Fastening Materials
In P&O you will learn many methods of fastening materials together. Some of the most common methods include the use of rivets, screws, and glues:
- Screws and bolts
- Create clamp-up, friction, compressive forces
- Can support tension loads better than rivets and adhesives
- Rivets: aluminum, steel, cadmium-plated copper rivets, speedy
- Create compressive forces inside the radius of the hole
- More capable of supporting shear loads (loads perpendicular to the axis of the shaft)
- Welding, brazing, soldering
- Fusion of materials resists tension, compression and shear.
- Adhesives
- Distribute bond over a large area to reduce shear stresses
- Resist shear forces better than tension (opening) forces
- May be used to attach dissimilar materials
- Buckles, straps, string ties
- Fibers resist tension only in one direction relative to tensile strength of fibers
Material properties and characteristics relevant to the selection and application of fasteners in P&O.
- Type of loading that bonded joint will be subjected to – Type of load to be resisted, e.g., tension or shear
- Strength of bond: Temporary or permanent bond
- Type of surface to be joined, e.g., metal, plastic, foam
- Flexibility of bond: Brittle or ductile
- Ease of fabrication
- Appearance, color, odor, toxicity
Rules of thumb:
- Select fastener based on the type of load that needs to be resisted (tension or shear), surface, toughness, desire for permanence, ease of fabrication, toxicity (health), ease of use, and appearance.
- Screws and bolts create clamp-up, friction, compressive forces. They can support tension loads better than rivets and adhesives.
- Rivets create a compressive forces inside the radius of the hole
- Adhesives distribute bond over a large area. They resist shear forces better than tension forces.
- Fibers (straps) resist tension and only in the direction of the fibers.
- When fastening parts together, ALWAYS USE THE SAME type of fastener. NEVER combine rivets with bolts and screws in the same joint. In general, a joint composed of similar fasteners achieves a more consistent load distribution. However, this does not guarantee that all fasteners will reach their capacity simultaneously; therefore, fasteners need to be assessed during follow-up visits.
- Fabrication
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Holes in materials create stress concentrations
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The recommended minimum spacing between rivets is three times the nominal rivet diameter.
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The edge distance from the center of the hole to the end of the member should be at least twice the diameter of the rivet.
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- To achieve maximum tension, a screw should typically engage with at least 1.5 times the diameter of the screw in threads.
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Avoid failures with adhesives
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Surface prep: clean and rough up surface
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Select the right adhesive: consider environment and type of loading
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Properly apply the adhesive: not too thick, just right
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Performance Checklist
Fastening:
- PPE: Wear safety glasses, tie long hair back, no dangling clothing/jewelry.
- Name things: copper rivet, burr, speedy rivet, drill bit, drill bit gauge, countersink, ball peen hammer, diagnoal cutters
- Stabilize material and uses appropriate body mechanics when drilling.
- Copper rivet and burr are smooth on both sides, no sharp edges (that might scratch skin).
- Place the burr next to the non-metallic material and form new head to secure the burr.
- Do not need to use burrs when riveting metal to metal
- Always use burrs when riveting metal to leather, plastic or any non-metallic material
- Describe how to remove rivets without ruining original material.
- Countersink: knows when to use countersink tool.
- Describe how to select the appropriate size drill bit.
definition
The clamp-up force, also known as preload or clamp load, refers to the compressive force that clamps the joined components together.
When a screw or bolt is tightened, the rotational force applied (torque) is converted into axial tension, stretching the fastener slightly within its elastic limits. This tension creates a force pulling the fastener inwards, which in turn compresses the components it's holding together. This compressive force is the clamp-up force.