YIELD STRESS UNDER REPEATED LOADING AFTER APPLYING DIFFERENT DEFORMATION PATH FOR LARGE TENSION AND SHEAR

This paper describes the yield phenomenon when a repeated loading is applied to the structure after giving a large pre-strain on it. In the series of our previous research, focusing on the fundamental deformations such as tension or shear, changes of yield stress as the number of repetition increases have been investigated experimentally by using test specimens of annealed pure copper. In the determination of yield stress value, the method by using slope of stress-strain curve at yield has been used instead of proof stress. As a consequence, it has been found that if the type of pre-deformation and the type of deformation in repeated load are the same, yield stress at the pre-deformation side has a declining tendency as compared with opposite side. Therefore, it is predicted that the yield stress under repeated loading after applying a large deformation is closely related to the loading history in large deformation previously applied. Thus, in this study, in order to clarify the influence of pre-deformation on the yield behavior under repeated loading, the experiments are performed by changing the order of tension and shear in pre-deformation. Consequentially, it is clarified that the declining tendency of yield stress under repeated loading is closely related to the yield surface anisotropy, which is formed during the second half of the pre-deformation.

Tailoring Microstructure and Mechanical Properties of Additively-Manufactured Ti6Al4V Using Post Processing

Additively-manufactured Ti-6Al-4V (Ti64) exhibits high strength but in some cases inferior elongation to those of conventionally manufactured materials. Post-processing of additively manufactured Ti64 components is investigated to modify the mechanical properties for specific applications while still utilizing the benefits of the additive manufacturing process. The mechanical properties and fatigue resistance of Ti64 samples made by electron beam melting were tested in the as-built state. Several heat treatments (up to 1000 °C) were performed to study their effect on the microstructure and mechanical properties. Phase content during heating was tested with high reliability by neutron diffraction at Los Alamos National Laboratory. Two different hot isostatic pressings (HIP) cycles were tested, one at low temperature (780 °C), the other is at the standard temperature (920 °C). The results show that lowering the HIP holding temperature retains the fine microstructure (~1% β phase) and the 0.2% proof stress of the as-built samples (1038 MPa), but gives rise to higher elongation (~14%) and better fatigue life. The material subjected to a higher HIP temperature had a coarser microstructure, more residual β phase (~2% difference), displayed slightly lower Vickers hardness (~15 HV10N), 0.2% proof stress (~60 MPa) and ultimate stresses (~40 MPa) than the material HIP’ed at 780 °C, but had superior elongation (~6%) and fatigue resistance. Heat treatment at 1000 °C entirely altered the microstructure (~7% β phase), yield elongation of 13.7% but decrease the 0.2% proof-stress to 927 MPa. The results of the HIP at 780 °C imply it would be beneficial to lower the standard ASTM HIP temperature for Ti6Al4V additively manufactured by electron beam melting.

Mechanical Properties of Laser-Sintered 3D-Printed Cobalt Chromium and Soft-Milled Cobalt Chromium

Purpose: To compare the mechanical properties and fracture behaviour of laser-sintered/3D-printed cobalt chromium (LS CoCr) with soft-milled cobalt chromium (SM CoCr) to assess their suitability for use in high-stress areas in the oral cavity. Material and Method: Two computer-aided manufacturing methods were used to fabricate dumbbell specimens in accordance with the ASTM standard E8. Specimens were fractured using tensile testing and elastic modulus, and proof stress and ultimate tensile strength were calculated. Fracture surfaces were examined using scanning electron microscopy. Plate specimens were also fabricated for the examination of hardness and elastic modulus using nanoindentation. Unpaired t-test was used to evaluate statistical significance. Results: LS CoCr specimens were found to have significantly higher ultimate tensile strength (UTS) and proof stress (PS) (p < 0.05) but not a significantly higher elastic modulus (p > 0.05). Examination of the dumbbell fracture surfaces showed uniform structure for the LS CoCr specimens whilst the SM CoCr specimens were perforated with porosities; neither showed an obvious point of fracture. Nanoindentation also showed that LS CoCr specimens possessed higher hardness compared with SM CoCr specimens. Conclusion: LS CoCr and SM CoCr specimens were both found to exhibit uniformly dense structure; although porosities were noted in the SM CoCr specimens. LS CoCr specimens were found to have superior tensile properties, likely due to lack of porosities, however both had mean values higher than those reported in the literature for cast CoCr. Uniformity of structure and high tensile strength indicates that LS CoCr and SM CoCr fabricated alloys are suitable for long-span metallic frameworks for use in the field of prosthodontics.

Use of Orthogonal Arrays in Design of a Fuzzy Logic Controller to Predict the Proof Stress for the TIG Welded Al-65032

Fuzzy logic controller (FLC) is well suited where there is a considerable amount of uncertainty in the process. The material properties of a weldment in TIG welding depend on welding parameters like shielding gas pressure, current, torch angle, Electrode size, electrode projection, arc length etc. It is also influenced by the joint parameters like groove angle, land, root gap, preheating temperature. But a lot of noise parameters like variation of base material properties, variation in quality of inert gas used, variation in ambient conditions, variation in workman ship etc introduce uncertainties in the into the process. To deal with such uncertainties an FLC is designed and validated. In the current work, four parameters namely inert gas pressure, current, groove angle of the joint and preheating temperature of base metal are considered as input variables and the influence of these variables on the 0.2% proof stress is studied. Three linguistic terms are used for each parameter. To minimise the number of experiments in designing data base an L-9 orthogonal array is chosen for experimentation. TIG welding is carried and data base with 9 rules are formulated. For the input and out variables Triangular membership function is selected and FLC is designed. The FLC is validated with 5 more experiments. Mamdani approach is used to develop the Fuzzy controller.

