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Time-dependent processes with high temperature fatigue of alloys
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Alert
Time-dependent processes with high temperature fatigue of alloys The nondestructive evaluation of the life of Alloy 800H suggests, as a preliminary conclusion, that ultrasonic absorption can be correlated with the amount of microcrack damage and thus provides a measure of the life left under life-cycle fatigue conditions. This is one of the findings in research undertaken at the Joint Research Centre of the Commission of the European Communities. The work is part of a concerted European effort on hightemperature materials for conventional energy generation and conversion systems using fossil fuels. It has two main objectives: the characterization of the timedependent fatigue behaviour of Alloy 800H and Inconel MA 6000, and the assessment of the potential of various N D T techniques with respect to the residual lifetime prediction in Alloy 800H.
The time-dependent fatigue behaviour of Alloy 800H was characterized in detail. A report presents an overview of the cycle deformation behaviour, cyclic stress/strain relationship and cyclic life of the material over a range of temperatures and frequencies. The deformation and failure mechanisms are identified and the accumulation of damage in terms of surface crack initiation and crack growth is quantified. The fatigue properties of Inconel MA 6000 were also explored. The cyclic deformation behaviour, cyclic stress/strain curves and cyclic lives are reported, and deformation and failure modes are presented and discussed.
Further information: a 56 page report, reference 3616-NDT, price £25.00 + £1.65 postage and packing, is available from TechAlert.
Neutron diffraction techniques to measure residual strain The use of neutron diffraction techniques to measure strain in advanced ceramic matrix and metal matrix composites is being investigated at the Argonne National Laboratory. Strain measurements have been acquired nondestructively for composites comprising silicon carbide whiskers embedded in alumina and for silicon carbon fibres embedded in titanium. Although at present neutron diffraction cannot be used on a routine basis for the nondestructive evaluation of advanced composites,
it is a powerful method for measuring bulk residual strains from which residual stresses can be calculated. The technique can be used to study fabrication processes, to validate or calibrate other techniques for measuring stress (for example, ultrasonic techniques) and to confirm the validity of model calculations. Strains measured in the whiskers of ceramic/ceramic composites were in reasonable agreement with those calculated using two different stress models: a plane strain composite cylinder model and a model based
on Eshelby's ellipsoidal inclusion theory.
Further information: a five page report, reference 3768-NDT, price £ 19.75 + £ 1.15 postage and packing, is available from TechAlert.
M icroindentation tests for thin films Work at the University of Tennessee has shown that the hardness and elastic modulus of thin films and ion-implanted layers on ceramic substrates can be determined using ultra-low-load microindentation tests. It is claimed that substrate effects are easily distinguished and that poor film adhesion can be detected by this method. A commercially available, computer controlled, standard ultra-low microindentation system was used to test thin films of chromium (50 nm thick) and hard carbon (100 nm thick) on sapphire and ALON (AI23027Ns). Tests were also conducted on ion-implanted samples of sapphire. The microindentation system operated with loads between 3 #N and 120 mN and was used in the constant displacement rate mode. This involves driving the indenter towards the surface of the test specimen at a constant rate, detecting the surface contact by a change in velocity. After the surface has been detected, the indenter is forced into the specimen at a different but still constant displacement rate.
Further information: an eight page report, reference 3722-NDT(M), microfiche price £12.50 + £1.88 VAT, or paper copy price £19.75 + £1.15 postage and packing, is available from TechAlert.
To o r d e r reports Unless otherwise indicated, reports are available from: TechAlert, Microinfo Ltd, PO Box 3, Newman Lane, Alton, Hants GU34 2PG, UK. Cheques should be in Pounds Sterling and drawn on a UK bank. Non-UK customers should add £2. The report's reference number should always be quoted.
388
NDT International December 1989
Alert
Time-dependent processes with high temperature fatigue of alloys The nondestructive evaluation of the life of Alloy 800H suggests, as a preliminary conclusion, that ultrasonic absorption can be correlated with the amount of microcrack damage and thus provides a measure of the life left under life-cycle fatigue conditions. This is one of the findings in research undertaken at the Joint Research Centre of the Commission of the European Communities. The work is part of a concerted European effort on hightemperature materials for conventional energy generation and conversion systems using fossil fuels. It has two main objectives: the characterization of the timedependent fatigue behaviour of Alloy 800H and Inconel MA 6000, and the assessment of the potential of various N D T techniques with respect to the residual lifetime prediction in Alloy 800H.
The time-dependent fatigue behaviour of Alloy 800H was characterized in detail. A report presents an overview of the cycle deformation behaviour, cyclic stress/strain relationship and cyclic life of the material over a range of temperatures and frequencies. The deformation and failure mechanisms are identified and the accumulation of damage in terms of surface crack initiation and crack growth is quantified. The fatigue properties of Inconel MA 6000 were also explored. The cyclic deformation behaviour, cyclic stress/strain curves and cyclic lives are reported, and deformation and failure modes are presented and discussed.
Further information: a 56 page report, reference 3616-NDT, price £25.00 + £1.65 postage and packing, is available from TechAlert.
Neutron diffraction techniques to measure residual strain The use of neutron diffraction techniques to measure strain in advanced ceramic matrix and metal matrix composites is being investigated at the Argonne National Laboratory. Strain measurements have been acquired nondestructively for composites comprising silicon carbide whiskers embedded in alumina and for silicon carbon fibres embedded in titanium. Although at present neutron diffraction cannot be used on a routine basis for the nondestructive evaluation of advanced composites,
it is a powerful method for measuring bulk residual strains from which residual stresses can be calculated. The technique can be used to study fabrication processes, to validate or calibrate other techniques for measuring stress (for example, ultrasonic techniques) and to confirm the validity of model calculations. Strains measured in the whiskers of ceramic/ceramic composites were in reasonable agreement with those calculated using two different stress models: a plane strain composite cylinder model and a model based
on Eshelby's ellipsoidal inclusion theory.
Further information: a five page report, reference 3768-NDT, price £ 19.75 + £ 1.15 postage and packing, is available from TechAlert.
M icroindentation tests for thin films Work at the University of Tennessee has shown that the hardness and elastic modulus of thin films and ion-implanted layers on ceramic substrates can be determined using ultra-low-load microindentation tests. It is claimed that substrate effects are easily distinguished and that poor film adhesion can be detected by this method. A commercially available, computer controlled, standard ultra-low microindentation system was used to test thin films of chromium (50 nm thick) and hard carbon (100 nm thick) on sapphire and ALON (AI23027Ns). Tests were also conducted on ion-implanted samples of sapphire. The microindentation system operated with loads between 3 #N and 120 mN and was used in the constant displacement rate mode. This involves driving the indenter towards the surface of the test specimen at a constant rate, detecting the surface contact by a change in velocity. After the surface has been detected, the indenter is forced into the specimen at a different but still constant displacement rate.
Further information: an eight page report, reference 3722-NDT(M), microfiche price £12.50 + £1.88 VAT, or paper copy price £19.75 + £1.15 postage and packing, is available from TechAlert.
To o r d e r reports Unless otherwise indicated, reports are available from: TechAlert, Microinfo Ltd, PO Box 3, Newman Lane, Alton, Hants GU34 2PG, UK. Cheques should be in Pounds Sterling and drawn on a UK bank. Non-UK customers should add £2. The report's reference number should always be quoted.
388
NDT International December 1989