Short Time Evaluation of Metallic Materials’ Fatigue Potential Combining Destructive and Non-Destructive Testing Methods (original) (raw)
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Non-Destructive Testing of Metallic Structures
2007
Non destructive testing (NDT) is mechanism which helps in finding out of defects of any item before major harms happen to the item without affecting its usefulness. This thesis discusses the Non destructive testing of metallic structures. There are more than ten methods of NDT in metals, in this thesis the most important ones-Visual, Ultrasonic, X-ray and Penetrant testing are discussed in detail. Samples are also selected and experiments are conducted on each of the three methods. The experimental results are discussed and comparisons are made based on cost, accuracy, safety, time consumption, etc. Based on these comparisons conclusions and recommendations are made.
Aerospace Material Damage Characterization and Life Predictions
International Conference on Aerospace Sciences and Aviation Technology, 1997
There is currently a concerted global effort to produce hypersonic vehicles. Structural materials in such vehicles must able to withstand high temperatures and retain a high stiffness, while carrying significant stresses. Titanium 15-3 metal matrix composites reinforced with SIC (SCS-6) fibers are being investigated to see if they satisfy the requirements for applications in such hypersonic vehicles. However, there is a limited understanding of structural failure modes in such composites. Fatigue damage mechanisms were identified in metal matrix composites via destructive and nondestructive testing (acoustic emission technique). Based on experimental evidence a micromechanical modeling approache was developped for the prediction of fatigue life in such composite materials. The model involves the use of crack-tip shielding concepts, in the assessments of crack bridging phenomena during fatigue crack growth. In addition, an acoustic emission modeling was developped utilizing micromechanical modeling and fracture mechanics concepts. Fatigue life predictions were obtained and compared with the actual/measured fatigue lives. The current approach of non-destructive characterization to damage history and life prediction will lead to a new maintenance philosophy under realistic service conditions. Characterization as well as the location of fatigue damage under real service conditions will allow the airframe to utilize condition-based maintenance instead of programmed-depot maintenance.
Fatigue assessment of metallic materials beyond strain measurement
International Journal of Fatigue
The comprehensive characterization of microstructural changes caused by cyclic loading is of major importance for the understanding of basic fatigue mechanisms and for an optimized fatigue life calculation of metallic materials. Different mechanical parameters have been considered relevant to describe fatigue processes and to characterize damage accumulation. Among those plastic strain is dominating especially for metallic materials. However measuring this parameter can easily become a challenge because the proportions of plastic strain are usually small when compared to the governing elastic strains. Besides conventional extensometers additional measurement techniques have been introduced over the past years. Even magnetic and ultrasonic sensing which are very much associated with physical parameters being used in nondestructive testing has been moreover considered recently for the determination of fatigue relevant parameters resulting from constant and variable amplitude loading.
Tools for Assessing the Damage Tolerance of Primary Structural Components
Virtual Testing and Predictive Modeling, 2009
Fatigue considerations play a major role in the design of optimised flight vehicles, and the ability to accurately design against the possibility of fatigue failure is paramount. However, recent studies have shown that, in the Paris Region, cracking in high-strength aerospace quality steels and Mil Annealed Ti-6AL-4V titanium is essentially R ratio independent. As a result, the crack closure and Willenborg algorithm's available within commercial crack growth codes are inappropriate for predicting/assessing cracking under operational loading in these materials. To help overcome this shortcoming, this chapter presents an alternative engineering approach that can be used to predict the growth of small near-micron-size defects under representative operational load spectra and reveal how it is linked to a prior law developed by the Boeing Commercial Aircraft Company. A simple method for estimating the S-N response of 7050-T7451 aluminium is then presented.
PROCEDURE FOR THE EVALUATION OF THE ACCUMULATION OF DEFECTS IN METALLIC STRUCTURAL MATERIALS UNDER COMPLEX ELASTOPLASTIC LOADING, 2006
Within framework of the continual fracture mechanics, we describe the engineering approach to the assessment of scattered microdamage accumulation kinetics in metallic materials under elastoplastic loading conditions in case of plane stressed state. Automatized experimental stand and the respective investigation technique are discussed. The stand has been developed based on modification of the UMÉ-10T electromechanic test machine. State-of-the-art computer technologies and microprocessing hardware are incorporated in the stand automation. We present the technique of experimental assessment of damage accumulation kinetics in metallic structural materials under complex elastoplastic loading conditions with account of two different fracture (cleavage and shear) processes, which technique is based on measuring the specific electric resistance of the specimen.
Journal of Materials Engineering & Performance 2.pdf
This article evaluates a proposed analytical-experimental methodology by which the fatigue load levels leading to failure of structural components is inferred. The so-called Berkovitz method is recognized to depend fundamentally on a 1:1 relationship of micro-and macroscopic crack propagation rates. Compact tensile specimens of a high-strength aluminum alloy were fatigue tested at room temperature according to ASTM-E647, in plane-stress and plane-strain conditions, respectively. Unloading elastic compliance and low-magnification visual techniques monitored crack propagation rates. Topographical survey of fractured surfaces was carried out in a scanning electron microscope to measure striation spacing at constant-⌬K locations. By inputting these values in the Berkovitz model, the load spectrum applied during the fatigue testing could be derived. Research results have shown that, if correctly and carefully used, the assessed procedure provides accurate estimation of fatigue loads, so constituting a powerful tool during failure analysis of mechanical components operating in constant amplitude loading conditions.
Procedia Engineering, 2011
The comprehensive characterization of microstructural changes caused by cyclic loading is of major importance for the understanding of basic fatigue mechanisms and for an optimized fatigue life calculation of metallic materials. Beside conventional strain measurements in recent years temperature and electrical resistance measurements were additionally used for the determination of fatigue relevant data during constant and variable amplitude loading. This paper presents selected results of the cyclic deformation behaviour of the quenched and tempered steel SAE 4140 and the cast iron ASTM 80-55-06 (EN-GJS-600) based on mechanical stress-strain hysteresis, temperature and electrical resistance data. In general the resistivity of metals increases during cyclic loading as a function of the increasing defect density i. e. dislocation density, pores and microcracks. The electrical resistance offers additional information about the cyclic deformation behaviour also in the range of low loading amplitudes resulting in very low plastic deformation and in the case of materials with a very low ductility. Furthermore the electrical resistance is independent of a defined gauge length and also applicable to complex geometries like notched specimens. The used physical quantities are linked by cross-effects and directly related to fatigue induced microstructural changes in the bulk material.