The toe of the weld is often the "weakest link" in a weld. This is due mainly to geometry and subsequent stress concentrations.
Abstract. Weld seam is the weakest point of the structure. Weld defects, weld geometry such as toe radius, and residual stresses, which are typically tensile in the critical area, weaken the fatigue strength of the weld seam.
The fillet welds are subjected to tensile stress. The minimum cross-section of the fillet is at the throat. Therefore the failure due to tensile stress occurs at the throat section. Thus the weakest area of the weld is the throat.
Service failures of welds, similar to those of any other structural component, depend on the operating environment and the nature of the applied load and may include failures from: Overload failure by brittle cracking mechanisms. Overload failure by ductile cracking mechanisms. Plastic collapse.
Any imperfections in the metals being joined together can result in joint failure. For instance, parts that were exposed to high heat might have distortions that make it harder for welders to achieve proper alignment. On the bright side, these issues are easily identifiable even before striking the arc.
The overhead position is the most challenging welding position, as gravity can cause the weld metal and slag to fall out of the joint.
Misalignment occurs in butt joints if the central lines of the two plates are not fully parallel (small-angle misalignment), or if a small shift between these lines is present. A tension load on the joint then introduces plate bending at the weld which can significantly impair the fatigue strength.
Welded joints are more brittle and therefore their fatigue strength is less than the members joined. Due to uneven heating & cooling of the members during the welding, the members may distort resulting in additional stresses. Skilled labor and electricity are required for welding.
Many different factors can cause weld quality issues: Low Weld Current - if sufficient temperatures aren't reached, the two metals may not be fused and the weld may fail. Poor Electrical Connection - loose cables or connections, contaminants, or oxidization can impede current flow, causing the weld to fail.
∴ For fillet weld, the weakest plane is along the throat section.
Scanning contact potentiometry (SCP) is a nondestructive method used for defects detection, and for determining the location coordinates of defects in welded joints.
The strength of the weld joint depends on either tensile or shear stress, or a combination of both. The direction of the weld joints decides the design stress (see stress calculator for more) acting on them.
A fillet weld can be loaded in any direction in shear, compression, or tension. However, it always fails in shear.
TIG welding is often considered the strongest weld since it produces extreme heat, and the slow cooling rate results in high tensile strength and ductility. MIG is also an excellent candidate for the strongest type of weld because it can create a strong joint.
Welded joints are normally stronger than bolted joints, in great part because their material does not have the perforations needed for bolted joints.
However, despite of this, welded joints can also represent the weakest part of structures and are susceptible to failure. The quality and strength of welded joints depend on factors such as the design, dimensioning and welding processes undertaken during fabrication.
TIG welding is the hardest form of welding to learn for a variety of reasons. The process of TIG welding is slow and takes time to get used to as a beginner. A TIG welder requires a foot pedal to feed the electrode and control the variable amperage while maintaining a steady hand at the welding torch.
Flat Welding Position
Also known as the downhand position, the flat position is the easiest of all the welding positions. A flat position is the common type of weld. It is the first weld that beginners learn. In this position, you are not welding against gravity.
Welds with a 1 are flat position, 2 is horizontal, 3 is vertical and 4 is overhead. F stands for fillet weld, while G is a groove weld.
#1 Flat position
The flat position is also called the down-hand position. It is most of the time the easiest and best position to weld with. In the flat position, the workpiece is flat and your welding electrode moves in a horizontal direction. In the flat welding position you weld on the top side of your workpiece.
The sign of a quality and secure weld is that you will not see the weld at all. If there is any visible evidence of a weld, it will be in the form of a bead that has no holes or cracks and is uniform overall. A high-quality weld is made using high-quality materials.
It should be remembered that welding over weld metal is actually a very common occurrence. Multi-pass welds after all are manufactured by welding over weld metal! There are also many accepted procedures in which welds overlap.