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A prospective study was undertaken to assess the value of both T2-weighted spin-echo (SE) and contrast-enhanced dynamic gradient-echo (GRE) sequences using MR imaging in differentiating the deep myometrial invasion from lower stages produced by endometrial carcinoma. For the correlation of MR findings with the histopathologic findings, patients who had no myometrial invasion (stage 1 a) and patients in whom tumors were confined to the superficial myometrium (stage 1 b) at pathologic examination were combined as lower stages. Twenty patients with endometrial carcinoma were studied using both techniques. The absence of any detectable tumor (stage 1 a) or the presence of a tumor confined to inner half of myometrium (stage 1 b) and extention of tumor to the outer half of myometrium (stage 1 c) were used as the diagnostic criteria. In pathologic examination of excised specimens, deep myometrial invasion was detected in 9 of 20 patients. The sensitivity, specificity, accuracy, positive predictive values (PPV) and negative predictive values (NPV) of T2-weighted SE in differentiating deep myometrial invasion from combined lower stages were 88, 91, 90, 88, and 91 %, respectively, whereas corresponding values for contrast-enhanced dynamic GRE sequences were 78, 100, 90, 100, and 85 %. Statistical difference between two sequences did not reach a significant level. We conclude that in cases of absence of visible junctional zone with SE sequence, contrast-enhanced dynamic GRE MR imaging may be helpful.

Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials behave when they are welded. This paper presents the process parameters' optimization procedure of fiber laser welded dissimilar high strength low alloy (HSLA) and martensitic steel (MART) steel using a Taguchi approach. The influence of laser power, welding speed and focal position on the mechanical and microstructural properties of the joints was determined. The optimum parameters for the maximum tensile load-minimum heat input were predicted, and the individual significance of parameters on the response was evaluated by ANOVA results. The optimum levels of the process parameters were defined. Furthermore, microstructural examination and microhardness measurements of the selected welds were conducted. The samples of the dissimilar joints showed a remarkable microstructural change from nearly fully martensitic in the weld bead to the unchanged microstructure in the base metals. The heat affected zone (HAZ) region of joints was divided into five subzones. The fusion zone resulted in an important hardness increase, but the formation of a soft zone in the HAZ region.

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Abstract:In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy-electron back-scattered diffraction (SEM-EBSD), microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ), coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL) commonly exhibited more brittle fracture characteristics.

AA6082-T6 alloy was joined by friction stir spot welding using five different pin profiles, such as a cylindrical, conical, triangular, hexagonal and cylindrical with two grooves, at different dwell time. The joints welded by cylindrical pins had larger effective weld width. But, grooves on the cylindrical pin decreased the effective weld width. The hook was bent downward from the interface of the sheets in the weld made with hexagonal pin, which had the smallest effective weld width. When conical pin was used, effective weld width increased with increasing the dwell time. In the case of using tools with cylindrical and conical pins, HAZ hardness was relatively lower. With increasing dwell time, HAZ hardness of the joints made with conical pin decreased. Effective weld width determined the weld strength under the tensile shear loading condition: Larger effective weld width resulted in higher weld strength. Weld strength of the joints made with cylindrical pin was higher. The joints fabricated with hexagonal pin had the lowest weld strength. In general, higher dwell time led to higher weld strength. The welds with the higher strength experienced both brittle and ductile fractures, while the joints with the lower strength exhibited completely brittle fracture.

In this study, the effect of microstructure on the mechanical properties of four types of ductile cast irons with different morphologies was investigated using circumferentially notched cylindrical specimens with different notch root radii. These cast irons were also austempered using the same austempering heat treatment to make a comparison with the as-cast samples. Characterization of the specimens has been carried out by means of microstructure, hardness, tensile properties, notch tensile strength, notch sensitivity, fracture toughness, and fractography. A mixture of ferrite and pearlite in the microstructure of cast irons gives rise to a material of the highest tensile strength, notch tensile strength, and fracture toughness properties with the intermediate ductility and notch sensitivity. A higher pearlite in the matrix of cast irons gives very important mechanical properties such as hardness and strength, but brittleness of the matrix andnotch sensitivity are greatly increased. Austempering significantly increased the mechanical properties and also reduced the difference between the mechanical properties of the cast irons. Austempered ferritic ductile irons exhibited the highest notch tensile strength and fracture toughness, and the high tensile strength and the intermediate ductility properties with the lowest notch sensitivity, whereas austempered pearlitic ductile irons had the lowest tensile strength, ductility, notch tensile strength, fracture toughness, and the intermediate notch sensitivity properties. The mechanical properties of the as-cast and austempered ductile irons have increased almost linearly with increase in the notch root radius.

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