The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
John J. Mecholsky - One of the best experts on this subject based on the ideXlab platform.
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relationship between Fractography fractal analysis and crack branching
Journal of The European Ceramic Society, 2020Co-Authors: John J. Mecholsky, D P Delellis, Nicholas A MecholskyAbstract:Abstract A critical part of failure analysis is to understand the fracture process from initiation through crack propagation. Crack propagation in brittle materials can produce crack branching patterns that are fractal in nature, i.e., the crack branching coefficient (CBC). There is a direct correlation between the CBC and strength, σ f : σ f ∝ C B C . This appears to be in conflict with the fractal dimensional increment of the fracture surface, D * , which is independent of strength and related to the fracture toughness of the material, K c : K c = E a 0 1 / 2 D * 1 / 2 , where E is the elastic modulus and a 0 , a characteristic dimension. How can D * be constant in one case and CBC be a variable in another case? This paper demonstrates the relationship between D * and C B C in terms of Fractographic parameters. Examples of fractal analysis in analyzing field failures, e.g., that involve comminution, incomplete fractures of components, and potential processing problems will be demonstrated.
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residual stress in glass indentation crack and Fractography approaches
Dental Materials, 2009Co-Authors: Chuchai Anunmana, K J Anusavice, John J. MecholskyAbstract:Objective To test the hypothesis that the indentation crack technique can determine surface residual stresses that are not statistically significantly different from those determined from the analytical procedure using surface cracks, the four-point flexure test, and fracture surface analysis.
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application of fracture mechanics to failure in manatee rib bone
Journal of Biomechanical Engineering-transactions of The Asme, 2006Co-Authors: Kari B. Clifton, Roger L. Reep, John J. MecholskyAbstract:Background. The Florida manatee (Trichechus manatus latirostris) is listed as endangered by the U.S. Department of the Interior. Manatee ribs have different microstructure from the compact bone of other mammals. Biomechanical properties of the manatee ribs need to be better understood. Fracture toughness (K C ) has been shown to be a good index to assess the mechanical performance of bone. Quantitative Fractography can be used in concert with fracture mechanics equations to identify fracture initiating defects/ cracks and to calculate the fracture toughness of bone materials. Method of approach. Fractography is a standard technique for analyzing fracture behavior of brittle and quasi-brittle materials. Manatee ribs are highly mineralized and fracture in a manner similar to quasi-brittle materials. Therefore, quantitative Fractography was applied to determine the fracture toughness of manatee ribs. Results. Average fracture toughness values of small flexure specimens from six different sizes of manatees ranged from 1.3 to 2.6 MPa(m) 1/2 . Scanning electron microscope (SEM) images show most of the fracture origins were at openings for blood vessels and interlayer spaces. Conclusions. Quantitative Fractography and fracture mechanics can be combined to estimate the fracture toughness of the material in manatee rib bone. Fracture toughness of subadult and calf manatees appears to increase as the size of the manatee increases. Average fracture toughness of the manatee rib bone materials is less than the transverse fracture toughness of human and bovine tibia and femur.
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Fractography determining the sites of fracture initiation
Dental Materials, 1995Co-Authors: John J. MecholskyAbstract:Fractography is the analysis of fracture surfaces. Here, it refers to quantitative fracture surface analysis (FSA) in the context of applying the principles of fracture mechanics to the topography observed on the fracture surface of brittle materials. The application of FSA is based on the principle that encoded on the fracture surface of brittle materials is the entire history of the fracture process. It is our task to develop the skills and knowledge to decode this information. There are several motivating factors for applying our knowledge of FSA. The first and foremost is that there is specific, quantitative information to be obtained from the fracture surface. This information includes the identification of the size and location of the fracture initiating crack or defect, the stress state at failure, the existence, or not, of local or global residual stress, the existence, or not, of stress corrosion and a knowledge of local processing anomalies which affect the fracture process. The second motivating factor is that the information is free. Once a material is tested to failure, the encoded information becomes available. If we decide to observe the features produced during fracture then we are rewarded with much information. If we decide to ignore the fracture surface, then we are left to guess and/or reason as to the cause of the failure without the benefit of all of the possible information available. This paper addresses the application of quantitative fracture surface analysis to basic research, material and product development, and "trouble-shooting" of in-service failures. First, the basic principles involved will be presented. Next, the methodology necessary to apply the principles will be presented. Finally, a summary of the presentation will be made showing the applicability to design and reliability.
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relationship between fractal geometry and Fractography
Journal of the American Ceramic Society, 1991Co-Authors: John J. Mecholsky, Stephen W FreimanAbstract:Fractal geometry has been used to describe irregular fracture surfaces in a quantitative way. The fractal dimensional increment has been related to the fracture toughness of the material through the elastic modulus and a characteristic structure parameter, a0. The study of Fractography has shown the relationship between the flaw/mirror size ratio and the fracture toughness. An experimental observation has shown that the fracture toughness is related to the elastic modulus through another structure parameter, b0. Combining all of these relationships leads to the conclusion that the fractal dimensional increment, D*, is directly related to the flaw/mirror size ratio. Experimental measurements of the fractal dimension and the flaw/mirror size ratio on glasses, a glass-ceramic, polycrystalline ceramics, and a single crystal all agree with the prediction. The implication of this finding is that there is a linear scaling law in operation at fracture between the energy of crack initiation and of microbranching and is reflected in the features on the fracture surface.
Horst Biermann - One of the best experts on this subject based on the ideXlab platform.
