Hello and welcome to this new blog post. Today's topic is the creep performance of high performance polymers such as LCP, PEEK, PPS, and PPA. It is another important multipoint and long-term data set for polymer material selection and part design.
The creep strength and toughness of High Performance Plastics at different temperatures we discuss here.
Introduction to creep in plastics
Creep, also known as cold flow, is the deformation under a static load over time and helps to gain insights over the product lifetime. Understanding the creep behavior is one puzzle key during polymer material selection. Creep resistance materials are needed for applications such as structural components, joints, fittings and hydrostatic pressure vessels. In general we can distinguish between primary, secondary, and tertiary creep. When you conduct a creep test (for example according to ISO 899-1 or ASTM D2990) it is important to keep the applied stress on the material at a constant level. This allows in turn to plot the lifespan of your product.
Relevance of creep performance data for polymer material selection
As a polymer design engineer you are interested in creep data when you are dealing with application parts which are under high load for a long period of time. Overall, environmental changes impact the creep behavior too. Especially the increase of the temperature decreases creep performance dramatically. Also, for metal-to-plastic conversion, creep data are of essence.
Comparison long term creep performance of high performance polymers and die casting metals
Figure 1 presents the creep deformation data as a function of time for several ultra- and high performance polymers (PEEK, PAEK, PPS, LCP, PPA, PPA+PA66 blend, PARA, and PESU). Also, the creep performance of two die-casting metals (zinc alloy - ZAMAK3; aluminium alloy - AG3) is shown.
Comparing the results of the high performance polymers it can be shown that the initial elongation is higher compared to that of the aluminum alloy. However, the slope of the curve is in a similar range. Opposite is the case with the zinc alloy which displays severe creep after 100 hours at room temperature and a strength level of 100 MPa. In the case of zinc and also magnesium alloys, high performance polymers are able to outperform die-casting metals in a metal replacement scenario.
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| Figure 1: Creep data of high performance polymers vs. die casting metals (ISO 899-1). |
Conclusions
Considering creep data as long-term performance data during polymer material selection is a vital part during a metal-to-plastic conversion. It allows access to the handling of a static load at different temperatures and different times.
Thanks for reading and #findoutaboutplastics
Greetings
Herwig Juster
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Literature:
[1] https://www.findoutaboutplastics.com/2022/11/plastic-multipoint-design-data-creep.html
[2] Ketaspire PEEK Design Guide: https://www.syensqo.com/en/brands/ketaspire-peek/documents
[3] https://businessdocbox.com/Metals/95576253-Ems-grivory-material-technology-metal-replacement-with-engineering-polyamides-ron-hamilton-consultant-ems-grivory-uk.html
[4] https://www.sumitomo-chem.co.jp/sep/english/products/lcp/lcp_bs_kikai.html
[5] Ixef PARA Design Guide: https://www.syensqo.com/en/brands/ixef-para/documents
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