Dominant failure mode analysis using representative samples obtained by multiple response surfaces method

Different failure modes occur in textile‐reinforced composite under applied loads. Fracture mechanism of braided composites are closely related to the geometry of braids. In the present study, fracture mechanism of glass/epoxy braided composite cylinders is investigated under tensile loads. For this purpose, glass/epoxy braided composites were fabricated using braids with braiding angles of 30°, 45°, and 57° to find the role of fiber path on the fracture mechanism. To determine the fiber path, helixes on the cylinders with aforementioned angles was considered and analyzed. New fixtures (jaws) were designed and manufactured for tensile testing of cylindrical composites. Tensile tests were carried out on the prepared samples to evaluate the failure modes of composites. The SEM micrographs of samples are provided after tensile test. Various failure modes were observed regarding the angle of the braid. Fiber breakage, matrix fracture, and debonding are the dominant modes that occur in braided composites proportional to the angle of braids. Fiber breakage is the dominant mode in the 30° angle braid reinforced composite, while the dominant failure mode in the 57° angle braid reinforced composite is matrix fracture. In composites with a braid angle of 45°, a combination of fracture modes occurred. In addition, energy absorption as well as specific energy absorption (SEA) of braided composite cylinders were also investigated and obtained from load–displacement curves. The results showed that the reinforced composite with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.Highlights Fiber breakage is the dominant mode at the 30° angle braid reinforced composite. The dominant failure mode at the 57° angle braid reinforced composite is matrix fracture. In composites with the braid angle of 45°, a combination of fracture modes occurred. The composite reinforced with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.

The efficiency of the first-order reliability method (FORM) and the accuracy of Monte Carlo simulations (MCS) are coupled in probability-based designs of reinforced rock slopes, including a Hong Kong slope with exfoliation joints. Load–resistance duality is demonstrated and resolved automatically in a foundation on rock with a discontinuity plane. Other examples include the lengthy Hoek and Bray deterministic vectorial procedure for comprehensive pentahedral blocks with external load and bolt force, which is made efficient and more succinct before extending it to probability-based design via MCS-enhanced FORM. The FORM–MCS–FORM design procedure is proposed for cases with multiple failure modes. For cases with a dominant single failure mode, the time-saving importance sampling (IS) and the fast second-order reliability method (SORM) can be used in lieu of MCS. Two cases of 3D reinforced blocks (pentahedral and tetrahedral, respectively) with the possibility of multiple sliding modes are investigated. In the case of the reinforced pentahedral block, direct MCS shows that there is only one dominant failure mode, for which the efficient method of importance sampling at the FORM design point provides fast verification of the revised design. In the case of the reinforced tetrahedral block, there are multiple failure modes contributing to the total failure probability, for which the proposed MCS-enhanced FORM procedure is demonstrated to be essential. Comparisons are made between Excel MCS and MATLAB MCS.

Electronic systems under extreme shock and vibration environments including shock and vibration may sustain several failure modes simultaneously. Previous experience of the authors indicates that the dominant failure modes experienced by packages in a drop and shock frame work are in the solder interconnects including cracks at the package and the board interface, pad cratering, copper trace fatigue, and bulk-failure in the solder joint. In this paper, a method has been presented for failure mode classification using a combination of Karhunen Loeve transform with parity-based stepwise supervised training of a perceptrons. Early classification of multiple failure modes in the pre-failure space using supervised neural networks in conjunction with Karhunen Loeve transform is new. Feature space has been formed by joint time frequency analysis. Since the cumulative damage may be accrued under repetitive loading with exposure to multiple shock events, the area array assemblies have been exposed to shock and feature vectors constructed to track damage initiation and progression. Error Back propagation learning algorithm has been used for stepwise parity of each particular failure mode. The classified failure modes and failure regions belonging to each particular failure modes in the feature space are also validated by simulation of the designed neural network used for parity of feature space. Statistical similarity and validation of different classified dominant failure modes is performed by multivariate analysis of variance and Hoteling's T-square. The results of different classified dominant failure modes are also correlated with the experimental cross sections of the failed test assemblies. The methodology adopted in this paper can perform real-time fault monitoring with identification of specific dominant failure mode and is scalable to system level reliability.