Study on improvement of strength of Beam-column Joints at railway RC rigid-framed viaducts

<p>In Japan, in order to make the city centering around the station, we are developing the underpass of the station as a commercial facility. Therefore, a structure that enlarges the column span and reduces the cross-sectional height of the beam to widen the under-elevated space is desired. However, while the amount of reinforcing bars increases, the beam-column joints become smaller, so that the reinforcing bars are overcrowded in the beam column joints. In addition, since the fixing length of the reinforcing bars is insufficient, or the strength of the beam-column joint cannot be sufficiently secured, problems such as not having a sufficient proof stress on the joint portion which should originally be stronger than the beam and column member. In this report, we developed a fixing method of reinforcing bars of column beams which improves the proof strength of beam-column joint and also simple reinforcing bars even in the case of small beam-column joint, and applied to station construction work, we report on them.</p>

Tensile and Fatigue Properties of Miniature Size Specimen of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge Lead-Free Solder

Tensile and low cycle fatigue properties of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) lead-free solder were investigated using miniature size specimens and obtained data were compared to those of Sn-3.0Ag-0.5Cu (mass%). The microstructure of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge consists of dendritic β-Sn phases and ternary eutectic phases surrounding them which are composed of β-Sn, (Cu,Ni)6Sn5 and Ag3Sn. Tensile strength and 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are superior to those of Sn-3.0Ag-0.5Cu at 25°C and 150°C. However, elongation of it is inferior to that of Sn-3.0Ag-0.5Cu at both temperatures. Fatigue lives of both alloys obey the Manson-Coffin equation and are analogous at 25°C. Although fatigue lives of both alloys decrease at 150°C, the fatigue life of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is inferior to that of Sn-3.0Ag-0.5Cu. At 150°C, the crack mainly progresses at grain boundaries of recrystallized grains. Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge has several grain boundaies which can be the origin of the crack so that fatigue lives degrade at 150°C.

Microstructural Characterization of Mg-TM (TM=Ni or Cu) - Y Alloys and their Mechanical Property

Microstructure and mechanical property of the Mg-TM (TM=Ni or Cu) -Y alloys were investigated. Results revealed that Mg phase, Long period stacking ordered (LPSO) phase, and Mg2TM phase were formed in the Mg-TM-Y alloy around the composition ratios of TM and Y are 1:1 or 1:2. Tensile test clearly showed relationship between the mechanical property and microstructure in Mg-Ni-Y cast alloy. The 0.2% proof stress (σ0.2) of the Mg-Ni-Y cast alloy increase with the increasing solute elements contents, while the elongation decreases. This result indicated that the Mg-TM-Y alloy with the composition ratios of TM and Y are 1:1 or 1:2 have both high proof stress and appropriate elongation. It was suggested that the LPSO phase was appropriate strengthening phase in the Mg-rich region in the Mg-TM-Y alloy system. Basal texture of the LPSO and Mg phases was formed by hot-rolling in the sheet plane and the Mg2TM phase was dispersed in the Mg phase. The Mg97Cu1Y2 rolled sheet showed highσ0.2 about 350 MPa at room temperature. Furthermore, formation of an oxide film on the Mg-Cu-Y alloy was investigated at 973 K in air. As a result, it was suggested that the Y2O3 film was formed on the re-melted Mg-Cu-Y alloy surface as an incombustible oxide film.

Comparison of Sn-5Sb and Sn-10Sb Alloys in Tensile and Fatigue Properties Using Miniature Size Specimens

Tensile and low cycle fatigue properties of Sn-5Sb (mass%) and Sn-10Sb (mass%) were investigated using miniature size specimens, and fracture behaviors of the specimens were observed. Tensile strength and 0.1% proof stress of both alloys decrease with increasing the temperature. The tensile strength and 0.1% proof stress of Sn-10Sb are higher than those of Sn-5Sb at 25°C. Elongation of Sn-5Sb decreases with increasing the temperature except for a strain rate of 2 × 10−1 s−1, while Sn-10Sb increases with increasing temperature. Although elongation of Sn-10Sb is lower than that of Sn-5Sb at 25°C, the difference between them is small at 150°C. Chisel-point fracture was observed in both alloys regardless of conditions of the tensile test. The low cycle fatigue lives of Sn-5Sb and Sn-10Sb alloys obey the Manson–Coffin equation, and the fatigue ductility exponent, α, was 0.54 for Sn-5Sb and 0.46 for Sn-10Sb in the temperature range from 25°C to 150°C. On the basis of the observation of fractured specimens and the investigation of α, it was clarified that the crack progress can be delayed by the formation of coarse SbSn compounds in the Sn-Sb alloy, and thus the fatigue properties can be improved.