The entire beam hinging collapse mode is the most desirable collapse mode. The story collapse of the structure, especially the structure including brittle failure columns, is most undesirable. The system reliability is concerned with the failure element performance. Then the structural reliability with the ductile failure elements can be analyzed using the last hinging collapse mode, but the structural reliability with the brittle failure elements should be analyzed by the step-by-step method. In this paper, the story collapse reliability of the structure with brittle failure elements is investigated and the element safety margin of brittle failure elements is proposed to be βMQ = 1.5 for column ductile failure.
This paper presents a probabilistic approach to evaluating the geotechnical stability problem by incorporating the stochastic spatial variability of soil strength within the numerical limit analyses. The undrained shear strength is treated as a random field which is characterized by a log-normal distribution and a spatial correlation length (i.e., isotropic correlation structure). The current calculations use a Cholesky Decomposition technique to incorporate these random properties in numerical limit analyses. The Random Field Numerical Limit Analyses are applied to evaluate the effect of spatial variability of soil strength on the slope stability and the failure mechanism. Monte Carlo simulations are then used to interpret the failure probability of slope for selected ranges of the coefficient of variation in undrained shear strength and the ratio of correlation length to slope height. The results show how the failure probability of slope is related to the average strength, the coefficient of variation and correlation length scale in the shear strength of slope. Based on the result, the conventional safety factor of slope stability is evaluated to obtain a target probability of failure.
This paper presents a time-dependent fracture model for strength properties estimation of porous ceramics under various load modes. Unified time-dependent fracture model for reliability analysis of strength properties was established on the basis of thermally activated process concept in conjunction with two-parameter Weibull distribution. Fracture strength data obtained under various load modes tests using specimen having different shape or size, can be estimated commonly the aid of the model if the fracture mechanism is all same under various load modes. The model was applied to strength data of porous ceramics obtained from quasi-static bending test and cycle fatigue test. All the data could be estimated commonly.
A new method for materials selection in reliability-based design was applied to the high temperature structural components under creep-fatigue damage mode. The creep-fatigue interaction law was formulated in terms of creep time fraction (creep damage) and fatigue cycle fraction (fatigue damage) using pure creep and pure fatigue material properties referring NIMS creep and fatigue datasheets for ferritic heat resistant steels such as 1Cr-1Mo-0.25V steel forging, 12Cr-1Mo-1W-0.3V steel bar and 2.25Cr-1Mo steel plate. The statistical distribution under the creep-fatigue damage mode was fitted well with the two-dimensional log-normal distribution function but the scatter bands of creep-fatigue data were considerably larger compared with the cases using pure creep and pure fatigue damage distributions. Once the ratio of creep damage to fatigue damage was fixed, the confidence limit could be restricted within more reasonable range for design application. The diagram was expressed by the relationship between creep stress vs. fatigue strain range for those three materials and the apparent superiority of 12Cr-1Mo-1W-0.3V steel bar to other materials was demonstrated. Thus this diagram was proved to be an effective tool for decision making of materials selection and structural reliability-based design even at the very initial stage of design process, that is, the front-loading design of components.
In recent years, a considerable amount of discussion has taken place about the environmental problems on a worldwide scale. Environmental load gases, such as CO2, SOx, and NOx, are generated in the manufacturing process of metal materials, which cause environmental destruction. Thus, the generation of environmental load gases in the process of manufacturing various heat-resistant materials was estimated using an environmental load calculation system developed by Halada et al., and the indicator of the optimum material selection is discussed from the viewpoint of environmental conformity. Research was conducted with regard to the relationship between the environmental load gases of heat-resistant materials, and mechanical properties at high temperature were also investigated. Consequently, it was understood for the heat-resistant materials with many kinds of additional alloy element that there are generating considerable amount of the environmental Consequently, it was understood that heat-resistant materials with many kinds of additional alloy elements generate a considerable amount of environmental load gases during the manufacturing process. Moreover, the guidelines for material selection were established for the design of an apparatus used at high temperature on the basis of the optimal environmental conformity.
In recent years, the laminated materials are designed and used widely in aerospace applications, for example. Therefore, it is important to evaluate the fracture characteristic of the laminated materials. In this research, the basic study on damage tolerant design for the laminated materials subjected to impact load is systematized. The dynamic fracture behavior is analyzed by using the high-speed video camera and the digital image correlation method or caustics method. The dynamic stress intensity factor is experimentally calculated with both the digital image correlation method and caustics method. These two kinds of analysis results are compared, and the reliability of the analytical method in the digital image correlation method is confirmed. In addition, the mixed-mode ratio, dynamic fracture toughness and kinking angle are evaluated from the dynamic stress intensity factor for the control and forecast of fracture. And, the characteristic of mixed-mode fracture criterion showing the condition and the behavior of fracture is examined. It is shown to be able to properly act as damage tolerant design by the materials evaluation method.