This study proposes a system reliability analysis of rack storage facilities subjected to forklift colliding events. The proposed system reliability analysis consists of two steps: the first step is to identify dominant failure modes that most contribute to the failure of the whole rack facilities, and the second step is to evaluate the system failure probability. In the first step, dominant failure modes are identified by using a simulation-based selective searching technique where the contribution of a failure mode to the system failure is roughly estimated based on the distance from the origin in the space of the random variables. In the second step, the multi-scale system reliability method is used to compute the system reliability where the first-order reliability method (FORM) is initially used to evaluate the component failure probability (failure probability of one member), and then the probabilities of the identified failure modes and their statistical dependence are evaluated, which is called as the lower-scale reliability analysis. Since the system failure probability is comprised of the probabilities of the failure modes, a higher-scale reliability analysis is performed again based on the results of the lower-scale analyses, and the system failure probability is finally evaluated. The illustrative example demonstrates the results of the system reliability analysis of the rack storage facilities subjected to forklift impact loadings. The numerical efficiency and accuracy of the approach are compared with the Monte Carlo simulations. The results show that the proposed two-step approach is able to provide accurate reliability assessment as well as significant saving of computational time. The results of the identified failure modes additionally let us know the most-critical members and their failure sequence under the complicated configuration of the member connections.

Coal wall rib spalling, a frequent safety hazard in underground coal mining, is driven by the complex stress environment induced by mining-induced strata movement and dynamic loading from coal cutting equipment. Its severity is significantly exacerbated with increasing mining height, posing major threats to the safe operation of working faces. This study systematically investigates the failure mechanism and key influencing factors of coal wall rib spalling via an integrated framework combining theoretical analysis, FLAC³D finite difference numerical simulation, L25(5⁶) orthogonal testing, and grey relational analysis (GRA). Two dominant failure modes were identified: shear slip failure and tensile spalling failure, and shear slip failure is sensitive to factors such as coal bulk density and cohesion, while tensile spalling failure is more sensitive to factors including mining height. Six key influencing factors were determined and classified into three categories: coal seam occurrence conditions (mining height, coal bulk density), coal mass mechanical properties (cohesion, internal friction angle), and support parameters (hydraulic support intensity, shield guard horizontal supporting stress). Range analysis and GRA yielded highly consistent results: the grey relational degree of the factors is ranked as cohesion > internal friction angle > mining height > coal bulk density > hydraulic support intensity > shield guard horizontal supporting stress. This indicates that coal mass properties exert the dominant control on coal wall stability, followed by seam occurrence conditions, while support parameters have the weakest influence. The findings clarify the priority of rib spalling prevention, and provide critical theoretical guidance for formulating coal wall stability control schemes in high-cut fully mechanized mining faces.

This paper presents a qualitative design tool for evaluation of the risk for fluid power pitch systems. The design tool is developed with special attention to industry standard failure analysis methods and is aimed at the early phase of system design. Firstly, the concept of Fault Tree Analysis is used for systematic description of fault propagation linking failure modes to system effects. The methodology is conducted solely on a circuit diagram and functional behavior. The Failure Mode and Effects Criticality Analysis is subsequently employed to determine the failure mode risk via the Risk Priority Number. The Failure Mode and Effect Criticality Analysis is based on past research concerning failure analysis of wind turbine drive trains. Guidelines are given to select the severity, occurrence and detection score that make up the risk priority number. The usability of the method is shown in a case study of a fluid power pitch system applied to wind turbines. The results show a good agreement to recent field failure data for offshore turbines where the dominating failure modes are related to valves, accumulators and leakage. The results are further used for making design improvements to lower the overall risk of the pitch system. Copyright © 2017 John Wiley & Sons, Ltd.

