Papers by Keyword: Stress Concentration

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Authors: Li Bin Zhao, Feng Rui Liu, Jian Yu Zhang
Abstract: 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.
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Authors: A. Arteiro, Giuseppe Catalanotti, J. Xavier, P.P. Camanho
Abstract: A new model based on Finite Fracture Mechanics (FFMs) has been proposed to predict the open-hole tensile strength of composite laminates [1]. Failure is predicted when bothstress-based and energy-based criteria are satisfied. This model is based on an analytical solution, and no empirical adjusting parameters are required, but only two material properties: the unnotched strength and the fracture toughness. In the present work, an extension of the proposed FFMs model to predict the notched response of composite laminates with notch geometries other than a circular opening [2] is presented and applied to the prediction of size effects on the tensile and compressive notched strength of composite laminates. The present model is also used to assess the notch sensitivity and brittleness of composite laminates by means of versatile design charts and by the identification of a dimensionless parameter designated as notch sensitivity factor. A further extension of the FFMs model is proposed, which takes into account the crack resistance curve of the laminate in the model's formulation, and it is used to predict the large damage capability of a non-crimp fabric thin-ply laminate [3].
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Authors: Timothy J. Harrison, Bruce R. Crawford, Graham Clark, Milan Brandt
Abstract: This paper presents a model that predicts the stress field around intergranular corrosion. The stress analysis is conducted in ABAQUS via a Python input script, which is written in Igor Pro. The intergranular corrosion path is described using a Monte-Carlo Markov Chain based on the materials grain size distribution and probability that the corrosion will turn at a grain boundary junction. The model allows a complete analysis of the stresses resulting from intergranular corrosion around a fastener hole of any size. As fatigue initiation is most likely to occur at the highest stress concentration, this model gives an understanding of which of the features of intergranular corrosion are most critical and can allow for the development of beta solutions for crack growth. This model has been applied to 7075-T651 extruded aluminum alloy from a legacy era aircraft but can be readily applied to any material where the microstructure is known and can be described using a statistical distribution.
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Authors: Qing Song Tu, Wei Min Zhang, Li Huang, Cheng Feng Chen, Qiu Yong
Abstract: The relations between stresses and leakage magnetic signal of concentration area of the airplane’s landing gear under varying load were studied. The finite element method was used to calculate the stress of axle under different conditions; An experiment was designed to simulate the stress status under the bending moment, the slight magnetic signals on specimen were measured, and the relation of the signals and stress was studied. The new testing method was explained with the theory of ferromagnetic and the significance of this technique for detecting defects of the airplane structural part was discussed. The safety of airplane’s main bearing parts plays an important role during its operation and it often comes to bad situation of fatigue damage for stress concentration [1, 2]. To prevent the breaking down of structural parts and get rid of big accidents, it becomes important and necessary to find out the early concentration and damage zone, and to make some certain examination of damage and stress status [3]. The method of magnetic memory testing would be effective for the confirming of stress concentration zone in the equipment or structural parts, and could lead the way ahead the matters of fatigue analysis, evaluation of equipment life and technological design. The method can detect the endurance failure of the airplane’s undercarriage shaft, which is composed of ferromagnetic materials, and that provides the experimental basis for the prevention of parts’ fatigue defects.
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Authors: Justin O. Karl, Andrew T. Copeland, Amy K. Besio
Abstract: The behavior of parts subjected to simultaneous thermal and mechanical fatigue loads is an area of research that carries great significance in the power generation, petrochemical, and aerospace industries. Machinery with expensive components undergo varying applications of force while exposed to variable temperature working fluids. An example case is found in steam turbines, which subject stainless steel blades to cyclic loads from rotation as well as the passing of heated gases. Accurate service life prediction is especially challenging due to the thermo-mechanical loading being present on the complex geometric profile of the blades. This research puts forth a method for determining crack initiation lifetimes in variably-notched type 304 austenitic stainless steel specimens subjected to differing fatigue and thermo-mechanical fatigue conditions. A base analytical model and genetic algorithm were used to develop phenomenology-informed predictions that fall within a factor of two of the actual crack initiation times.
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Authors: Zhi Xue Wu
Abstract: A gradientless method for two-dimensional shape optimization is developed based on the magnitude of local relative-stress difference along the design boundary. The design boundary is modeled by using cubic splines, which are determined by a number of control points. The optimal shape of a design boundary with constant stress is achieved iteratively by moving control points consecutively (correspondingly, changing the shape of the design boundary) by an amount depending on the relative-stress difference between two neighboring boundary points. The key feature of the optimization method is that no arbitrary threshold stress is required. The result quality in terms of accuracy and efficiency are tested and discussed with several finite element analysis examples.
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Authors: Md. Shafiul Ferdous, Kaito Naka, Chobin Makabe, Tatsujiro Miyazaki
Abstract: Most of the failure accidents of machine equipment are related to the fatigue crack initiation and growth. Therefore, some research was performed to inspect crack initiation and to repair the cracked materials. Those studies are important for the safe operation of machines and to extend the machine life. We have shown some simple methods for arresting crack growth. Those methods are introduced in the present paper. First, a method of drilling stop holes near the crack tip is shown. In this method, additional holes were drilled in the vicinity of the main stop hole. Second, the method for inserting pins into stop holes is shown. Third, a method of applying a crack arrester for stopping the growth of long cracks is shown.
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Authors: Keyoung Jin Chun, Ho Jung Li
Abstract: Mandibular first premolars in superlative state were scanned by a Micro-CT. Data were obtained from the scanned 2-D images, and reconstructed into 3-D models for FEA, at which point stress distribution of the inner and outer part of the tooth were shown. It was found that when compared with the teeth data used as a standard by G. V. Black, the aspect of the external morphology of the teeth is comparatively small regardless of gender. Also, differences exist between the Micro-CT data and G. V. Black’s data. This study also presents the internal morphological data that was not shown in G. V. Black’s data. The dentin size is larger than the enamel size in both males and females in the case of the internal morphological data. It is found that the stress was concentrated on the cervical line, and the stress varied around the boundary between dentin and enamel within the teeth. It is also revealed that the stress varied at the boundary surface between dentin and pulp. The results using a Micro-CT and stress analysis may reveal the cause of the abfraction, and bring up a guideline for endodontic treatment.
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Authors: Michele Buonsanti, Antonella Pontari
Abstract: A new stress function modelling the fails in biological tissue is here proposed. Under the assumption that the cell membrane may be modelled as neo-Hookean materials, we develop the problem in the framework of non-linear elasticity. We attempt to model the ice nucleation phenomenon when freezing and thawing occurs in cellular cryo-preservation. The ice seed generated surface can be either soft or wrinkled and, when the latter emerges a punch contact against the cell membrane takes place. Restricting our attention on opportune mono-dimensional sub-set, we extend the multiple critical points theorem at our model. We find a particular solution in agreement to the classical fracture models besides a response function in accordance to the stress and strain field distribution in biological materials.
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