BACKGROUND Talar fractures are exceedingly rare in childhood.There are very few studies on the clinical aspects,the long-term outcomes and the appropriate treatment of these fractures in pediatric patients.The mechani...BACKGROUND Talar fractures are exceedingly rare in childhood.There are very few studies on the clinical aspects,the long-term outcomes and the appropriate treatment of these fractures in pediatric patients.The mechanism of trauma consists of the application of a sudden dorsiflexion force on a fully plantar-flexed foot.Traumatic mechanism,symptoms and imaging of injuries of the talar head are similar to transitional fractures that are normally described at the distal epiphysis of the tibia:the so-called transitional fracture is defined as an epiphyseal injury when the growth plate has already started to close.CASE SUMMARY A thirteen-year-old girl reported a high-energy trauma to her right foot,due to falling from her horse.X-rays at the Emergency Department were negative.Because of persistent pain,the patient was assessed by an orthopedic surgeon after two weeks and computed tomography scans revealed a misdiagnosed displaced shear-type fracture of the talar head.Hence,surgical open reduction and fixation with two headless screws was performed.The girl was assessed regularly,and plain films at follow-up revealed complete healing of the fracture.Within six months after surgery,the patient returned to pre-injury sport activities reporting no complications.CONCLUSION Injuries of the talar head in childhood should be considered as transitional fractures.Open reduction with internal fixation aims to reduce malalignment and osteoarthritis.Computed tomography scans are recommended in these cases.展开更多
The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Anal...The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Analysis of the fracture process by the theory of thermal activation suggests that the fracture activation energy approximates to the bond energy of the{100}of a unit cell.The toughness can be resolved into two parts,J-(fd)=J_a+J_l,where J_a is the athermal part,being independent on temperature and loading rate,while J_l=(K/K_o)^(1/n)exp(Q_f/nkT),which controls the fracture process is temperature and load- ing rate dependent.The transition of fracture mechanism caused by both temperature and loading rate is associated with the thermal movement of atoms.展开更多
This work focused on the low-cycle fatigue （LCF） behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding （NG-SAW） process via multi-pass and multi-layer tec...This work focused on the low-cycle fatigue （LCF） behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding （NG-SAW） process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain （CSS） curve and Manson-Coffin （M-C） curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal （BM） at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone （OTZ） at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV- OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.展开更多
The impact toughness of EN-GJS-400-18-LT ductile iron was measured by Charpy V-notch impact test at temperature between-80 and 20℃.The fracture properties were tested under instrumented impact loading.Total impact fr...The impact toughness of EN-GJS-400-18-LT ductile iron was measured by Charpy V-notch impact test at temperature between-80 and 20℃.The fracture properties were tested under instrumented impact loading.Total impact fracture energy,crack initiation and propagation energy,dynamic loads and the ductile to brittle temperature were measured.Three-dimensional reconstruction of impact fracture morphology was accomplished by confocal laser scanning microscope.The results of quantitative fractography indicate that cleavage fracture produces flatter fracture surfaces accompanying with less absorbed energy during the impact fracture process.It indicates that fracture roughness has a close relationship with crack propagation energy at low temperature.展开更多
文摘BACKGROUND Talar fractures are exceedingly rare in childhood.There are very few studies on the clinical aspects,the long-term outcomes and the appropriate treatment of these fractures in pediatric patients.The mechanism of trauma consists of the application of a sudden dorsiflexion force on a fully plantar-flexed foot.Traumatic mechanism,symptoms and imaging of injuries of the talar head are similar to transitional fractures that are normally described at the distal epiphysis of the tibia:the so-called transitional fracture is defined as an epiphyseal injury when the growth plate has already started to close.CASE SUMMARY A thirteen-year-old girl reported a high-energy trauma to her right foot,due to falling from her horse.X-rays at the Emergency Department were negative.Because of persistent pain,the patient was assessed by an orthopedic surgeon after two weeks and computed tomography scans revealed a misdiagnosed displaced shear-type fracture of the talar head.Hence,surgical open reduction and fixation with two headless screws was performed.The girl was assessed regularly,and plain films at follow-up revealed complete healing of the fracture.Within six months after surgery,the patient returned to pre-injury sport activities reporting no complications.CONCLUSION Injuries of the talar head in childhood should be considered as transitional fractures.Open reduction with internal fixation aims to reduce malalignment and osteoarthritis.Computed tomography scans are recommended in these cases.
文摘The dynamic fracture toughness of a mild steel has been studied at different loading rates and temperatures.The material exhibits a transition from tough to brittle fracture with the chang- ing loading rate alone.Analysis of the fracture process by the theory of thermal activation suggests that the fracture activation energy approximates to the bond energy of the{100}of a unit cell.The toughness can be resolved into two parts,J-(fd)=J_a+J_l,where J_a is the athermal part,being independent on temperature and loading rate,while J_l=(K/K_o)^(1/n)exp(Q_f/nkT),which controls the fracture process is temperature and load- ing rate dependent.The transition of fracture mechanism caused by both temperature and loading rate is associated with the thermal movement of atoms.
文摘This work focused on the low-cycle fatigue （LCF） behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding （NG-SAW） process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain （CSS） curve and Manson-Coffin （M-C） curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal （BM） at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone （OTZ） at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV- OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude.
文摘The impact toughness of EN-GJS-400-18-LT ductile iron was measured by Charpy V-notch impact test at temperature between-80 and 20℃.The fracture properties were tested under instrumented impact loading.Total impact fracture energy,crack initiation and propagation energy,dynamic loads and the ductile to brittle temperature were measured.Three-dimensional reconstruction of impact fracture morphology was accomplished by confocal laser scanning microscope.The results of quantitative fractography indicate that cleavage fracture produces flatter fracture surfaces accompanying with less absorbed energy during the impact fracture process.It indicates that fracture roughness has a close relationship with crack propagation energy at low temperature.
