For a crack in a metal to expand under the influence of the stretching forces, it is necessary to spend some work on the plastic deformation’ flowing along the forming crack’ borders and on the forming of new surfaces. D. Irwin and E. Orowan proposed to introduce the value of G that would express the plastic deformation’ work at the crack’s mouth with its advancement at the moment of the motion start expressed in a unit of length. The G value can be expressed as a unit of force per a Continue reading →
Generation of crystals in liquid (Part 4).
To a large extent, the process of generation is affected by the inclusion surface’ topography. If there are depressions on the surface, the critical dimension nucleus’ size and the work required for its formation are smaller than those for the flat surface. The influence that the nonisomorphic impurities exert on the process of crystal formation can be boosted if they have previously been in contact with the crystals of the given substance. At the temperatures that are not too low, under the influence of the crystal’s atoms, the structure of the impurity inclusion’ surface Continue reading →
Certification of welders (Part 1).
Certification results of welding technology obtain practical value only after certification of individual welders for executing welding works in compliance with this technology. These two types of measures differ from each other in virtue of different goals of their existence. We will presume that suitable welding technologies were accepted and confirmed with the help of one or other method. To determine if the welders have enough qualification for executing qualitative Continue reading →
Pores in welded seam (Part 2).
Tunnel pores represent one more type of extended pores. Usually tunnel pores with formation of contraction cavity represent the most dangerous defect in the case, if main designation of welded seam is in retaining gas or liquid; since at that exists the big possibility of leakage path formation.
Tensile tests (PART 6).
When conducting tensile tests the beginning of yield point is marked with decreasing of apparatus values or recording device. Yield point can be determined by observing and registration these type of stress decreasing. This method is called method of testing machine lever dropping, which indicates that subject sample reached elasticity limit.