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Proper preparation of metallographic specimens to determine microstructure and content requires that a rigid step-by-step process be followed. In sequence, the steps include sectioning, mounting, course grinding, fine grinding, polishing, etching, and microscopic examination. Specimens must be kept clean and preparation procedure carefully followed in order to reveal accurate microstructures. Each student will prepare and examine a brass, steel or aluminium sample for metallographic examination. Additionally, a brass, steel or aluminum sample with different composition, a eutectoid steel sample and a eutectoid Pb-Sn sample will be examined under the metallographic microscope. Photographs will be taken of the samples and the ASTM grain size number determined for each of the specimens if applicable.

Quiz: Polymers and Fiber Reinforced Composite Materials

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Composites consist of two or more phases that are usually processed separately and then bonded, resulting in properties that are different from those of either of the component materials.

Polymer matrix composites generally combine high-strength, high-stiffness fibers (graphite, kevlar, etc.) with low-density matrix materials (epoxy, polyvinyl, etc.) to produce strong & stiff materials that are lightweight.

The mechanical properties of polymers vary significantly from polymer to polymer as a result of atomic structure and bond strength. Thermoplastic polymers are generally composed of long coiling carbon chains that are primary bonded along the chains, but are secondarily bonded between chains. Thermoplastics tend to either contain crosslinks (primary bonds between chains) or are composed of three-dimensional space networks, but thermosets tend to be comparatively expensive and can’t be recycled. The tensile properties of representative samples from the three primary polymer types (thermoplastics, thermosets and elastomers) will be tested and evaluated. When a polymer is subjected to a constant strain yet realizes a decrease in stress as a function of time, it is said to be undergoing Stress Relaxation. Two experiments will be conducted on polymeric samples to investigate their stress relaxation behavior. The quantifying parameter, Relaxation Time Constant, will be determined for the two samples tested.

Quiz: Fatigue Testing

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A perusal of the broken parts in almost any scrap yard will reveal that the majority of failures occur at stresses below the yield strength. This is a result of the phenomenon called fatigue which has been estimated to be responsible for up to 90% of the in-service part failures which occur in industry. If a bar of steel is repeatedly loaded and unloaded at say 85% of its’ yield strength, it will ultimately fail in fatigue if it is loaded through enough cycles.

Quiz: Heat Treatment - Quenching & Tempering

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Conventional heat treatment procedures for producing martensitic steels generally involve continuous and rapid cooling of an austenitized specimen in some type of quenching medium, such as water, oil, or air. The properties of a steel that has been quenched and then tempered depends largely on the rate of cooling and tempering times and temperatures. During the quenching heat treatment, the specimen can be converted to a variety of microstructures including soft and ductile spheroidite to hard and brittle martensite. The production of pearlitic and bainitic steels is lower in cost and suffices for most applications. Martensitic steels must be tempered prior to use due to their extreme brittleness. A range of heat treatments producing a variety of microstructures and mechanical properties will be investigated in this experiment beginning with a set of initially equivalent samples of SAE 1040 steel. Pearlite, Bainite and Martensite will all be produced through variations in the cooling rates of initially austenized samples.

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