During the financial crisis, the delayed recognition of credit losses on loans and other financial instruments was identified as a weakness in existing incurred loss model of impairment stated by International Account...During the financial crisis, the delayed recognition of credit losses on loans and other financial instruments was identified as a weakness in existing incurred loss model of impairment stated by International Accounting Standards （IAS） 39, because it is believed that this delay might generate pro-cyclical effects. In response to the recommendations of G20, Financial Crisis Advisory Group （FCAG）, and other international bodies, the International Accounting Standards Board （IASB） has undertaken, since 2009, as a part of the project to replace IAS 39, a project （partially shared with Financial Accounting Standards Board （FASB）） aimed at introducing an expected loss model of impairment. Within the scope of this subset project, the IASB has previously issued two exposure documents proposing models to account for expected credit losses： an exposure draft （ED） Financial Instrument： Amortized Cost and Impairment, published in November 2009, and a supplementary document （SD） Financial Instrument： Impairment, published jointly with the FASB in January 2011. However, neither of the two proposals received strong support from interested parties. Recently, the IASB, after the FASB＇s decision to withdraw from the joint project and to develop a separate expected credit loss model based on a single measurement approach consisting in the sole recognition of lifetime expected credit losses, published a third proposal--Ahe so-called expected credit losses model （ED/2013/3 Financial Instruments： Expected Credit Losses）.展开更多
Dynamic crack propagation in brittle materials plays an important role in unJerstanding the fracture mechanism.Numerical simulations on crack propagation in the polymethyle methacrylate(PMMA)under explosive loads were...Dynamic crack propagation in brittle materials plays an important role in unJerstanding the fracture mechanism.Numerical simulations on crack propagation in the polymethyle methacrylate(PMMA)under explosive loads were carried out through Autodyn 3D code.Although the Johnson-Holmquist(JH-2)constitutive model has been widely treated as an acceptable scheme,it cannot improve the description in the post-failure response of material and reduce the mesh dependency,so the crack softening failure model are introduced in our present work based on two failure criterions.First,material parameters of JH-2 model,failure criterion,and crack softening failure model are determined from available data and calculations.The circular and rectangle thin plates are modeled to explore the fracture mechanisms for single-borehole and dual-borehole explosions.The simulation results well reproduced the entire dynamic evolutionary process of the crushed and fractured zones,crack initiation,propagation and arrest as well as secondary propagation,which successfully proved the relibilities of the combination of JH-2 constitutive model,failure criterion,and crack softening failure model and corresponding material parameters.For dual-borehole explosion,the crack linkage is well performed when borehole distance L is 20 and 30 cm;cracks are failed to link with each other at L=40 cm although main cracks have arrived into the opposite fractured zone.More importantly,it is found that the crack linkage mainly depends on L,which has an important effect on linkage style and its location.Despite a larger L makes more difficult in crack linkage,this difficulty lies not in the shortage of crack length,but in losing control of directional fracture of cracks between two boreholes.展开更多
A degradation model with a random failure threshold is presented for the assessment of reliability by the Bayesian approach. This model is different from others in that the degradation process is proceeding under pre-...A degradation model with a random failure threshold is presented for the assessment of reliability by the Bayesian approach. This model is different from others in that the degradation process is proceeding under pre-specified periodical calibrations. And here a random threshold distribution instead of a constant threshold which is difficult to determine in practice is used. The system reliability is defined as the probability that the degradation signals do not exceed the random threshold. Based on the posterior distribution estimates of degradation performance, two models for Bayesian reliability assessments are presented in terms of the degradation performance and the distribution of random failure threshold. The methods proposed in this paper are very useful and practical for multi-stage system with uncertain failure threshold. This study perfects the degradation modeling approaches and plays an important role in the remaining useful life estimation and maintenance decision making.展开更多
文摘During the financial crisis, the delayed recognition of credit losses on loans and other financial instruments was identified as a weakness in existing incurred loss model of impairment stated by International Accounting Standards （IAS） 39, because it is believed that this delay might generate pro-cyclical effects. In response to the recommendations of G20, Financial Crisis Advisory Group （FCAG）, and other international bodies, the International Accounting Standards Board （IASB） has undertaken, since 2009, as a part of the project to replace IAS 39, a project （partially shared with Financial Accounting Standards Board （FASB）） aimed at introducing an expected loss model of impairment. Within the scope of this subset project, the IASB has previously issued two exposure documents proposing models to account for expected credit losses： an exposure draft （ED） Financial Instrument： Amortized Cost and Impairment, published in November 2009, and a supplementary document （SD） Financial Instrument： Impairment, published jointly with the FASB in January 2011. However, neither of the two proposals received strong support from interested parties. Recently, the IASB, after the FASB＇s decision to withdraw from the joint project and to develop a separate expected credit loss model based on a single measurement approach consisting in the sole recognition of lifetime expected credit losses, published a third proposal--Ahe so-called expected credit losses model （ED/2013/3 Financial Instruments： Expected Credit Losses）.
基金the Key Research Foundation of Education Bureau of Sichuan Province(Grant No.17zd1122)the Natural Science Foundation of Southwest University of Science and Technology(Grant No.19zx7168)+2 种基金the Shock and Vibration of Engineering Materials and Struc-tures Key Laboratory of Sichuan Province(Grant No.I9kfgk07)the Sci-ence and Technology Department of Sichuan Province(Grant No.2021 YJ0525)National Natural Science Foundation of China(Grant No.11802255).
文摘Dynamic crack propagation in brittle materials plays an important role in unJerstanding the fracture mechanism.Numerical simulations on crack propagation in the polymethyle methacrylate(PMMA)under explosive loads were carried out through Autodyn 3D code.Although the Johnson-Holmquist(JH-2)constitutive model has been widely treated as an acceptable scheme,it cannot improve the description in the post-failure response of material and reduce the mesh dependency,so the crack softening failure model are introduced in our present work based on two failure criterions.First,material parameters of JH-2 model,failure criterion,and crack softening failure model are determined from available data and calculations.The circular and rectangle thin plates are modeled to explore the fracture mechanisms for single-borehole and dual-borehole explosions.The simulation results well reproduced the entire dynamic evolutionary process of the crushed and fractured zones,crack initiation,propagation and arrest as well as secondary propagation,which successfully proved the relibilities of the combination of JH-2 constitutive model,failure criterion,and crack softening failure model and corresponding material parameters.For dual-borehole explosion,the crack linkage is well performed when borehole distance L is 20 and 30 cm;cracks are failed to link with each other at L=40 cm although main cracks have arrived into the opposite fractured zone.More importantly,it is found that the crack linkage mainly depends on L,which has an important effect on linkage style and its location.Despite a larger L makes more difficult in crack linkage,this difficulty lies not in the shortage of crack length,but in losing control of directional fracture of cracks between two boreholes.
基金the National Natural Science Foundation of China(No.71371031)
文摘A degradation model with a random failure threshold is presented for the assessment of reliability by the Bayesian approach. This model is different from others in that the degradation process is proceeding under pre-specified periodical calibrations. And here a random threshold distribution instead of a constant threshold which is difficult to determine in practice is used. The system reliability is defined as the probability that the degradation signals do not exceed the random threshold. Based on the posterior distribution estimates of degradation performance, two models for Bayesian reliability assessments are presented in terms of the degradation performance and the distribution of random failure threshold. The methods proposed in this paper are very useful and practical for multi-stage system with uncertain failure threshold. This study perfects the degradation modeling approaches and plays an important role in the remaining useful life estimation and maintenance decision making.
