Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cycli...Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cyclic deformation behavior of an as-cast Ti-22A1-20Nb-2V-1Mo-0.25Si(at.%)intermetallic compound in relation to its microstructure.The alloy containing an abundant fine lamellar O-Ti2AlNb phase exhibited a good combination of strength and plasticity,and superb fatigue resistance in comparison with other intermetallic compounds.Cyclic stabilization largely remained except slight cyclic hardening occurring at higher strain amplitudes.While fatigue life could be described using the common Coffin-Mason-Basquin equation,it could be better predicted via a weighted energy-based approach.Fatigue crack growth was characterized mainly by crystallographic cracking,along with fatigue striationlike features being unique to appear in the intermetallics.The results obtained in this study lay the foundation for the safe and durable applications of Ti2AlNb-based lightweight intermetallic compounds.展开更多
Alspach提出如下猜想:"设n是奇数并且每个m_1,m_2,…,m_h都是大于等于3而小于等于n的整数.若sum from i=1 to h m_i=n(n-1)/2,则K_n可以分解成圈G_(m_1),G_(m_2),…,G_(m_h)."用记号C(m_1^(n_1)m_2^(n_2)…m_s^(n_s))表示由n_...Alspach提出如下猜想:"设n是奇数并且每个m_1,m_2,…,m_h都是大于等于3而小于等于n的整数.若sum from i=1 to h m_i=n(n-1)/2,则K_n可以分解成圈G_(m_1),G_(m_2),…,G_(m_h)."用记号C(m_1^(n_1)m_2^(n_2)…m_s^(n_s))表示由n_i个m_i长圈,i=1,2,…,s组成的2-正则图.设Γ={C((2m_i)^(n_i)…(2m_s)^(n_s))|i∈[1,s]}.研究了循环(K_v,Γ)-分解的构造方法及其存在性问题,并且证明了Alspach猜想的一些特殊情况.展开更多
Failure cycles of notched round specimens under strain controlled cyclic loading are predicted using strain—life relations obtained from experiment for plain fatigue round specimens. For notched specimens, maximum st...Failure cycles of notched round specimens under strain controlled cyclic loading are predicted using strain—life relations obtained from experiment for plain fatigue round specimens. For notched specimens, maximum strain occurs at notch root and is different from applied controlled strain. The maximum strain is computed by appropriate Finite element analysis using the FE software ABAQUS. FE model and material parameters are validated by comparing the FE results and experimental results of LCF tests of round specimens. This value of maximum strain is used for prediction of failure cycles. Prediction is compared with the experimental results. The results show good matching.展开更多
In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations ...In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF) life of this alloy.A thermomechanical process was applied to induce fine-grained(FG) and coarse-grained(CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C(atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.展开更多
Discovering cyclic generalized association rules from transaction datbases can reveal the relationship of differ-ent levels of the taxonomies and display cyclic variations over time.Information about such variations i...Discovering cyclic generalized association rules from transaction datbases can reveal the relationship of differ-ent levels of the taxonomies and display cyclic variations over time.Information about such variations is great use of better identifying trends in associations and forecast-ing.Because cyclic rules are quite sensitive to a littlenoise,this paper uses the noise-ratio as the criterion of i-dentifing cydclic itemsets for dealing with the problem and utilizes the cycle-pruning technique to reduce the comput-ing time of the data mining process by exploiting the real-tionship between the cycle and generalized frequent item-sets.The paper gives the algorithm of mining cyclic gen-eralized itemsets(CGI).Experiment shows that the CGI algorithm can efficiently yield results.展开更多
The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces h...The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.展开更多
基金supported by the National Natural Science Foundation of China (NSFC)(Grant No. 51871168)the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of international research collaboration+4 种基金China Scholarships Council (CSC) for providing a PhD student scholarshipthe financial support by the Premier’s Research Excellence Award (PREA)NSERC-Discovery Accelerator Supplement (DAS) AwardCanada Foundation for Innovation (CFI)Ryerson Research Chair (RRC) program
文摘Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cyclic deformation behavior of an as-cast Ti-22A1-20Nb-2V-1Mo-0.25Si(at.%)intermetallic compound in relation to its microstructure.The alloy containing an abundant fine lamellar O-Ti2AlNb phase exhibited a good combination of strength and plasticity,and superb fatigue resistance in comparison with other intermetallic compounds.Cyclic stabilization largely remained except slight cyclic hardening occurring at higher strain amplitudes.While fatigue life could be described using the common Coffin-Mason-Basquin equation,it could be better predicted via a weighted energy-based approach.Fatigue crack growth was characterized mainly by crystallographic cracking,along with fatigue striationlike features being unique to appear in the intermetallics.The results obtained in this study lay the foundation for the safe and durable applications of Ti2AlNb-based lightweight intermetallic compounds.
文摘Alspach提出如下猜想:"设n是奇数并且每个m_1,m_2,…,m_h都是大于等于3而小于等于n的整数.若sum from i=1 to h m_i=n(n-1)/2,则K_n可以分解成圈G_(m_1),G_(m_2),…,G_(m_h)."用记号C(m_1^(n_1)m_2^(n_2)…m_s^(n_s))表示由n_i个m_i长圈,i=1,2,…,s组成的2-正则图.设Γ={C((2m_i)^(n_i)…(2m_s)^(n_s))|i∈[1,s]}.研究了循环(K_v,Γ)-分解的构造方法及其存在性问题,并且证明了Alspach猜想的一些特殊情况.
文摘Failure cycles of notched round specimens under strain controlled cyclic loading are predicted using strain—life relations obtained from experiment for plain fatigue round specimens. For notched specimens, maximum strain occurs at notch root and is different from applied controlled strain. The maximum strain is computed by appropriate Finite element analysis using the FE software ABAQUS. FE model and material parameters are validated by comparing the FE results and experimental results of LCF tests of round specimens. This value of maximum strain is used for prediction of failure cycles. Prediction is compared with the experimental results. The results show good matching.
基金the National Research Foundation of Korea(NRF)grant(Grant No.2021R1A2C1095139)funded by the the Ministry of Science and ICT(MSIT,Korea)。
文摘In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF) life of this alloy.A thermomechanical process was applied to induce fine-grained(FG) and coarse-grained(CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C(atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.
文摘Discovering cyclic generalized association rules from transaction datbases can reveal the relationship of differ-ent levels of the taxonomies and display cyclic variations over time.Information about such variations is great use of better identifying trends in associations and forecast-ing.Because cyclic rules are quite sensitive to a littlenoise,this paper uses the noise-ratio as the criterion of i-dentifing cydclic itemsets for dealing with the problem and utilizes the cycle-pruning technique to reduce the comput-ing time of the data mining process by exploiting the real-tionship between the cycle and generalized frequent item-sets.The paper gives the algorithm of mining cyclic gen-eralized itemsets(CGI).Experiment shows that the CGI algorithm can efficiently yield results.
文摘The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.
