Final answer:
The three broad classes of weld discontinuities are surface defects, volumetric defects, and structural defects, each affecting the integrity and performance of welded components.
Step-by-step explanation:
The three broad classes of weld discontinuities are surface defects, volumetric defects, and structural defects. Surface defects are discontinuities that appear on the surface of the weld, such as cracks or excessive porosity. Volumetric defects are anomalies that occur within the volume of the weld, like inclusions or improper fusion. Structural defects refer to deviations from the intended weld geometry or the presence of unwanted stresses within the welded joint that may lead to its failure. These types of discontinuities can have significant impacts on the integrity and performance of welded structures.
Surface Defects
Surface defects arise at the grain boundaries, where the properties are different compared to the internal grains. Chemical etching can reveal these defects, which include vacancies, interstitial atoms, and substitution impurities.
Volumetric Defects
Volumetric defects occur within the material and can involve point defects like Frenkel and Schottky defects, often found in ionic crystals.
Structural Defects
Structural defects influence the mechanical properties of materials and include line defects, which weaken the structure along a one-dimensional space, and plane defects, which occur along two-dimensional surfaces.