After the great Hanshin-Awaji Earthquake, we started the discussion about the combination of measures on earthquake. For example, one is to strengthen the design specification with earthquake. The other is how to evacuate after the occurrence of earthquake. In this study, we try to consider the combination of two required functions by the idea of multi state system (MSS). And we define the reliability of evacuation. Completed evacuation time is calculated by simulation. The reliability of evacuation is shown by the probability that completed evacuation time becomes shorter than required evacuation time. Then, we define the reliability estimation matrix using required evacuation time, number of sign, number of evacuation and so on.
For the reliability design of mechanical structures under cyclic loading, S-N properties of the material are essential as the fundamental reference data. From this viewpoint, the Committee on Standardization of Fatigue Reliability Evaluation of Metallic Materials in JSMS has published the “Standard Evaluation Method of Fatigue Reliability for Metallic Materials -Standard Regression Method of S-N Curve-”. In recent years, this standard is applied to various series of industrial materials in the “Database on Fatigue Strength of Metallic Materials” to investigate the fundamental fatigue properties. In this paper, high strength steel is selected as the target material and the rotating bending fatigue test data for JIS-SCM435, SCM440 and SNCM439 were extracted from the Database. Applying the JSMS standard (JSMS-SD-6-04), S-N curves were analyzed on the basis of 8 types of regression models accepted in the standard. From numerical results, it is confirmed that there are distinct correlation between (1) tensile strength of sB and fatigue limit, (2) slope and intercept of inclined part of S-N curve, (3) slope and the critical number of stress cycles giving fatigue limit. It was also found that S-N property of the individual material was well normalized by tensile strength of sB. Based on this aspect, a number of fatigue data extracted were pooled altogether and P-S-N property was also analyzed. As a result, the change of distribution pattern is observed at low stress level. This aspect is considered to be caused by the change of failure mode in this region.
In the present paper, the impact responses and overall damages of Fibre-Metal Laminates based on titanium alloys and glass fibre-reinforced polymers (Ti/GFRP) as Ti/FRP laminate system were evaluated. Low-velocity impact tests using a drop-weight tower were conducted for the cross-plied GFRP laminates and the Ti/GFRP laminates, and the impact responses during impact loading were obtained. Impact damages such as cracks in titanium layer and delamination of titanium-GFRP interface or matrix cracks and interlaminar delamination in GFRP layer were observed from the impact direction. From the experimental evidence, it was found that the Ti/GFRP laminates showed same impact damage modes as of other types of Fibre-Metal Laminates. Internal damages in the Ti/GFRP laminates were restrained by the reinforcing effect of titanium and adhesive layer compared to the cross-plied GFRP laminates. The Ti/GFRP laminates showed two patterns of the impact responses and damages with the threshold impact energy of about 4.8J. With higher impact energy than this threshold, single crack was presented in titanium layer at non-impacted side. The interlaminar delamination area in GFRP layer increased sharply due to the occurrence of this crack. Numerical analysis model that represent the impact behaviour of the Ti/GFRP laminates using finite element method was suggested based on the damage observations. The impact responses obtained by the dynamic analyses agreed well with the experimental results. The calculated area of interlaminar delamination in GFRP layer as a function of impact energy showed same behaviour as seen in the experiments. As a consequence, it was shown by the analysis as well that the drastic increase in the internal damage area of the Ti/GFRP laminates was induced by the fracture in outer titanium layer under the out-of-plane impact loading.
This study proposes a real-time monitoring method for degree of cure (DOC) of curing resin by refractive index measurement using a single-mode optical fiber based on the Fresnel reflection at the fiber end. First, we particularly present an approach for measuring refractive index of resin in real time without the effects of unexpected backward reflection. We applied this approach to measurement of refractive index of an epoxy resin during cure process, and experimentally confirmed that the change of the refractive index was stably measured in real time. Next, we proposes a new approach to calculate DOC from change of refractive index by eliminating effect of temperature change on refractive index of curing resin. This approach can quantitatively evaluate the DOC in real time, which is not obtained by conventional methods, and provide information in the small region at the fiber end. The experimental results of monitoring cure process of the epoxy resin showed that the DOC could be stably measured by this approach without effect of the temperature change. Furthermore, the DOC obtained by this approach was compared with the DOC curve by the thermal analysis using differential scanning calorimeter. These experiments revealed that the DOC by the present approach represented the curing condition of the resin regardless of the cure pattern and was easily translated into the DOC by the thermal analysis. The present approach of real-time quantitative evaluation of the DOC can be applied to fast cure reaction as well as slow reaction demonstrated in this paper.