Search

This paper considers non-destructive evaluation techniques for integrity of structural materials of nuclear power plants. To increase the safety and reliability of long term operating plants, the exact remaining life of each component should be predicted by estimating material states such as the degree of degradation and mechanical states affecting the remaining life. Mechanical fatigue (for instance, degradation and residual stress) and plastic deformation (e.g. mechanical states) have been considered. Conventional flaw detection techniques cannot be applied to estimate such material states without the apparent geometrical changes. On the other hand, mechanical, electromagnetic or thermal properties of the material may change by several mechanisms. Several NDE techniques are proposed for the purpose and they are acoustic impedance method using phased array transducer, magnetoacoustoelasticity, magnetic flux leakage testing (MFLT), and thermograph combined with magnetic heating. Feasibility of the proposed techniques is discussed by applying them to typical carbon steel specimens. [ABSTRACT FROM AUTHOR]

The fatigue is the most common way of structural imperfection and, over the time, it has been a problem to the imposed requests and the type of applied load. In this paper, there is a study of the way the resistance fatigue ASTM A-36 is made among two environments: refrigerated and immerged into water at 5 atm hydrostatic pressure through bending tension fatigue tests. After that, some analyses and comparative results with the tested material were carried out. For this study, a mechanism was developed to test fatigue for bending tension to be used inside and outside hyperbaric chamber for the hydrostatic pressure simulation. This study is worth because any resistance confirmation does not exist in immerged fatigue of virgin materials; in other words, all the tests of fatigue were or have being accomplished in materials done in the air. Curves S-N were determined for each atmosphere. The methodology used for verification of resistance to the fatigue was the regression model from a data originated from accelerated life tests and it was possible to verify the environment influence in the phenomenon of the fatigue. [ABSTRACT FROM AUTHOR]

Most of energy fluids and also water are transported over very long distance by pipelines. There is a quite large spectrum of situations defined by: nature and pressure of the transported fluid, environmental and political situations, and economical constraints. If a pipeline is damaged and becomes unable to continue its service or presents some risks towards the local population, or is an economical challenge, the question of repairing appears. Therefore, the technical choices should be optimized with respect to the induced costs and to the social, economical and, perhaps, political costs. This paper will present various situations and the available repairing solutions, with respect to their costs in view to be a guide for the person in charge to make decision. [ABSTRACT FROM AUTHOR]

The paper presents experimental data on the fatigue of NCFs, with special emphasis on the development of damage, i.e. the crack density, stiffness degradation and fatigue life under multi-axial loading. Non-crimp-fabrics (NCF) consist of several sub-layers with different orientations, all stitched together by a stitching yarn. Its lay-up can be tailored to specific needs. It offers cost-savings in production processes because instead of laying several single layers under different orientations into a mould it is possible to lay just one NCF that includes all sublayers. One disadvantage is the stitching that causes local inhomogenities and fiber misalignment in the material. [ABSTRACT FROM AUTHOR]

The present paper deals with the fracture analysis of the frame of a very large pump. The complex geometry of the structure as well as the loading conditions were responsible of premature fracture failures localized in the neighborhood of the bolted connection between the column pipe and the basement plate. Retrofitting solutions and appropriate countermeasures were proposed after long lasting hydrodynamic and structural analyses that needed to account for very strict operational and time constraints. The fracture strength as well as the vibration behavior of the structure were considered taking advantage of both numerical FE calculations and experimental in-situ measurements. The parallel numerical and experimental analyses leaded to a set of modifications of the structure hereunder described in detail. The integration among experimental and theoretical results concurred to obtain a suitable solution for a quite complex case study because it allowed improving aspects related to both the strength and the loading conditions of the structure. [ABSTRACT FROM AUTHOR]

