In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic te...In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic testing method(20 KHz) and rotary bending testing method(52.5 Hz),both at room temperatures,to establish stress versus cycles to failure(S-N) relationships.Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency,i.e.,the higher frequency produced an upper shift of the S-N curves.Fractographic analysis suggested that crack initiation and propagation behaviors had large differences:cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface,while in high-frequency tests,cracks mostly originated from a unique source of subsurface inclusions.Subsequently,frequency-involved modeling was proposed,based on the damage accumulation theory,which could well illustrate qualitatively those comparisons due to different loading frequencies.展开更多
In this work,a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed (APS) thermal barrier coatings (TBCs) over a wide range of mode mixities.For this mixed-mode test meth...In this work,a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed (APS) thermal barrier coatings (TBCs) over a wide range of mode mixities.For this mixed-mode test method,the analytical expressions for the energy release rate and stress intensity factors were derived based on the energy theory and the concept of "equivalence".The fidelity of these expressions was affirmed by selected finite element analysis.The experimental results showed that the critical energy release rate increased with the increase of the positive mode mixity,which was mainly due to the increase in contact/friction effect and plastic work dissipation with increasing shear mode loading.Furthermore,an elliptical interfacial failure criterion in terms of the stress intensity factors was proposed.The agreement between the experimental results in the literature and those in our work indicated that our test method and the corresponding analytical solutions can well determine the interfacial fracture toughness of the TBCs over a wide range of mode mixities.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10872105 and 51071094)
文摘In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic testing method(20 KHz) and rotary bending testing method(52.5 Hz),both at room temperatures,to establish stress versus cycles to failure(S-N) relationships.Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency,i.e.,the higher frequency produced an upper shift of the S-N curves.Fractographic analysis suggested that crack initiation and propagation behaviors had large differences:cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface,while in high-frequency tests,cracks mostly originated from a unique source of subsurface inclusions.Subsequently,frequency-involved modeling was proposed,based on the damage accumulation theory,which could well illustrate qualitatively those comparisons due to different loading frequencies.
基金supports from the National Natural Science Foundation of China(No. 10872105 and No. 51071094)
文摘In this work,a test method was developed to determine the interfacial fracture toughness of the air plasma sprayed (APS) thermal barrier coatings (TBCs) over a wide range of mode mixities.For this mixed-mode test method,the analytical expressions for the energy release rate and stress intensity factors were derived based on the energy theory and the concept of "equivalence".The fidelity of these expressions was affirmed by selected finite element analysis.The experimental results showed that the critical energy release rate increased with the increase of the positive mode mixity,which was mainly due to the increase in contact/friction effect and plastic work dissipation with increasing shear mode loading.Furthermore,an elliptical interfacial failure criterion in terms of the stress intensity factors was proposed.The agreement between the experimental results in the literature and those in our work indicated that our test method and the corresponding analytical solutions can well determine the interfacial fracture toughness of the TBCs over a wide range of mode mixities.