Dominant mechanisms in stochastic plastic frames

<div class="htmlview paragraph">In complex systems there exist many elements and an associated large number of possible strength failure modes. If the overall reliability goal assigned to the strength failure modes is large and all the failure modes are assumed to be independent, then the reliability goals for each element designed on a strength basis can be very severe. It is shown that sets of strength failure modes are related through environmental considerations. This dependence leads to less severe reliability goals, and thus to lower total design weight, than that found when assuming all the strength failure modes to be independent. The dependence of the failure mode is then associated with the <u>a posteriori</u> behavior of systems, indicating that the strength failure modes can essentially be represented by a few dominant modes. Simple rules are then given for allocating the required overall reliability goal to the dominant strength failure modes, and in turn, to the elements designed from strength considerations.</div>

An equivalent structural stress-based fatigue evaluation framework for rib-to-deck welded joints in orthotropic steel deck

Modal Failure probability (MFP) has no unique definition in time-invariant analysis, and true MFPs cannot be obtained without information on load history. Knowledge of true MFPs of a structure is important for design, since different failure modes have different consequences. Therefore, dominant mode identification methods for structures with time-varying random loading are needed. To this end, a three-phase method based on the first passage probability is presented to identify systematically the dominant failure modes when loads and/or resistances are stochastic processes. In phase I, the modes with higher pseudo modal outcrossing rates are identified. In phase II, modes are chosen which refine the partial system state limit surface such that the total outcrossing rate of the modes selected in phase I is minimized. Modes selected in phases I and II with outcrossing rates below a tolerance level are discarded in phase III. A rigid-plastic frame structure is provided to illustrate the effectiveness of the method. Mathematical programming formulation based on the kinematic theorem for plasticity is used to carry out the maximization and minimization processes.

A unified fatigue life evaluation method for different failure modes of the repaired rib-to-deck joints in orthotropic steel decks

Experimental and analytical studies of base pipe pin connections under direct tension

In this research, the anisotropic behaviour of laminated sandstones, collected from southwest of Qom (central part of Iran), was evaluated using uniaxial compressive strength, point load and Brazilian tests. For this purpose, the eight rock blocks were selected. The rock samples were drilled at different direction with respect to the inclination angles (β) of 0, 30, 45, 60 and 90°. After specimen’s preparation and assessment of mineralogical and physical properties, specimens were subjected to uniaxial compressive strength, point load and Brazilian tests, and their strength and failure modes were evaluated at different inclination angles (β) between loading direction and lamination planes. Transitional angle, which indicates the change in dominant failure mode from parallel to the lamination to across the lamination, were also determined. The results indicate that the anisotropic behaviour of selected sandstones in uniaxial compressive strength test is different compared with the point load and Brazilian tests. Based on the results, the compressive strength anisotropy ratio of the studied sandstones is low, whereas for point load tests, the anisotropy ratio is obtained moderate. Finally, the different failure modes were classified for laminated sandstones.

A dominant failure mode in hot-mix asphalt (HMA) layers is material fatigue, occurring when the asphalt layer is repeatedly loaded by tensile stresses. The maximum stress arises at the bottom of the asphalt layer and, in consequence, crack development is initiated at the bottom. Various techniques are known that simulate bottom-up fatigue cracking in the laboratory. Fatigue failure is also observed on top of the pavement. Especially in cold climates, temperature-induced top-down cracking initiated at the pavement surface is a well-known failure mode. Usually, horizontal tensile stresses in the surface layer are smaller than stresses in the bottom layer. At cold temperatures and when temperature falls within a short period of time, the traffic-induced stress is superposed by temperature-induced stress, and the total stress may come up to the tensile strength of the material. In order to test the material's susceptibility to temperature-induced top-down fatigue cracking in the laboratory, the Uniaxial Cyclic Tensile Stress Test (UCTST) was established and recently introduced in European Standards (prEN 12697-46). In this test, a prismatic shaped HMA beam is subjected to a constant tensile load (representing the temperature-induced stress) which is superposed by a sinusoidal tensile load (representing the traffic load). This loading situation results in a visco-elastic strain response on the one hand, and in an accumulation of visco-plastic strain on the other. Different failure modes are observed in UCTST. In this paper, the failure modes occurring in UCTST, i.e. cracking of the specimen, stiffness decrease, and creep, are discussed based on the results from laboratory testing of nine different HMA and on variation of loading conditions.

The contributions of web construction, fiber, binder and interfacial properties. and binder distribution to nonwoven performance were studied. Some of these were found to have no effect on nonwoven strength but to affect modulus and hand. Although adhesive failure has often been regarded as the dominant failure mode. these observations show that the prevalent failure mode was due to the lack of binder cohesive strength. Addition of certain wetting agents, some of which are being used by nonwoven manufacturers, transferred the failure mode of a given binder-fiber combination into an adhesive one.