TY - THES

T1 - Investigating novel concepts to characterize the resistance against rapid crack propagation of polyamide 12 pipe grades

AU - Waly, Christoph

N1 - embargoed until 26-02-2022

PY - 2021

Y1 - 2021

N2 - In the present work, polyamide 12 (PA12) pipe grades, which differ in their molecular structure (neat PA12 or compounded) and use of additives (i.e. impact modification and/or pigmentation), were tested by three new accelerated test methods, aiming to characterise the resistance against Rapid Crack Propagation (RCP). These include a modified form of a Charpy impact test (so-called "Modified Charpy"), a novel test apparatus designed to imitate the stress conditions in a pipe under internal pressure, called the "Notched Hoop-stressed Impact (NHI)” test and finally the presentation of a fracture mechanics test method, termed "Quasi-dynamic KID,eq". While the modified Charpy test is based on an already existing test concept, the NHI test as well as the quasi-dynamic KID,eq test represent completely new approaches for the characterization of RCP. In order to quantify a reliable material ranking with regard to RCP resistances, all PA12 grades were tested via standardized Small-Scale Steady-State (S4) test according ISO 13477. Results of newly developed approaches were then compared to S4 results in order to check for their reliability and quantitative significance with regard to RCP resistances. Using the modified Charpy test, the materials showed a different ranking related to the critical pressure values pc-S4 from the S4 test and therefore could not be classified correctly. If the critical temperature values Tc-S4 are considered, a ranking of the pipe grades results which agrees positively with the S4 test. However, the Underlying idea of reaching a Plateau of unchanging ideal brittleness was not achieved due to measurement restrictions. With the NHI test it was possible to evoke different stress states and the associated failure modes in the test specimens, ranging from brittle to ductile. The results of the NHI test also did not provide agreement with respect to pc-S4 from S4 ranking. A ranking in terms of Tc-S4 in contrast seems possible. The quasi-dynamic KID,eq test shows high potential for similar ranking of the materials with regard to their RCP resistance as provided by the S4 test, by using low temperatures, appropriate loading speeds and the Advantages of dominating plane strain conditions of Cracked Round Bar (CRB) test specimens. Using this method, it seems possible to rank the investigated materials by pc-S4. It was demonstrated that all methods were able to rank the PA12 types as long as the classification refers to pc-S4 or Tc-S4. Furthermore, a significant advantage of the accelerated methods in terms of shortened testing times, reduced testing effort and lower costs compared to the S4 test can be attested.

AB - In the present work, polyamide 12 (PA12) pipe grades, which differ in their molecular structure (neat PA12 or compounded) and use of additives (i.e. impact modification and/or pigmentation), were tested by three new accelerated test methods, aiming to characterise the resistance against Rapid Crack Propagation (RCP). These include a modified form of a Charpy impact test (so-called "Modified Charpy"), a novel test apparatus designed to imitate the stress conditions in a pipe under internal pressure, called the "Notched Hoop-stressed Impact (NHI)” test and finally the presentation of a fracture mechanics test method, termed "Quasi-dynamic KID,eq". While the modified Charpy test is based on an already existing test concept, the NHI test as well as the quasi-dynamic KID,eq test represent completely new approaches for the characterization of RCP. In order to quantify a reliable material ranking with regard to RCP resistances, all PA12 grades were tested via standardized Small-Scale Steady-State (S4) test according ISO 13477. Results of newly developed approaches were then compared to S4 results in order to check for their reliability and quantitative significance with regard to RCP resistances. Using the modified Charpy test, the materials showed a different ranking related to the critical pressure values pc-S4 from the S4 test and therefore could not be classified correctly. If the critical temperature values Tc-S4 are considered, a ranking of the pipe grades results which agrees positively with the S4 test. However, the Underlying idea of reaching a Plateau of unchanging ideal brittleness was not achieved due to measurement restrictions. With the NHI test it was possible to evoke different stress states and the associated failure modes in the test specimens, ranging from brittle to ductile. The results of the NHI test also did not provide agreement with respect to pc-S4 from S4 ranking. A ranking in terms of Tc-S4 in contrast seems possible. The quasi-dynamic KID,eq test shows high potential for similar ranking of the materials with regard to their RCP resistance as provided by the S4 test, by using low temperatures, appropriate loading speeds and the Advantages of dominating plane strain conditions of Cracked Round Bar (CRB) test specimens. Using this method, it seems possible to rank the investigated materials by pc-S4. It was demonstrated that all methods were able to rank the PA12 types as long as the classification refers to pc-S4 or Tc-S4. Furthermore, a significant advantage of the accelerated methods in terms of shortened testing times, reduced testing effort and lower costs compared to the S4 test can be attested.

KW - Rapid Crack Propagation (RCP)

KW - Polyamid 12

KW - Rohrtypen

KW - Rapid Crack Propagation (RCP)

KW - Polyamide 12

KW - Pipe grades

M3 - Master's Thesis

ER -