Bioimplant grade hot-rolled magnesium with equiaxed microstructure and basal texture was examined for fracture toughness(FT)anisotropy using fatigue pre-cracked single-edge notch bending specimens with the notch,an||,...Bioimplant grade hot-rolled magnesium with equiaxed microstructure and basal texture was examined for fracture toughness(FT)anisotropy using fatigue pre-cracked single-edge notch bending specimens with the notch,an||,⊥and 45°to rolling direction(RD).Due to adequate crack-tip plasticity,the size-independent elastic-plastic fracture toughness(JIC)were determined.Anisotropic JIC was ob-served due to different twin lamellae formation w.r.t.notch owing to the initial basal texture with{10¯10}and{11¯20}poles mostlyand⊥to RD.The out-of-plane tensile stresses activated the{10¯12}||10¯11||extension twins(ET)as usual with matrix-ET∑15b coincident site lattice boundary(CSLB)interfaces.While the in-plane tensile stress⊥to the crack-tip activated{10¯11}||10¯12||contraction twins(CT)that transform into{10¯11}-{10¯12}double twins(DT)with matrix-DT∑23b and∑15a CSLBs.For an||RD,large DT lamellae fraction formed at∼30°and few ETs at∼30°and∼90°to the notch with crack growth mainly via the∑23b/∑15a CSLB interfaces during FT.While,significant DT and ET lamellae developed at∼0°and∼60°with cracking via the matrix-DT∑23b/∑15a and matrix-ET||15b CSLBs for an⊥RD.The DT and ET lamellae activated at∼15°,and the crack propagated through∑15b for an∼45°to RD.The JIC and the crack-tip plastic zone decreases,while the elastic component of the J-integral(Jel)and the ET formation increases from an||,⊥,to∼45°to RD.The strain incompatibility of matrices was higher with the geometrically hard ETs than DTs.Thus,brittle interlamellar cracking occurred through the∑15b interfaces.In contrast,almost similar and higher crack-tip plasticity occurred in matrix and DT domains during crack propagation via||23b/||15a CSLBs.Crack growth through∑23b/||15a led to high JIC,both∑15b and||23b/||15a led to moderate JIC,and∑15b least JIC for an||,⊥and 45°to RD,respectively.展开更多
In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequen...In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.展开更多
基金financial support provided by the Science and Engineering Research Board (Ref. no.: ECR/2016/000125), Department of Science and Technology, Government of India
文摘Bioimplant grade hot-rolled magnesium with equiaxed microstructure and basal texture was examined for fracture toughness(FT)anisotropy using fatigue pre-cracked single-edge notch bending specimens with the notch,an||,⊥and 45°to rolling direction(RD).Due to adequate crack-tip plasticity,the size-independent elastic-plastic fracture toughness(JIC)were determined.Anisotropic JIC was ob-served due to different twin lamellae formation w.r.t.notch owing to the initial basal texture with{10¯10}and{11¯20}poles mostlyand⊥to RD.The out-of-plane tensile stresses activated the{10¯12}||10¯11||extension twins(ET)as usual with matrix-ET∑15b coincident site lattice boundary(CSLB)interfaces.While the in-plane tensile stress⊥to the crack-tip activated{10¯11}||10¯12||contraction twins(CT)that transform into{10¯11}-{10¯12}double twins(DT)with matrix-DT∑23b and∑15a CSLBs.For an||RD,large DT lamellae fraction formed at∼30°and few ETs at∼30°and∼90°to the notch with crack growth mainly via the∑23b/∑15a CSLB interfaces during FT.While,significant DT and ET lamellae developed at∼0°and∼60°with cracking via the matrix-DT∑23b/∑15a and matrix-ET||15b CSLBs for an⊥RD.The DT and ET lamellae activated at∼15°,and the crack propagated through∑15b for an∼45°to RD.The JIC and the crack-tip plastic zone decreases,while the elastic component of the J-integral(Jel)and the ET formation increases from an||,⊥,to∼45°to RD.The strain incompatibility of matrices was higher with the geometrically hard ETs than DTs.Thus,brittle interlamellar cracking occurred through the∑15b interfaces.In contrast,almost similar and higher crack-tip plasticity occurred in matrix and DT domains during crack propagation via||23b/||15a CSLBs.Crack growth through∑23b/||15a led to high JIC,both∑15b and||23b/||15a led to moderate JIC,and∑15b least JIC for an||,⊥and 45°to RD,respectively.
文摘In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.
