Adhesives, Mechanical Restraint, and Material Properties
Adhesives and Mechanical Restraint
Mechanical Restraint
Mechanical restraint involves using different methods to hold materials together mechanically. These methods use separate hardware components, such as clips. Restraint methods are divided into two main classes:
- Those that create a permanent bond (e.g., rivets).
- Those that allow disassembly (e.g., threaded fasteners such as screws, bolts, and nuts).
Mechanical assemblies are preferred over other joining processes for several reasons:
- Manufacturing facility.
- Ease of assembly and transport.
- Ease of disassembly, maintenance, and parts replacement or repair.
- Easy to create designs that require mobile joints like hinges, sliding mechanisms, components, and adjustable brackets.
- Lower overall cost of manufacturing the product.
Adhesives
Adhesives involve applying bonding and sealing to integrate similar and dissimilar materials such as metals, plastics, ceramics, wood, paper, and cardboard. It is a joining process in which the filling material used to hold two (or more) parts together are very close by setting the surface. The filler material is the adhesive, a non-metallic substance, usually a polymer.
For adhesion mechanisms to operate successfully, the following conditions must prevail:
- The surfaces of the bonded parts should be clean and free of film, dirt, grease, and rust.
- The adhesive in its initial liquid form should completely wet the surface of the attached parts.
- It is usually helpful if the surfaces are not perfectly smooth; a slightly rough surface increases the real contact area and promotes mechanical interlocking.
Mechanical Properties of Materials
These are inherent characteristics that distinguish one material from another.
Stress-Strain Relationship
Static types of efforts that can affect materials include tension, compression, and shear. Tensile stresses tend to elongate the material, compression tends to compress it, and shear forces tend to slide adjacent portions of the material on one another.
Properties in Tension
This test applies a force tending to pull and elongate the material, reducing its diameter.
Compression Properties
In a compression test, a load crushes a cylindrical specimen, reducing its height and increasing its cross-sectional area.
Fold and Fragile Materials Testing
The angle is used to form sheets and sheet metal. The process of bending (or flexing) subjects the material to tensile stress (and deformation) in the outer half of the bent section, and compressive stress (and strain) on the inner half. If the material does not fracture, it will be permanently bent.
Properties for Shear
Shear involves applying effort in opposite directions on either side of a thin element to deflect it into a parallelogram.
Hardness
Hardness is the property of a material to resist scratching and cutting of its surface.
Industrial Scales
Hardness is measured with a durometer. The interest in determining the hardness of steels lies in the correlation between hardness and mechanical strength, making it a cheaper and faster test method than the tensile test.
The current industrial scales are:
- Brinell hardness
- Knoop Hardness
- Rockwell Hardness
- Rockwell superficial
- Hardness Rosiwal
- Shore Hardness
- Vickers hardness
- Webster Hardness
Viscosity is the property that determines the flow of fluids. Overall, viscosity can be defined as the characteristic resistance to flow of a fluid.
Viscoelastic Behavior of Polymers
Another property characteristic of polymers is viscoelasticity. This property determines the deformation of a material when subjected to combinations of stress and temperature over time. As its name implies, it is a combination of viscosity and elasticity.