structure parameters) is established. Finally, the properties of macroscopic yield surfaces are studied by setting different values of these micro parameters. This paper provides theory foundations for materials damage and design.
查看更多>>摘要：In this paper, the mechanical properties of ice, which are affected by the existence of cavities and the different tensile-compression strength ratio, are analyzed in micromechanics view. Then the constitutive equation is established, and the distribution of stress field caused by the ice-structure interaction is constructed with the constitutive equation. Finally, the ultimate bearing capacity of ice is also discussed with different values of pressure sensitivity parameter and the tension-compression ratio. Thus, this paper provides the theoretical reference for offshore platforms design.
查看更多>>摘要：It is well known that shot peening has a marked benefit on fatigue life for the majority of applications. This effect is attributed mainly due to the compressive residual stress state at the component's surface due to shot peening. The present paper evaluates the ability of several fatigue life prediction models, commonly used for general analyses, to predict the behaviour of components with compressive residual stress due to shot peening. Advanced elastic-plastic finite element analyses were carried out in order to obtain stress, strain, strain energy and fracture mechanics parameters for cracks within a compressive residual stress field. With these results several total fatigue life prediction models (including critical distance methods) and fracture mechanics based models were applied in order to predict fatigue life. Fatigue life predictions were compared with several experimental fatigue tests carried out on specimens, representative of a critical region of a compressor disc in a gas turbine aero engine. The results obtained showed that total fatigue life methods, even if combined with critical distance methods, give conservative results when shot peening is considered. Fatigue life was successfully predicted using the method proposed by Cameron and Smith, by adding initiation life to crack propagation life. This last method was also successfully applied for the prediction of non-propagating cracks that were observed during the experimental tests.
查看更多>>摘要：In this paper, the method of continuum damage mechanics is used to construct the damage constitutive equations for the material, and governing equations are obtained based on the assumption of spherical symmetry. Then the stress value is taken as basic unknown parameter to solve these equations, the distribution of materials damage field was also obtained. Finally, the influence of different damage parameters on average distribution is discussed. Thus the paper lays a necessary foundation for research on materials damage evolution law.
查看更多>>摘要：The safety of aged steel structures, especially those with cracking members, has aroused a great deal of attention. In this paper, the application of fracture mechanics for evaluating the ultimate load-carrying of steel material is proposed. Three-point bending tests of three specimens with the mode-I fracture are done to get the ultimate load-carrying capacity, when specimens are destroyed. Fracture ductility KIC, and the steel allowable stress [σ] with certain crack length are formulated. Magnetic method for measuring cracks of steel members is adopted for an aged steel truss bridge, and material composition of specimens is tested, and field nondestructive load test involved static and dynamic test are carried into execution. By comparing the results of the calculation and those of the field test, some conclusions are obtained, which are likely to contribute to safety evaluation of aged steel structures, or contribute to designing similar bridges.
查看更多>>摘要：In this paper, the concepts of preventive maintenance are presented in first part, and second part of the paper present several mathematical models for prediction service life as a base for preventive maintenance forecasting. These models aid in determining the frequency of inspections that will allow the condition of a piece of equipment to be determined in order to plan an appropriate maintenance action.The problem of determination of the service life is directly related to geometry, multiaxial loadings, materials and appropriate models for prediction of the failure propagation. The more precise modelling of these input parameters the more precise and reliable the results are. Therefore in the paper we will present models and procedures for calculations service life, remain service life and/or service control cycle.
查看更多>>摘要：The fracture properties of the thermo-setting materials of epoxy asphalt mixture were evaluated based on J-integral concept and ultimate strength and compared to that of HMA with thermo-plastic binder materials. Totally 60 specimens cored from SGC with different notches were tested with SCB test under a temperature of -10℃ and 20℃. The experimental results reveals that epoxy asphalt mixture has a super higher resistance of fracture at low temperature than thermo-plastic HMA due to its super high tensile strength and flexibility, and the influences of temperature on the fracture resistance of EAM is not so significant as that of thermo-plastic HMA. Good repeatability of SCB test results indicates the capability of the SCB test to be useful for measuring the fracture toughness of epoxy asphalt mixture.
NETL
NSTL