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application of in situ thermography for evaluating the high cycle and very high cycle fatigue behaviour of cast aluminium alloy alsi7mg t6
Ultrasonics, 2013Co-Authors: Dominik Krewerth, Anja Weidner, Horst BiermannAbstract:The present paper illustrates the application of infrared thermal measurements for the investigation of crack initiation point and crack propagation in the high-cycle and the very high-cycle fatigue range of cast AlSi7Mg alloy (A356). The influence of casting defects, their location, size and amount was studied both by Fractography and thermography. Besides internal and surface fatigue crack initiation as a further crack initiation type multiple fatigue crack initiation was observed via in situ thermography which can be well correlated with the results from Fractography obtained by SEM investigations. In addition, crack propagation was studied by the development of the temperature measured via thermography. Moreover, the frequency influence on high-cycle fatigue behaviour was investigated. The presented results demonstrate well that the combination of Fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation in the VHCF regime.
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Investigation of the Damage Behavior of Cast Steel 42CrMo4 During Ultrasonic Fatigue by Combination of Thermography and Fractography
Advanced Engineering Materials, 2013Co-Authors: Dominik Krewerth, Anja Weidner, Horst BiermannAbstract:The present paper illustrates the application of infrared thermography measurements for the investigation of fatigue behavior of different types of defects in the high-cycle fatigue range of cast steel 42CrMo4 alloy (1.732). The influence of several defects on the fatigue damage behavior was studied by the combination of Fractography and thermography. Different crack initiation times and locations of several defects were detected and evaluated in one specimen. Furthermore, a direct correlation of Fractography and thermography was carried out. The presented results demonstrate well that the combination of Fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation modes during ultrasonic fatigue of 42CrMo4 steel.
Dominik Krewerth - One of the best experts on this subject based on the ideXlab platform.
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application of in situ thermography for evaluating the high cycle and very high cycle fatigue behaviour of cast aluminium alloy alsi7mg t6
Ultrasonics, 2013Co-Authors: Dominik Krewerth, Anja Weidner, Horst BiermannAbstract:The present paper illustrates the application of infrared thermal measurements for the investigation of crack initiation point and crack propagation in the high-cycle and the very high-cycle fatigue range of cast AlSi7Mg alloy (A356). The influence of casting defects, their location, size and amount was studied both by Fractography and thermography. Besides internal and surface fatigue crack initiation as a further crack initiation type multiple fatigue crack initiation was observed via in situ thermography which can be well correlated with the results from Fractography obtained by SEM investigations. In addition, crack propagation was studied by the development of the temperature measured via thermography. Moreover, the frequency influence on high-cycle fatigue behaviour was investigated. The presented results demonstrate well that the combination of Fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation in the VHCF regime.
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Investigation of the Damage Behavior of Cast Steel 42CrMo4 During Ultrasonic Fatigue by Combination of Thermography and Fractography
Advanced Engineering Materials, 2013Co-Authors: Dominik Krewerth, Anja Weidner, Horst BiermannAbstract:The present paper illustrates the application of infrared thermography measurements for the investigation of fatigue behavior of different types of defects in the high-cycle fatigue range of cast steel 42CrMo4 alloy (1.732). The influence of several defects on the fatigue damage behavior was studied by the combination of Fractography and thermography. Different crack initiation times and locations of several defects were detected and evaluated in one specimen. Furthermore, a direct correlation of Fractography and thermography was carried out. The presented results demonstrate well that the combination of Fractography and thermography can give a significant contribution to the knowledge of crack initiation and propagation modes during ultrasonic fatigue of 42CrMo4 steel.
Martin Strangwood - One of the best experts on this subject based on the ideXlab platform.
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acoustic emission monitoring of split formation during charpy impact testing of high strength steel
Materials Science and Technology, 2012Co-Authors: Andrii Kostryzhev, R B Punch, Claire Davis, Martin StrangwoodAbstract:Acoustic emission (AE) monitoring has been used to detect split formation during room temperature low blow Charpy impact testing of high strength thick strip steels. The AE signal analysis identified separate signals originating from hammer impact, plastic deformation (verified using Charpy impact testing on mild steel with no splits) and split initiation/growth. The presence of splits was confirmed by sectioning and Fractography, and the splits were brittle in nature. A possible correlation between the AE signal features and fracture mode is presented.
H Badarinarayan - One of the best experts on this subject based on the ideXlab platform.
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influence of structural integrity on fatigue behavior of friction stir spot welded az31 mg alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Harish Rao, J B Jordon, Mark E Barkey, Y B Guo, H BadarinarayanAbstract:Abstract In this paper the fatigue behavior of the friction stir spot welded (FSSW) coupons of magnesium AZ31 alloy manufactured under different welding process conditions is investigated. Two sets of lap-shear coupons were made based on variation in plunge depth, tool rotation speed and tool geometry. Metallographic analysis of the untested FSSW coupons revealed differences in weld geometry and microstructure. Interfacial hooking of the faying surface was found to vary significantly between the two sets of process conditions. Microhardness test data revealed a large gradient in hardness profile. Results from the load controlled cyclic tests showed that lower tool rotation and shallower shoulder plunge depth led to better fatigue performance. Optical Fractography of the fatigued coupons revealed that fatigue cracks initiated at the weld interface in both sets of coupons. However, the fracture mode showed variability between the two process conditions. The Fractography analysis suggests that the effective top sheet thickness, interfacial hook and microstructure, which are largely determined by the process conditions, significantly affect the fatigue behavior of the friction stir spot welds in magnesium alloys.
