Steel Frame Welding Robot Systems and Their Application at the Construction Site

Two welding robot systems have been developed to rationalize steel–frame construction. Both systems consist essentially of two portable cartesian–coordinate welding robots mounted on a carriage together with their ancillaries. After the robots are mounted on a beam or column by an operator, they measure the groove shape of the joint seam, determine the optimal welding conditions, and carry out welding from the first to the last layer without operator intervention.
An important feature of the column–beam welding system is the curved torch, with which the robot can continuously weld the bottom flange of a beam through a scallop. Since the pantograph of the carriage can extend three floors, up to 12 joints can be welded from one carriage position.
In welding column–column joints, two robots traveling on a circumferential rail installed near the seam of a rectangular hollow section weld the joint in combination. The robots can continuously weld a seam containing corners without weld defects even in joints with a misaligned groove.
Each system has been applied to actual construction sites and has proved effective in stabilizing the quality of welds and in raising welding productivity.     

Deformation Structure Around a Crack in γ′-Fe4N Layer of Nitrided Extra-Low-Carbon Steel Subjected to Cyclic Tensile Test

Numerous slip bands were detected in the γ′ layer of nitrided steel subjected to cyclic tensile testing, indicating that γ′ can easily deform plastically under a low-applied stress (175 MPa). A crack arrested inside a γ′ grain propagated along the {100} and {111} planes, and planar dislocations were emitted from the crack tip. The stress concentration at the crack tip induced a cleavage fracture and slipping-off in the γ′, leading to a crack propagation.

     

Amorphous Si1−xCx:H films prepared by hot-wire CVD using SiH3CH3 and SiH4 mixture gas and its application to window layer for silicon thin film solar cells

B-doped hydrogenated amorphous silicon carbon (a-Si_1−xC_x:H) films have been prepared by hot-wire CVD (HWCVD) using SiH₃CH₃ as the carbon source gas. The optical bandgap energy and dark conductivity of the film are about 1.94 eV and 2 × 10^− 9 S/cm, respectively. Using this film as a window layer, we have demonstrated the fabrication of solar cells having a structure of the textured SnO₂(Asahi-U)/a-Si_1−xC_x:H(p)/a-Si_1−xC_x:H(buffer)/a-Si:H(i)/μc-Si:H(n)/Al. The conversion efficiency of the cell is found to be 7.0%.     

An applicability of dynamic response analysis of shear-failure type RC beams with lightweight aggregate concrete under falling-weight impact loading

In order to establish a simple and rational impact response analysis method for lightweight aggregate reinforced concrete (RC) beams, three-dimensional elasto-plastic finite element analysis was conducted for shear-failure type RC beams under falling-weight impact loading. The, tensile strength of concrete was assumed as 1/16th of the compressive one. An applicability of the proposed analysis method was confirmed by comparing with the experimental results of twelve beams. From this study, following results were obtained: (1) three response wave configurations: impact force; reaction force; and mid-span displacement, and crack patterns can be rationally predicted by using proposed analysis method; and (2) maximum response values of impact force, reaction force, and displacement can be estimated considering 20, 20, and 10% safety margin, respectively.     

Proposal for an engineering definition of a fatigue crack initiation unit for evaluating the fatigue limit on the basis of crystallographic analysis of pearlitic steel

In this study, in order to define a fatigue crack initiation unit, the relationship between the fatigue crack initiation process and the crystal structure in the pearlitic steel used for railroad rails was examined and fatigue tests, focusing on crack initiation, were performed. The fracture surfaces were analyzed using a scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The crystal structure of the pearlitic steel is composed of “pearlitic colonies” that have the same lamellar structure direction and “pearlitic blocks” that have the same ferrite crystal direction. The SEM and EBSD results revealed that the crack initiation depends on the pearlitic colonies. Therefore, we defined the characteristic dimension for fatigue crack initiation as the pearlitic colony size. However, for safety purposes, the pearlitic block size should be considered the engineering definition of the fatigue crack initiation unit, since decreasing the pearlitic block size should cause an improvement in the fatigue limit of pearlitic steel.     

Evaluation of the interfacial properties in the embedded-single-fibre coupon test

The embedded-single-fibre tension test is a very useful technique for the evaluation of interfacial properties in composite materials. There are, however, some problems with this method. A comparison is made between the normal embedded-single-fibre method characterized by critical fibre length and the interfacial transmissibility method proposed by the authors. The effects of resin properties, in particular, are discussed. As the results show, there is some difficulty in evaluating the interfacial properties by the normal embedded-single-fibre method in the case of brittle-matrix systems, whereas interfacial transmissibility provides the possibility of evaluating interfacial properties over a wide range of resin properties.     

An application of impact-response analysis on small-scale RC arch-type beams without stirrups

To establish a rational impact response simulation method for arch-shape RC beams, the applicability must be confirmed by conducting falling weight impact loading tests of small-scale arch-shape RC beams. However it is not easy to conduct the experiments because of preparing of specimens and fitting of experimental setup. Numerical simulation method may be one good choice, if the accuracy is guaranteed. Because, now a days, impact response analysis for RC members can be performed by using computers. In this paper the applicability of impact response simulation method for arch-shape RC beams has been discussed by comparisons with experimental results. From this study, the following results are obtained: (1) the impact force time history, maximum displacement at the loading point and crack patterns caused in the side-surface of the arch beams can be simulated, which are in good agreement with the experimental results; however, (2) the damped free response after unloading and residual displacement cannot be better simulated.     

Reversible transformation and fluorescence modulation in polymorphic crystals of n-butylammonium 2-naphthalenesulfonate

An organic salt composed of 2-naphthalenesulfonic acid and n-butylamine yielded polymorphic crystals: the block-like Form A and the plate-like Form B. The former was obtained from 1-propanol by slow cooling, while the latter was dominantly done from 1,4-dioxane, m-xylene and so on. Interestingly, the former was transformed to the latter by mechanical grinding and the reverse occurred by heat treatment at 120 °C. X-ray crystallographic studies clarified that the former has π–π interactions among naphthalene rings and hydrogen bonding network involving two oxygen atoms of sulfonate group, while the latter has CH–π interactions and the network involving three oxygen atoms. Luminescent properties were different in these crystals and continuously switched with the transformation.     

Role of ferrite and austenite phases on the deformation behavior and mechanical properties in heterogeneous nanostructured duplex stainless steel aged at different temperatures

Journal of Materials Science - The effects of aging on the mechanical properties of a heavily cold-rolled ferrite–austenite duplex stainless steel were systematically investigated. The...