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Fractography
About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.
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TL;DR: In this article, the results of the fractographical analysis of fish-eye cracks that were formed in plasma-nitrided steel specimens under symmetrical bending, symmetrical torsion and biaxial in-phase bending-torsion loading combinations were presented.
29 citations
TL;DR: In this paper, a heterogeneous nucleation phenomenon in the cast AMMCs was studied by using optical microscopy, X-ray diffraction and scanning electron microscopy to identify the primary aluminium phase which nucleated heterogeneously on TiAl3 particles with a small lattice disregistry while their crystallographic orientation relationship was (001)TiAl3 // (100)Al.
Abstract: In the present research, aluminium metal matrix composites (AMMCs) with different weight percentages of TiAl3 particles were fabricated by in situ stir casting process. A heterogeneous nucleation phenomenon in the cast AMMCs was studied. Microstructural characterisation was investigated by optical microscopy, X-ray diffraction and scanning electron microscopy. Tensile test was carried out in order to identify the mechanical properties of composites after aging. The primary aluminium phase which nucleated heterogeneously on TiAl3 particles has been identified with a small lattice disregistry while their crystallographic orientation relationship was (001)TiAl3 // (100)Al. The microstructure analysis revealed uniform distribution of reinforcements, grain refinement and clean TiAl3/Al interface in specimens. The mechanical results showed that the addition of up to 1 wt-%Ti led to an improvement in the tensile strength and ductility as compared against matrix. Fractography of the specimens showed that ...
29 citations
29 citations
TL;DR: In this article, the authors investigated the fracture pattern of polymer crowns under compressive loads using finite element and fractography analyses and found that the fracture occurred from the occlusal to the cervical direction.
Abstract: Purpose: This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses. Materials and Methods: Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resincores.Crownswerefabricatedusingtheceramicslisted,cementedwithdual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests,andfracturedspecimenswerevisuallyinspectedunderastereomicroscope(20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography. Results: Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction. Conclusions: Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluatedbeforeclinicaluseduetothehighincidenceoffailurewithtoothinvolvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.
29 citations
TL;DR: In this paper, the fracture path was examined by observing the side surface in a partially ruptured specimen and the relationship of the fracture facets to the microstructures was established by simultaneously observing the fracture surface and the adjacent side surface simultaneously.
Abstract: The fracture mode and crack propagation behavior of brittle fracture at 77 and 4 K in an 18Cr-18Mn-0.7N austenitic stainless steel were investigated using optical and scanning electron microscopy. The fracture path was examined by observing the side surface in a partially ruptured specimen. The relationship of the fracture facets to the microstructures was established by observing the fracture surface and the adjacent side surface simultaneously. Three kinds of fracture facets were identified at either temperature. The first is a smoothly curved intergranular fracture facet with characteristic parallel lines on it. The second is a fairly planar facet formed by parting along an annealing twin boundary, a real {111} plane. There are three sets of parallel lines on the facet and the lines in different sets intersect at 60 deg. The third is a lamellar transgranular fracture facet with sets of parallel steps on it. Fracture propagated by the formation of microcracks on a grain boundary, annealing twin boundary, and coalescence of these cracks. The observation suggests that the ease of crack initiation and propagation along the grain boundary and the annealing twin boundary may be the main reason for the low-temperature brittleness of this steel. A mechanism for grain boundary cracking, including annealing twin boundary parting, has been discussed based on the stress concentration induced by impinging planar deformation structures on the grain boundaries.
29 citations