Cobalt-based alloys are known for their excellent wear resistance, particularly under high temperature and corrosive environments. However the cast cobalt-based alloys have relatively high brittleness, and low toughness, due to their coarse carbide structure. This paper aims to comprehend if carbide refinement, caused by changing the processing route from sand casting to powder consolidated Hot Isostatic Pressing (HIPing), can improve the tribo-mechanical properties of cobalt-based alloys. The alloy selected for this investigation had a nominal wt.% composition of Co-30Cr-14W-1C, which is similar to the composition of the commercially available Stellite®4 alloy. The Hot Isostatic Pressed (HIPed) alloy had a much finer microstructure than the cast alloy, which showed a typical hypoeutectic dendritic microstructure. Both alloys had similar hardness. Although the cast alloy showed slightly better abrasive and sliding wear resistance than the HIPed alloy due to their coarser eutectic carbides, the HIPed alloy had a significant advantage on the impact toughness and contact fatigue performance. The results of this comparative investigation indicated that the HIPed alloy had an attractive combination of tribo-mechanical properties, i.e. improved impact and fatigue resistance, whilst preserving the high hardness and good wear resistance associated with the cast alloy, making it suitable for relatively higher stress applications. [ABSTRACT FROM AUTHOR]

This chapter is intended for readers who do not have a background in bone biomechanics. It gives a description of bone, highlighting its complex and hierarchical structure, starting at the macroscopic scale from an entire bone, such as the femur, down to the nanoscopic scale and its basic components: the collagen fibers and the mineral crystals. Then, some definitions and concepts of biomechanics are given in relation to the hierarchical structure of bone. The goal is to define the main parameters that can be used to assess bone mechanical competence. Some mechanical features are accessible using the quantitative ultrasound (QUS) technologies that are presented in subsequent chapters. Finally, the clinical context in which QUS has been developed is described. Diagnosis and follow-up of osteoporosis is a major public health problem in which QUS can play a role. [ABSTRACT FROM AUTHOR]

The ice axe is an essential tool for any mountaineer climbing in icy conditions. Ice axes are often used for climbing frozen waterfalls and icy rock faces. One of the techniques used in such climbs is known as torquing. This technique involves placing the pick of the ice axe into a crack and pulling on the ice axe handle to wedge the pick in the crack to give purchase for the climber. This technique was initially frowned upon by ice axe manufacturers as the pick was not designed for such loading, but it has become an accepted climbing technique and the manufacturers have modified their product accordingly. There have been a number of ice pick failures due to fatigue, where the crack was initiated at the root of the ice pick tooth. It has been suggested that torquing is responsible for these failures. In this study the ice axe pick was modelled using three dimensional elements. Two cases were analysed: the first a static finite element analysis assuming the tip of the pick is clamped and the second a transient analysis modelling the tip in a crack in the rock. The results showed that in the static case the highest stresses were not at the root of a tooth, but there were tensile stress concentrations in the root of the teeth nearest the handle. The transient analysis revealed a high shear stress at the root of the two teeth nearest the axe handle. In both cases these may result in the fatigue failure of an ice pick with the crack initiating at the root of a tooth. [ABSTRACT FROM AUTHOR]

This article describes a general framework for detecting accident-prone fatigue states based on prosody, articulation and speech quality related speech characteristics. The advantages of this real-time measurement approach are that obtaining speech data is non obtrusive, and free from sensor application and calibration efforts. The main part of the feature computation is the combination of frame level based speech features and high level contour descriptors resulting in over 8,500 features per speech sample. In general the measurement process follows the speech adapted steps of pattern recognition: (a) recording speech, (b) preprocessing (segmenting speech units of interest), (c) feature computation (using perceptual and signal processing related features, as e.g. fundamental frequency, intensity, pause patterns, formants, cepstral coefficients), (d) dimensionality reduction (filter and wrapper based feature subset selection, (un-)supervised feature transformation), (e) classification (e.g. SVM, K-NN classifier), and (f) evaluation (e.g. 10-fold cross validation). The validity of this approach is briefly discussed by summarizing the empirical results of a sleep deprivation study. [ABSTRACT FROM AUTHOR]