(A) Tensile Testing of Engineering Materials
Different types of materials have different microstructures (structure at the sub-milimetre level), which directly control their different mechanical properties. The exploration and mapping of those properties allows the right materials to be selected and used in the right application.
Three broad categories of materials are commonly used in engineering: metals, ceramics and polymers, as well as combination of those (composite materials). This experiment aims to study mechanical properties of three materials and also to demonstrate the factors that affect the mechanical strength of the materials.
Tensile testing is the application of a force to a material until it fails (stretching a material until it breaks). Tensile stress is the instantaneous load applied to a specimen divided by its cross sectional area before any deformation, and the formula is σ = F / Ao . Young's Modulus (E) is the ratio of stress to strain when deformation is totally elastic (initial linear region), with the formula as E = σ / ε or stress / strain.
The figure to the left is a typical stress-strain curve.
*Ultimate Tensile Strength: maximum stress before fracture
* Ductility: measure of a material's ability to undergo appreciable plastic deformation before fracture
* Toughness: measure of the amount of energy absorbed by a material as it fractures
* Elastic vs. Plastic region: an item stretched in the elastic region can return to original state, but an item stretched in the plastic region will be deformed
1. To understand different mechanical properties of materials
2. To observe how the three types of materials behave in heir mechanical properties under the tensile and bend test
3. To understand the major factors which determine those mechanical properties
(B) Scanning Electron Microscope (SEM)
Electron Microscopes were developed due to limitations of Light Microscopes which are restricted by the physics of light to 500x or 1000x magnification and a resolution of 0.2 micrometers where human hair is around 0.1 micrometers.
The first Scanning Electron Microscope (SEM) debuted in 1942, uses a beam of highly energetic electrons to examine objects on a very fine scale. The sample examined is swept by the electron beam across its surface. The signals generated by interaction of the electron beam with the sample are collected by a variety of detectors, which provide us the topography (the surface feature and its texture), morphology (the shape and size of the particles making up the object) and composition (the chemical elements and compounds).
We used a virtual SEM that simulates the real SEM for safety fears and space limitations.
1. Basics of Scanning Electron Microscopy theory and instrumentation
2. Basics of Signal Detection theory and instrumentation for Secondary Electrons (SE), Backscattered Electrons (BSE) and Energy Dispersive X-ray (EDX) detectors
(C) Composite Material Processing
A composite material is a combination between two or more materials. It has the desirable properties which cannot be obtained by either of the constituent materials acting alone.
Composite materials are used because they are cheaper, lighter, stronger, has favourable properties (as determined by the manufacturer) and relatively easy to shape (during the processing stage). Some applications of composites include airplanes and sports equipments.
There are three types of composites: Dispersion Strengthened Composites (Examples are aluminum oxide, silicon carbide reinforced aluminum, which are used in high-performance bicycle frames), Particle-reinforced Composites (Examples are plastic which contain filler materials, and carbide cutting tools) and Fiber-reinforced Composites (Examples are fiberglass and carbon-fiber composites, used in high-performance air craft and sports equipment). We will be dealing with fiber-reinforced composites in this experiment.
1. To understand what is composite materials and how to fabricate them
2. To appreciate the applications of composite materials in daily life
3. To appreciate the mechanical properties of composites