Notch effect describes how geometry itself concentrates stress. When there’s an abrupt change in section thickness or continuity, the load path is disrupted and the local stress rises above the nominal value, creating a hotspot where cracks can initiate. That geometric-driven concentration is exactly what the term notch effect captures. Residual stress is a separate idea: it’s the internal stress locked into a material after processing or welding and cooling, present even without any external load. It can influence how a notch behaves, but it isn’t the description of the concentration caused by the geometry itself. Buckling is a stability failure under compression, and arc blow is the welding arc wandering due to magnetic effects—neither describes the notch-driven stress concentration.

Heat input rises with the current needed to melt the filler metal. A larger diameter filler rod requires more current to melt and deposit it at the same rate, so the arc delivers more energy into the weld per unit length. That extra energy widens the heat-affected zone and increases thermal distortion in the welded part. Therefore, larger diameter filler metal increases heat input and distortion. The other statements don’t fit the practical relationship: using a larger diameter filler doesn’t reduce heat input, filler diameter does influence heat input because it changes the current required, and while a smaller diameter can require less heat, the statement about it universally reducing heat input and distortion isn’t as accurate as describing the direct effect of a larger diameter increasing heat input.

In a multi-pass GTAW butt weld, the root pass establishes fusion and penetration at the joint root. It is the first layer that fuses the two base metals together at the bottom of the joint, creating a continuous weld through the joint depth. This solid foundation lets subsequent passes fill and cap the weld reliably. If the root doesn’t properly fuse and penetrate, you can end up with weak root fusion or lack of fusion at the base of the weld, even if later passes are added. Finishing the surface, filling to full height, or applying final texture are tasks for later passes and finishing steps, not the root itself.

In GTAW, you use a nonconsumable tungsten electrode to establish the arc while filler metal is added separately. Occasionally, tiny particles of tungsten can shed from the electrode and get carried into the molten weld pool, becoming trapped as the weld cools. These are solid inclusions, distinct from porosity (gas pockets) and from filler metal, which is added separately. So the statement is correct: tungsten inclusions are particles from a nonconsumable tungsten electrode that enter the weld. Preventive steps include keeping the electrode clean, avoiding contact with the work and using proper amperage and technique to minimize electrode wear.