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Shots of an anchor chain being tested to breaking point in a shipyard. Charles Newey introduces the programme. He discusses stretching as a method of testing the mechanical properties of materials.... Nick Reid briefly discusses two different methods of stretching materials in tests. Newey discusses the need for standard shapes of materials to be tested. He shows a dumbbell shape sheet metal specimen as an example. N.Reid with apparatus for testing the tensile strength of materials. He points out the components and explains how the apparatus works. The tensile strength of an aluminium alloy specimen is tested. Force/Extension curve is plotted on an oscilloscope screen up to the breaking point. Another aluminium specimen is tested in region I of the Force/Extension curve. As the force is is relaxed the extension returns to normal, demonstrating the elastic properties of the specimen in this region of the curve. Newey uses a model of the molecular structure of the specimen to explain the reason for the elasticity. The specimen is now stretched until its Force/Extension curve is in region 2. Force is then relaxed. This time a permanent deformation of the speciman results (plastic strain) . Newey explains the importance of determining the point of change from elastic to plastic for engineering materials. Micrograph of a specimen which has been stretched to its plastic region. Newsy uses a wooden model to show how the lines visible on the micrograph are caused. The aluminium alloy specimen is now stretched until its Force/Extension curve is in region 3. Curve is shown on oscilloscope screen. Close up shot of the specimen. A constriction has appeared and the specimen breaks at this point. Newey introduces sequence on tensile testing of polymers in this case polypropylene. He holds up a milk crate made of the material. Force/Extension curve for polypropylene specimen shown on the oscilloscope screen. Newey explains the phenomenon of viscoelasticity as seen in the curve above. He then uses a door mechanism as an analogue for the phenomenon. The polypropylene specimen is stretched further and its Force/Extension curve plotted. Cold drawing phenomenon is demonstrated. Another specimen of polypropylene is tested. The force is applied at a much faster rate and the specimen breaks. This demonstrates that plasticity as well as elasticity is time dependant. Newey explains why this is important when using polymers as engineering materials. Newey begins discussion of photo elasticity as a tool for determining stress on materials of particular shapes. Reid examines the distribution of stress in a dumbbell shaped stress piece. The specimen is stretched and stress contours can be seen under polarised light. Newey briefly discusses photoblastic tensile testing of notched materials. (Fracture toughness testing). Shot of a notched specimen under polarised light. Stress contours are seen.
Shots of an anchor chain being tested to breaking point in a shipyard. Charles Newey introduces the programme. He discusses stretching as a method of testing the mechanical properties of materials.... Nick Reid briefly discusses two different methods of stretching materials in tests. Newey discusses the need for standard shapes of materials to be tested. He shows a dumbbell shape sheet metal specimen as an example. N.Reid with apparatus for testing the tensile strength of materials. He points out the components and explains how the apparatus works. The tensile strength of an aluminium alloy specimen is tested. Force/Extension curve is plotted on an oscilloscope screen up to the breaking point. Another aluminium specimen is tested in region I of the Force/Extension curve. As the force is is relaxed the extension returns to normal, demonstrating the elastic properties of the specimen in this region of the curve. Newey uses a model of the molecular structure of the specimen to explain the reason for the elasticity. The specimen is now stretched until its Force/Extension curve is in region 2. Force is then relaxed. This time a permanent deformation of the speciman results (plastic strain) . Newey explains the importance of determining the point of change from elastic to plastic for engineering materials. Micrograph of a specimen which has been stretched to its plastic region. Newsy uses a wooden model to show how the lines visible on the micrograph are caused. The aluminium alloy specimen is now stretched until its Force/Extension curve is in region 3. Curve is shown on oscilloscope screen. Close up shot of the specimen. A constriction has appeared and the specimen breaks at this point. Newey introduces sequence on tensile testing of polymers in this case polypropylene. He holds up a milk crate made of the material. Force/Extension curve for polypropylene specimen shown on the oscilloscope screen. Newey explains the phenomenon of viscoelasticity as seen in the curve above. He then uses a door mechanism as an analogue for the phenomenon. The polypropylene specimen is stretched further and its Force/Extension curve plotted. Cold drawing phenomenon is demonstrated. Another specimen of polypropylene is tested. The force is applied at a much faster rate and the specimen breaks. This demonstrates that plasticity as well as elasticity is time dependant. Newey explains why this is important when using polymers as engineering materials. Newey begins discussion of photo elasticity as a tool for determining stress on materials of particular shapes. Reid examines the distribution of stress in a dumbbell shaped stress piece. The specimen is stretched and stress contours can be seen under polarised light. Newey briefly discusses photoblastic tensile testing of notched materials. (Fracture toughness testing). Shot of a notched specimen under polarised light. Stress contours are seen.
| Module code and title: | TS251, An introduction to materials |
|---|---|
| Item code: | TS251; 05; 1974 |
| First transmission date: | 26-03-1974 |
| Published: | 1973 |
| Rights Statement: | Rights owned or controlled by The Open University |
| Restrictions on use: | This material can be used in accordance with The Open University conditions of use. A link to the conditions can be found at the bottom of all OUDA web pages. |
| Duration: | 00:22:06 |
| Note: | Record previously confused with T251/03, VF1555, 'Thermal analysis'. |
| + Show more... | |
| Producer: | Colin Robinson |
| Contributors: | Charles Newey; Nick Reid |
| Publisher: | BBC Open University |
| Keyword(s): | Aluminium specimen; Force/extension curve; Fracture toughness; Instron machine; Laboratory testing; Photoelastic models; Polymer |
| Master spool number: | 6HT/71227 |
| Production number: | 00525_5065 |
| Videofinder number: | 1557 |
| Available to public: | no |
