Question

Generally, in welded joints, the maximum size of fillet weld is considered by

• A. adding \(1.5 \text{ mm}\) to thickness of thinner member to be jointed
• B. adding \(3 \text{ mm}\) to thickness of thinner member to be jointed
• C. subtracting \(3 \text{ mm}\) from thickness of thinner member to be jointed
• D. subtracting \(1.5 \text{ mm}\) from thickness of thinner member to be jointed

Hint:

Fillet weld sizing guide parameters: - For square plate edges: \(s_{\max} = t_{\text{thinner}} - 1.5 \text{ mm}\) - For round/rolled sections: \(s_{\max} = \frac{3}{4} \cdot t_{\text{section}}\) This structural margin keeps the edge from melting completely, preserving the base metal geometry.

Answer 1

The Correct Option is D

Concept: In structural welding design, a fillet weld joins two surfaces at approximately right angles. The size of a fillet weld (\(s\)) refers to the leg length of the largest inscribed isosceles right triangle forming the weld cross section. To ensure structural integrity and prevent stress concentration or burning of the base metal, engineering design standards (such as IS 800 and AWS specifications) define strict limits for weld sizing based on the plate thickness (\(t\)):
• Minimum Size of Fillet Weld (\(s_{\min}\)): Avoids rapid cooling rates that can cause brittleness in thick sections. It depends on the thickness of the thicker plate component being joined.
• Maximum Size of Fillet Weld (\(s_{\max}\)): Prevents the weld pool from spilling over the outer edges and ensures the corner remains un-melted, maintaining structural definition. It depends on the thickness of the thinner plate member (\(t\)). Let us look at the standard rules for specifying the maximum weld size across different plate boundary profiles:

Step 1: Examining the design rule for square edges.
When a fillet weld is applied along the straight square edge of a structural plate member, the maximum size of the leg length must be limited so that the arc heat does not burn away the outer corner. The standard design rule specifies: \[ s_{\max} = t - 1.5 \text{ mm} \] Where \(t\) is the thickness of the thinner member being jointed. This matches the wording of Option (4).

Step 2: Examining the design rule for rounded/rolled edges.
For plate components with rounded boundaries, such as the toe of a structural rolled steel channel or angle section, the maximum size is bounded by the profile curvature: \[ s_{\max} = \frac{3}{4} \times t \]

Step 3: Confirming the choice.
Since the prompt refers generally to plate thicknesses without specifying a rounded profile, the standard square-edge design boundary applies. Therefore, the maximum size of the fillet weld equals the thickness of the thinner member minus \(1.5 \text{ mm}\). This aligns with Option (4).