Question

The failure modes that may be observed in a riveted joint to fasten two plate members, subjected to shear load are

• A. bending of the rivet
• B. shearing of the rivet
• C. tensile failure of a plate member
• D. tensile failure of the rivet

Hint:

For a standard riveted or bolted joint loaded in shear, think about what can break:
1. The rivet can get {sheared} off.
2. The plate can get {torn} apart (tensile failure).
3. The rivet/plate interface can get {crushed} (bearing failure).
Bending is also a possibility, especially in lap joints.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
This question asks for the possible ways a riveted lap or butt joint can fail when it is loaded in shear (i.e., when the plates are pulled in opposite directions along their plane).
Step 2: Detailed Analysis of Failure Modes:
Consider a simple lap joint with one or more rivets, where the plates are pulled apart.
- (B) shearing of the rivet: The primary load on the rivet is shear. The plates pull on the rivet in opposite directions across the shear plane. If the shear stress exceeds the shear strength of the rivet material, the rivet will be cut in half. This is a primary and common failure mode. Therefore, (B) is a correct failure mode.
- (C) tensile failure of a plate member: The load is transferred through the plate. At the cross-section where the rivet holes are located, the area of the plate is reduced. The tensile stress in this "net section" is higher than in the gross section. If this stress exceeds the tensile strength of the plate material, the plate itself can tear apart. This is also known as tearing of the plate. This is a primary and common failure mode. Therefore, (C) is a correct failure mode.
- (A) bending of the rivet: In a lap joint, the line of action of the forces in the two plates is offset. This eccentricity creates a bending moment on the joint, which in turn causes the rivet to bend. While joints are designed to minimize this, rivet bending is a real deformation mode and can contribute to joint failure, especially in long rivets or single-lap joints. Therefore, (A) is a possible failure mode.
- Other common modes not listed as main options:
- Bearing/Crushing Failure: The rivet can crush the plate material it is bearing against, or vice-versa, elongating the hole.
- Shear-out/Tearing of the plate margin: The plate can tear out from the rivet hole to the edge of the plate.
- (D) tensile failure of the rivet: The primary load on the rivet in a shear-type connection is shear, not tension. Tensile failure would involve pulling the rivet head off, which is the primary failure mode in a tension-type connection, not a shear-loaded one. Therefore, (D) is not a typical failure mode for a shear-loaded joint.
Step 3: Why This is Correct:
The standard design calculations for riveted joints always check for shear failure of the rivet, tensile failure of the plate at the net section, and bearing failure. Bending of the rivet is also a recognized mechanism, particularly in lap joints. Therefore, (A), (B), and (C) represent valid failure modes. Tensile failure of the rivet itself is not characteristic of a shear connection.