tailieunhanh - Dynamic Mechanical Analysis part 4

Tham khảo tài liệu 'dynamic mechanical analysis part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | strain bold a FIGURE Examples of types of creep tests a Multiple creep-recovery cycles b multiple creep cycles with overlaying temperature ramp and c heat-set cycle. Time in minutes Stress Pa dashed b 1999 CRC Press LLC FIGURE Continued . Time t c 1999 CRC Press LLC placing the part into a specific environment such as a gasket in a pump down an oil well or a plastic pipe in an Alaskan winter. This environmental testing is not limited to temperature as creep-recovery tests can also be run in solvents or in controlled atmospheres. You can also vary the temperature within one creep cycle as shown in Figure . This is the equivalent of the rubber industry s heat-set test used for materials that will be heated and squeezed at the same time. The creep stress is applied and the material is heated to a set temperature and cooled back to room temperature while still under the load. The stress is removed and the amount of recovery recorded. A final comment on creep testing is that the American Society for Testing and Materials ASTM 12 does have standard procedures for creep tests that supply guidelines for both testing and data interpretation. The main method for plastics is D 2990-91. It covers tensile compressive and flexural creep and creep rupture. A QUICK LOOK AT STRESS RELAXATION EXPERIMENTS The conceptual inverse of a creep experiment is a stress relaxation experiment Figure . A sample is very quickly distorted to a set length and the decay of the stress exerted by the sample is measured. These are often difficult experiments to run because the sample may need to be strained very quickly. They do provide some very useful information that complements creep data. Creep data and stress relaxation data can be treated as mainly reciprocal 13 and roughly related as e e ơo ơt . i t o creep o t stress relax The analysis of the stress relaxation curve is shown in Figure and is analogous to the creep analysis. One interesting application of the .