Abstract: In order to evaluate the mechanical properties of steel, empirical equations showing the relationship between each of the tensile strength, yield point and elongation of steel and its hardness, grain size and chemical composition are determined in advance based on experimental results. Then, the hardness, grain size and chemical composition of the steel to be evaluated are determined. The tensile strength, yield point and elongation of the steel to be evaluated are determined by inserting the determined hardness, grain size and chemical composition in the empirical equations. In determining the energy absorbed according to a method of this invention, empirical equations showing the relationship between each of the shelf energy, transition temperature and temperature range of the energy transition region of steel and its hardness, grain size and chemical composition are determined in advance. Then, the hardness, grain size and chemical composition of the steel to be evaluated are determined.

Abstract: A structure fastening cable has a strand of a large number of metal element wires and a corrosion-preventive layer. The cable also has a cylindrical conductive resistance detector that extends inside and over the entire length of the cable in such a manner as to surround the strand with an insulating layer in between and a device to measure the resistance of a circuit composed of the strand, resistance detector and insulating layer. The resistance detector consists of a cylinder element of metal sheet or spirally wound metal ribbon. The measuring device is inserted in a circuit that connects an end of the strand to an end of the resistance detector at one end of the cable. When the corrosion-preventive layer breaks, seawater enters the reaches the peripheral surface of the strand to establish an electrical connection between the strand and resistance detector via the penetrated seawater, with a resulting sharp reduction in the resistance between the strand and resistance detector.

Abstract: A high-frequency electric resistance welding method combined with the irradiation of a laser beam in which a workpiece is continuously fed and opposed edges of the workpiece are formed into a wedge shape by causing them to converge as they are butted against each other, and the butted edges are melted by heating them with high-frequency resistance heating and a laser beam, to weld the butted edges. The laser beam is projected against the range of over 30% and below 80% of the thickness of the butted edges including the central portion of the thickness to melt the butted edges by the combined heating action of the laser beam and high-frequency current. The corners are heated and melted by means of high-frequency electric resistance heating, so that the butted edges of the workpiece can be melted uniformly through the entire range of thickness.

Abstract: Conventional beam-welding methods have disadvantages in that the total energy efficiency is low and that the bonding zone and HAZ spread due to indirect heating of the weld zone. In the present invention, a wedge-shaped space is formed between the non-contact parts of the articles, and an energy beam, such as a laser beam, an ion beam, and a plasma arc, is projected into the wedge-shaped space so as to heat the weld zone or the parts of articles which will later be joined. The controlling apparatus of the present invention controls the power of, for example, a laser beam based on the detecting of travelling speed of sheets and the like.

Abstract: The grain size is expressed by the diameter of grains demarcated at high-angle grain boundaries, such as ferrite grains in ferritic steels. Ultrasonic waves having a frequency f are propagated through an object to be examined and its attenuation constant .alpha. is determined. Using the ratio f/.alpha. and equationC'.sub.j .ltoreq.f/.alpha..ltoreq.C'.sub.j+lwhere C'.sub.j and C'.sub.j+l are constants and j is a constant between 1 and 4, the order j of the region to which the value of f/.alpha. belongs is determined. Then the grain diameter D is derived from equation ##EQU1## using an integer n.sub.j and constant A.sub.j predetermined for the order j of each region.

Abstract: Conventional beam-welding methods have disadvantages in that the total energy efficiency is low and that the bonding zone and HAZ spread due to indirect heating of the weld zone. In the present invention, a wedge-shaped space is formed between the non-contact parts of the articles, and an energy beam, such as a laser beam, an ion beam, and a plasma arc, is projected into the wedge-shaped space so as to heat the weld zone or the parts of articles which will later be joined. The controlling apparatus of the present invention controls the power of, for example, a laser beam based on the detecting of travelling speed of sheets and the like.