Question

questions

1. what practical significance does the deflection temperature test have in making material selections for plastics products? give at least one example of an application where knowing the hdt might be important, e.g., \knowing hdt is important for roof trusses\.
2. is the hdt a thermal transition temperature? why or why not?
3. if the specimen is mounted on two supports, why is this type of loading called three - point bending?
4. does the deflection temperature test performed in this experiment meet astm d648 requirements? if not, what would disqualify this as an astm test?
5. what are the test hdt and published hdt values for your materials?
6. find and identify the source of published hdt values for comparison. do the test hdt values correlate with published data? if so, how well do they correlate? if they do not agree, discuss what you believe caused the discrepancy. (correlation and agreement responses should be numerical, e.g., \test hdt values agree with published hdt values by at least 87% for all tested materials\).
7. which of the tested plastic materials would be the best choice for a container that must support its contents while in a steam bath? why?

Explanation:

1. The Deflection Temperature test (HDT - Heat Deflection Temperature) helps in material selection as it indicates the temperature at which a plastic begins to deform under a specified load. For example, in the production of plastic pipes for hot - water systems, knowing the HDT ensures the pipes can withstand the operating temperature without deforming.
2. HDT is a thermal transition temperature as it marks the point where a plastic changes from a relatively rigid state to a more flexible one under load due to heat.
3. In three - point bending, the specimen is mounted on two supports and a load is applied at a point between the two supports, creating three points of interaction (the two supports and the loading point).
4. To determine if the Deflection Temperature test meets ASTM D648 requirements, one must check if the test conditions (temperature increase rate, load applied, specimen dimensions etc.) match those specified in the standard. Deviations in these factors could disqualify it as an ASTM test.
5. The test HDT values are obtained from the actual experiment on the materials, while published HDT values are from reliable sources such as material data sheets or scientific literature.
6. Sources of published HDT values can include material manufacturers' data sheets, scientific journals, or industry standards documents. Comparing test and published values helps assess the accuracy of the experiment. Discrepancies could be due to differences in test conditions, material batch variations etc.
7. The plastic material with the highest HDT among the tested ones would be the best choice for a container in a steam bath as it can withstand the high temperature without deforming and support its contents.

Answer:

1. It helps in ensuring the plastic can withstand operational temperatures without deforming. Example: plastic pipes for hot - water systems.
2. Yes, as it marks the transition from rigid to more flexible state under load due to heat.
3. Because there are two supports and a loading point between them.
4. Check test conditions against ASTM D648. Deviations in temperature rate, load, specimen size etc. could disqualify.
5. Test HDT from experiment, published from data sheets or literature.
6. Sources: manufacturers' data sheets, journals etc. Compare to assess accuracy. Discrepancies from test conditions, material variations.
7. The material with the highest HDT as it can withstand high temperature without deforming.