Rivet failure occurs when a rivet is no longer able to adequately perform its intended function of joining materials together due to exceeding its structural capacity or experiencing degradation. This can happen in several ways, all of which compromise the integrity of the connection.
Here's a breakdown of common rivet failure modes:
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Shear Failure: This is arguably the most common type of rivet failure. Shear failure happens when the forces acting on the connected plates are too great, causing the rivet to be "cut" or sheared across its cross-section. Think of it like trying to cut a bolt with a pair of scissors – the force applied eventually exceeds the bolt's shear strength, and it breaks.
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Bearing/Crushing Failure: Bearing failure (also known as crushing failure) occurs when the pressure between the rivet and the plate it connects becomes excessive. This high pressure can deform or crush either the rivet material or the plate material around the rivet hole, enlarging the hole and weakening the connection. As the reference text notes: If bearing stress on the rivet is too large so that contact surface between rivet and plate may get damaged, this is called crushing or bearing failure of rivet.
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Tension Failure (of the plate): While the rivet itself might remain intact, the force applied can exceed the tensile strength of the connected plates near the rivet hole. This can cause the plate to tear or fracture around the hole, leading to joint failure. This is typically classified as a failure of the joined material rather than the rivet itself, but it's important to consider in the context of rivet connection integrity.
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Edge Tearing: This occurs when a rivet is placed too close to the edge of a plate. Under load, the plate material between the rivet and the edge can tear away.
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Rivet Head Failure: The head of the rivet can fail due to excessive tensile or shear forces, causing it to pop off or deform significantly. This is less common than shear or bearing failure.
Factors Contributing to Rivet Failure:
- Incorrect rivet material: Selecting a rivet with insufficient strength for the application.
- Improper rivet installation: Over- or under-tightening can weaken the rivet.
- Corrosion: Environmental factors can degrade the rivet material over time.
- Fatigue: Repeated loading and unloading can lead to fatigue cracks and eventual failure.
- Excessive load: Applying loads beyond the design capacity of the riveted joint.
- Poor design: Incorrect rivet spacing or edge distance can weaken the joint.
In summary, rivet failure encompasses various mechanisms where the rivet's ability to maintain a secure connection is compromised, leading to joint instability or separation. Understanding these failure modes is critical for proper design, material selection, and installation to ensure the long-term reliability of riveted joints.
