INFLUENCE OF LONG-TERM ANNEALING ON RESIDUAL STRESS DISTRIBUTION AND QUASI-BRITTLE FAILURE PROPERTIES OF TALCUM REINFORCED PIPE GRADE POLYPROYPLENE
In this study a polypropylene material with talcum reinforcement used for sewer pipes has been subjected to an annealing procedure at 80°C, roughly 60°C above the actual application temperature, in air for a time period of 18 months. As expected, examination of the material showed no significant decrease in mechanical or fracture mechanical properties due to the temperature exposure. However, samples stored at higher temperature showed better resistance against quasi-brittle failure in fatigue tests compared to unconditioned samples. This could mainly be attributed to the decrease of residual stress in the pipe wall. Even though pipes have been annealed for very long times above Tg, residual stress could not be totally relaxed within 18 months.
Characterisation of quasi-brittle fatigue crack growth in pipe grade polypropylene block copolymer
Abstract The aim of this work was to characterise quasi-brittle fatigue crack growth in a pipe grade polypropylene block copolymer. Cyclic cracked round bar specimen tests have been identified as a possible way to induce cyclic quasi-brittle crack growth within a reasonable amount of time. To ensure quasi-brittle failures, fracture surfaces have been examined using scanning electron microscopy. For further acceleration of the tests, higher temperatures with adapted load ranges have been applied. For 50 °C and 80 °C, a decrease in testing times of approx. 60% and 80% was achieved without significant changes in failure behaviour (e.g. cyclic crack opening displacement (Δδ) curves or fracture surfaces) of the tested specimens. Relationships between applied load and testing times, as well as between crack initiation and failure have been examined. A change in ratio of crack initiation to total failure time was observed at higher temperatures. This has to be considered in future tests, especially when comparing different types of polypropylene at temperatures, differing from the real application.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.