Papers by Keyword: Fatigue

Abstract: Through establishing the fatigue risk model for mining workers, this author found out the relative factors about fatigue risk. According to the risk itself and all kinds of its types, this author fix on corresponding level, analyze the index and find out the risk with the biggest probability. Consequently it can provide scientific proof for some corporations to take corresponding measures.

Abstract: At Present, stress corrosion and corrosion fatigue causing durability degradation of concrete structure in the field of civil engineering become an important problem,and thus become a hot topic to study. But the research on it at home and abroad is still in stage of theoretical exploration. This paper using self-designed corrosion fatigue loading test device, studied in magnesium nitrate solution of concrete under the action of erosion strength increasing regularity, results show that the concrete strength by corrosion fatigue than fatigue specimen attenuation extent.

Abstract: This paper discusses the benefits to using direct strain measurements when undertaking a fatigue assessment of a railway bridge. The paper gives a brief overview of the assessment methodology for assessing fatigue in a bridge carrying a single track before outlining a method suitable for assessing multi-track bridges. The accuracy of a fatigue assessment depends on the level of knowledge of many different parameters including: an accurate loading history comprising axle loads and train frequencies over its service life; details of changes to the track form, including changes in the depth of ballast; and changes to the structure including damage or repairs. Many of these parameters are not known with certainty. However, using monitoring systems to measure the strain cycles in a bridge helps to address some of these uncertainties and hence improves the accuracy of the assessment.

Abstract: Recent studies have proved that there is no fatigue limit for metallic materials; the stress life curve continuously drops even after 10⁷ cycles. However, existing design codes assume that there is a fatigue limit. Therefore, it is important to use appropriate safety factors if existing codes are used for life evaluations. This paper first describes a method to extend high cycle fatigue stress life curves which are developed using tests on small scale specimens, to the gigacycle regime. Then the difference between the stress life curves of small scale specimens and full scale tests related to steel bridges are explained. Finally, the paper presents a case study on a fatigue critical element of a steel railway bridge to show the significance of the gigacycle regime for fatigue life evaluation.

Abstract: In this paper, Continuum Damage Mechanics (CDM) theory is applied to low cycle and high cycle fatigue problems. Damage evolution laws are derived from thermodynamic principles and the fatigue number of cycles to crack initiation is expressed in terms of the range of applied stresses, triaxiality function and material constants termed as damage parameters. Low cycle fatigue damage evolution law is applied to adhesively bonded single lap joint. Damage parameters as function of stress are extracted from the fatigue tests and the damage model. High cycle fatigue damage model is applied to fretting fatigue test specimens and is integrated within a Finite Element Analysis (FEA) code in order to predict the number of cycles to crack initiation. Fretting fatigue problems involve two types of analyses; namely contact mechanics and damage/fracture mechanics. The high cycle fatigue damage evolution law takes into account the effect of different parameters such as contact geometry, axial stress, normal load and tangential load.

Abstract: Fatigue characterization is an important concern for structural materials. The fatigue behaviour of aluminium (Al) composite reinforced with carbon nanotubes (CNT) is of interest besides its improved strength. In this study, tension-tension fatigue tests were conducted on monolithic Al and Al reinforced with 0.5, 1 and 2 weight percentages of CNT. Experimental results showed that the addition of CNTs significantly increased the number of load cycles to failure for each loading case. CNTs could slow fatigue crack propagation by crack-bridging and CNT frictional pull-out mechanisms. Cyclic softening was observed for both monolithic Al and Al-0.5CNT fatigued at an intermediate-high maximum stress of 120 MPa. TEM studies showed that the cyclic softening was attributed to the rearrangement of dislocations into lower potential energy configurations, i.e. parallel arrays and twin boundary dislocations.

Abstract: Fatigue tests on lead zirconate titanate (PZT) were performed by using single-edge-V-notched specimens under cyclic mechanical loading with or without superposition of a DC electric field. Fatigue life was prolonged by applying a DC electric field to the PZT ceramics. To estimate the domain contribution, fatigue tests on barium strontium titanate (BST) ceramics in both ferroelectric and paraelectric phase were carried out. The fatigue life of the ferroelectric phase was much shorter than that of the paraelectric phase. Comparing the fatigue lives of two PZT ceramics with different values of coercive electric field (E_c) revealed that the fatigue life of the PZT with higher E_c is about one order of magnitude longer than that with lower E_c when the stress-intensity factor of fatigue test is low. It is therefore concluded that non-180°domain switching probably deteriorates the fatigue life of ferroelectric ceramics.

Abstract: In this paper multiple fatigue cracks propagation are simulated in two-dimensional plates. Since re-meshing the cracked bodies in each increment of crack extension is a time-consuming and complicated procedure, numerical simulation of mixed-mode crack propagation with FEM is a difficulty. For this purpose, a FEM software is programmed and mesh refinement in each increment of crack is performed by Delaunay Refinement Algorithm. Using different refinement methods, complex boundaries such as multiple cracks and discontinuities which are closed together are easily refined by this algorithm. Crack propagation path is predicted using domain form of J-integral. Modified tensile stress (MTS) criterion is used to predict the crack propagation path in each increment. Different numerical examples illustrate the validation and reliability of present software.

Abstract: Gear plays an important role in the project, and its failure form has been widely concerned. This article does a detailed study of fatigue failure of the gear at home and abroad, and discusses the experimental method, numerical model, finite element simulation baking and does a forecast on its characteristics and prospects.

Abstract: The new offshore areas being explored in Brazil presents higher concentration of CO₂ compared with most existing offshore fields. The presence of these more aggressive environments has led to the development of new technologies. Due to the construction characteristics of flexible pipes, any increase in CO₂ concentration in the conveyed fluid will, in turn, increase the CO₂ concentration in the pipe annulus, subjecting the metallic armor layers to a more aggressive environment. Evaluation of the CO₂ effects of corrosion fatigue behavior in tensile armor wires is therefore of vital importance. A comprehensive corrosion fatigue experiment for tensile armor wires in environments up to 10 bar of CO₂, has been established and the experimental results have shown a fatigue life reduction in the tensile amour wires due to higher levels of CO₂.