Itsuro Tatsukawa

MEASUREMENT OF TRANSIENT STRAIN DURING WELDING BY GRID PATTERNS.

The present study proposes a measurement of transient welding strains in areas near weld . In the measurement technique, grid patterns previously photo-etched on surface of a plate are photographed progressively during welding; after welding, each grid distance at every moment is observed with the photographic film using micro-photometer, from which total strain is determined. Experiments are conducted to examine the accuracy of the measurement and the mechanism of radial and circumferential strains in aluminum alloy thin plate heated by gas tungsten arc. Moreover, the plastically deformed zone in the plate is sized from the two-dimensional total strain values by a mathematical equation based on the theory of elasticity and plasticity. The main results are as follows. The photographic recording method reveals precisely the total strain distribution which shows the individual change according to the plastic deformation occurring around the molten zone and the cooling effect of shielding gas as well as the thermal expansion of the plate. The size of plastic zone calculated from the total strain values after heating is reasonably close to that experimentally observed by stress re laxation. The size spreads at early stage of the heating with additional deformation in the thickness direc tion and increases with increasing heat input.

Fracture Toughness of Explosive Stainless-Clad HT80 High Strength Steel

Fracture toughness of explosive clad composed of SUS 304 stainless steel and HT80 high strength steel is investigated. To clarify the effect of metallurgical properties and composite structures on the fracture toughness, both V-notch Charpy test and bending COD test are carried out by using homogeneous and heterogenous specimens which are cut from various portions in thickness direction of the clad plate and have notch root or precrack leading edge parallel to the plate surface. The energy absorbed for fracturing the specimens and its component energy for crack initiation from notch root in V-notch Charpy test are affected by the material involving notch root and by the thickness ratio of two different steels in net section of specimen.In static bending test of the heterogeneous specimens with pre-crack tip in stainless steel, fracture occurs in the high strength steel adjacent to weld interface before the pre-crack extends although ductile fracture occurs at pre-crack tip over all temperature range. In relation to crack initiation, the critical COD, if the first fracture initiation in interface zone can be measured, and the stretched zone width, if fracture firstly occurs at pre-crack tip, can be a parameter of fracture toughness respectively.In the heterogeneous specimens with pre-crack tip in high strength steel, both the critical COD at low temperature where ductile fracture has not yet initiated and the stretched zone width over all tem-perature range can be fracture toughness parameters since the fracture toughness values depend largely on the material involving pre-crack tip, namely, high strength stecl.

Strain Characteristics in Submerged Arc Welding of Mild Steel

As a basic research of strain characteristics in automatic arc welding process, which is executed in considerably higher arc current and welding speed than those of manual arc welding, the investigation has been experimentally carried out on submerged arc welding of mild steel plate under different heat inputs (Fig.1 and Table 2). Detailed observation covers the welding thermal cycles, the progress of longitudinal and transverse strains in base metal during welding and cooling as well as the distributions of the longitudinal total, elastic and plastic strains, the transverse shrinkage and the angular distortion after welding. Main results obtained are as follows.The transient mechanical strains of longitudinal and transverse directions occur respectively in tension and compression conversely to each other during the former stage of welding and, afterward, change into compression and tension according to the thermal expansion and shrinkage of the weld zone, which are inferable from the thermal cycles (Figs.3 and 8).From the distributions of longitudinal total strain and transverse shrinkage after welding, it is clear that the welded plate expands longitudinally in its middle and contracts in its outer portions, that is, the half of plate on either side of the weld line deforms into fan-shape, these rotational deformation being re-markable in case of large heat input (Figs.5 and 10). And also, the large heat input reduces the magnitudes of longitudinal plastic shrinkage occurring in the weld zone, extends transversely the region of its occurrence and consequently reduces the inherent shrinkage (Figs.11 and 12). The observed distributions of longi-tudinal residual stress and plastic strain along the transverse center line of welded plate, in case of low heat input, well agree with those theoretically derived (Tables 4 and 5).