Design reliable and safe LED （light emitting diode） lighting equipment for potentially explosive atmospheres should require knowledge about the possible failure modes of LED sources. Nowadays, LED technology potenti...Design reliable and safe LED （light emitting diode） lighting equipment for potentially explosive atmospheres should require knowledge about the possible failure modes of LED sources. Nowadays, LED technology potential is not adequately considered by IECEx （International Electrotechnical Commission system for certification to standards relating to equipment for use in explosive atmospheres） yet. Standards only consider LEDs adequate for Zone 1 when luminary is realized by the Ex-d protection strategy, or ifa big limitation in terms of power is guarantee, for Ex-i mode. In particular, Ex-d LED luminaries are obtained by using heavy, thick and expensive flameproof enclosures, entrusting safety only to the mechanical strength of the case. Luminous efficiency＇s also reduced since the glass used is very thick （10% reduction of approximately every 10 mm of thickness of the glass）. The paper shows a study about different possible causes of LED failure and their implication with explosive atmospheres, investigating whether LED technology can be used safely with other safety strategy like Ex-e, which can guarantee better performance and less cost.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
文摘Design reliable and safe LED （light emitting diode） lighting equipment for potentially explosive atmospheres should require knowledge about the possible failure modes of LED sources. Nowadays, LED technology potential is not adequately considered by IECEx （International Electrotechnical Commission system for certification to standards relating to equipment for use in explosive atmospheres） yet. Standards only consider LEDs adequate for Zone 1 when luminary is realized by the Ex-d protection strategy, or ifa big limitation in terms of power is guarantee, for Ex-i mode. In particular, Ex-d LED luminaries are obtained by using heavy, thick and expensive flameproof enclosures, entrusting safety only to the mechanical strength of the case. Luminous efficiency＇s also reduced since the glass used is very thick （10% reduction of approximately every 10 mm of thickness of the glass）. The paper shows a study about different possible causes of LED failure and their implication with explosive atmospheres, investigating whether LED technology can be used safely with other safety strategy like Ex-e, which can guarantee better performance and less cost.
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.
