Papers by Keyword: Fracture Surface

Abstract: Three CT specimens from stainless steel AISI 304L were subjected to constant amplitude cyclic loadings with various asymmetries. Crack growth was recorded in detail. Fracture surfaces were documented by 3D maps in about 110 locations in the crack growth direction. 3D maps and their local gradients were represented by 2D wavelet decompositions in 10 levels resulting in 60 textural features. Statistical models expressing crack growth rate as a function of textural features were optimized. Training and testing approach, a high ratio of overfitting, and testing of significance of components ensured model's robustness. Quality of results is documented by graphs confronting model outputs with real data known from experiment. Results are acceptable in all cases.

Abstract: The paper presents comparison of microstructure and fracture surface morphology of the CuAlNi shape memory alloy (SMA) after different heat treatment procedures. The investigation was performed on samples in as-cast state and heat treated states (solution annealing at temperatures of 850 °C / 60’ / H₂O and 920 °C / 60’ / H₂O along with tempering at two different temperature 150 °C / 60’ / H₂O and 300 °C / 60’ / H₂O). The microstructure of the samples was examined by optical (OM) and scanning electron microscope (SEM) equipped with device for EDS analysis. The obtained fracture surfaces were examined by SEM. Optical and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the fractographic analysis of samples after tensile testing reveals significant changes in fracture mechanism. In both solution annealed states the results shows transgranular type of fracture, but after tempering at two different temperatures the difference is obvious. After tempering at 150 °C, along with transgranular type of fracture appear some areas with intergranular type of fracture. After tempering at 300 °C, fracture surface reveals completely intergranular type of fracture.

Abstract: Low carbon steel is one of the most common steels used in industry because of its low cost. If more strength is required, it can be strengthened by induction heating which is also a low-cost method. In order to investigate the effect of induction heating on large diameter shafts, we performed rolling bending fatigue tests using 10 mm diameter specimens. We found that TRO cracks originating from the boundary between the soft and hard layers governed the fatigue fracture of the shafts.

Abstract: Produced Profiles by direct recycling of aluminum chips in hot extrusion process were achieved by temperature related parameters using preheating temperature 450 °C, 500 °C, and 550 °C for duration 1 hour, 2 hours, and 3 hours preheating time. By using Design of Experiments (DOE) procedure with full factorial design and three center points analysis, the results showed that the preheating temperature factor is more important to be controlled rather than the preheating duration and increase of temperature conducted to the high tensile strength. The profiles extruded at 550 °C and 3 hours’ duration had obtained the optimum condition to get the maximum tensile strength. The influence of parameters of hot extrusion process on fracture surfaces of the recycled samples was also investigated and discussed.

Abstract: High-carbon high-strength JIS-SUJ2 bearing steel is one of the alloys used as rolling contact applications which need high wear resistance. This high hardness material is broken from non-metallic inclusions under fatigue stress. In this work, we developed a new observation method “fracture surface etching (FSE)” in order to observe the material microstructure on the fracture surface. We succeeded to draw clear grain boundaries on the fracture surfaces and closely observed the material microstructure around the crack origins by the FSE method. We concluded that the crack initiation area boundary is not formed by only the grain boundary, and the grain size around the Al2O3 inclusion on the fracture surface was similar to that of the flat surface which does not have inclusions before fatigue testing.

Abstract: It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σ_a) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σ_a =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.

Abstract: In tri-layered Cold Roll Bonded (CRB) composite sheets of dissimilar metals, uneven thickness reduction of the different layers have been observed. This has been explained by the difference in yield strength/flow stress of the metals. The aim of this research was to study if these observations also depend on different parameters such as stacking sequence and initial sheet thickness, as opposed to only material properties. Hence, tri-layered CRB composite sheets consisting of AA6082 and IF-steel were produced with two different stacking sequences, St/Al/St vs Al/St/Al. Two different layer thicknesses of the intermediate layer were used. Rolling was performed in a single pass achieving approximately 55-65% total thickness reduction. Comparisons between the samples are given, focusing on the reduction of thickness achieved in each layer, the roll bonded interface characteristics and the bond strength of the joints. The overall thickness reduction achieved in each layer was found to be similar for both metals in both stacking sequences for the considered material combination. The stacking sequence is statistically found not to have any effect on the bond strength of the joints. The thickness of the intermediate layer does not significantly affect the overall bond strength of the composite sheet for both stacking sequences. These findings are opposed to earlier results found in the literature.

Abstract: The article shows the analysis of castings parts produced by rheocasting method SEED. Structures of as cast and heat treated castings samples were observed by light microscopy and electron microscopy. Scanning electron microscope was also used for studying of fracture surfaces after destruction of the samples during testing of mechanical properties. Also analysis of chemical composition of specific phenomena found within the structure is described. Findings resulting from those analyses are related with the technological settings and other process conditions.

Abstract: The effect of In addition to Zn-5Al on the interfacial reaction behaviors and mechanical properties of solder joints were investigated. It was found that addition of In decreasing the melting point of Zn-5Al solder. The segregation of In on grain boundary was observed. CuZn5 and Cu5Zn8 intermetallic phases were observed at joint interface. Segregation of In on grain boundary caused a significant decrease of strength of the Zn-5Al-In solder compared to Zn-5Al. Addition of 1% In to Zn-5Al solder resulted in a reduction of shear strength of 14 MPa. The interfacial microstructure, shear strength and fracture surfaces of Zn-5Al/Cu and Zn-5Al-1In/Cu solder joints were studied.

Abstract: A high pressure die cast Mg-9%Al-1%Zn alloy was friction stir processed at two high rotation rates and advancing speeds. Tensile tests were performed at higher temperature to study the mechanical properties of the microstructure induced by the friction stir process. Fracture surfaces resulting from tensile tests were observed by scanning electron microscopy and investigated by microanalysis. The fracture occurred in the tmaz and inside the stirring zone, depending on deformation conditions (temperature and strain rate). The morphology of the fracture surface varied from ductile to brittle in the same sample depending on phase type. Microhardness was measured on cross sections perpendicular to the advancing direction of the stirring pin, at various depth levels, before performing tensile tests to estimate the attitude of a single region to be deformed.