Themes: Fracture in Polymer-based Materials: Structure-Property Relationships

STRUCTURAL STUDY OF AP-HTPB COMPOSITE UNDER IMPACT LOADING

The impact response of a composite material is dependent on its microstructure. This study examines the effect of particle size and impact velocity on the temperature rise and strain rate in a composite material containing Ammonium Perchlorate (AP) crystals and Hydroxyl-terminated polybutadiene (HTPB) binder by combining computational and experimental work. Samples of AP-HTPB composite, with AP crystal sizes of 200 and 400 μm, respectively, are impacted at velocities ranging between 5-10 m/s. A volume fraction of 70-80% AP is maintained in each sample.
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INVESTIGATION OF THE CRACK DEFLECTION/PENETRATION PROBLEM IN EXTRUSION-BASED ADDITIVELY MANUFACTURED POLYMERIC MATERIALS

Components produced via polymeric additive manufacturing (AM), especially extrusion based methods, possess many weld lines between strands and layers. Thus, the failure of these structures is often dominated either by crack deflection between or crack penetration through individual strands. Two methods to predict the failure mode are those of Cook and Gordan, and of He and Hutchinson. In this work, the applicability of both approaches has been tested on four different polymeric materials. It was observed that the two criteria are quite limited in predicting the correct failure mode. Not only printing temperature also the formation of contact area, the diffusion between the individual strands as well as the resulting morphology of the material were found to play a key role for predicting the crack deflection/penetration problem.
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IN-SITU EXPERIMENTAL INVESTIGATION OF FATIGUE CRACK PROPAGATION MECHANISMS IN POLYMER ELECTROLYTE MEMBRANE OF FUEL CELL UNDER OVERLOADING EFFECT

The fatigue crack growth mechanisms in polymer electrolyte membranes of fuel cell are investigated under single overload conditions. In-situ SEM testing and in-situ optical microscopy testing combined with digital image correlation technique are conducted. The results show that the residual stress dominates the fatigue crack growth after the application of small overload cycle leading to subsequent fatigue crack growth retardation while larger overload cycle causes crack tip sharpening, resulting in fatigue crack growth retardation reduction or even acceleration.
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INFLUENCE OF TEMPERATURE AND TESTING MEDIA ON FATIGUE CRACK GROWTH PERFORMANCE OF POLYETHYLENE TESTED VIA CRACKED ROUND BAR SPECIMEN [Keynote]

Static loading test methods to characterize the resistance against slow crack growth use surfactants to shorten testing times. In comparison, the cracked round bar test method uses cyclic loading but no accelerating media and/or temperatures. To allow for a comprehensive knowledge on the effect of media influence, this research investigates the effect of air as well as deionized water with and without surfactant on the crack growth performance of blow-molding polyethylene in cracked round bar experiments at various temperatures. As also seen in literature, first test results show a crack growth decelerating effect of surfactant in cyclic tests at an elevated temperature. Ongoing tests will show the temperature dependency of these effects.
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REACTIVE TELECHELIC POLYETHERIMIDE TOUGHENED TETRAFUNCTIONAL EPOXY

Highly crosslinked multifunctional epoxy resins possess superior properties, like high Tg, modulus, chemical resistance, etc, yet they are brittle due to their high crosslink density. It is desired that toughness improvements should not compromise other properties, including mechanical, thermal properties, and processability. Here, reactive polyetherimide containing amine functional end groups with two different molecular weights and loading levels were incorporated in tetraglycidyl diamino diphenyl methane tetrafunctional epoxy resin to study their structure-property relationship.
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FRACTURE CHARACTERIZATION OF DUCTILE POLYMERS: RECENT APPLICATIONS OF THE LOAD SEPARATION CRITERION

For ductile polymers, the development of sound relationships between material structure and fracture response calls for the use of robust testing methodologies able to measure properties that describe the different processes occurring during fracture. The most common testing methods used with these materials appear inadequate, and there is a need to examine new approaches. This paper describes the most recent applications of the load separation criterion (LSC) in the fracture characterization of ductile polymers: the testing procedures are introduced and some representative results shown.
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RUPTURE OF HYDROGELS

Hydrogels are soft, highly deformable materials with applications ranging from soft actuators to natural and synthetic biomaterials. The rupture of hydrogels generally involves very large deformations that can be strongly coupled to the fluid flow. In this paper, a modified J-integral (J*) is used to calculate the critical energy release rate utilizing either a critical stretch criterion or the measured overall force-extension relation for a SENT specimen of a fibrin gel, which is the primary stress-carying component of blood clots.
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DUCTILE FAILURE OF A PLASTICIZED POLYVINYLCHLORIDE DURING AIR BAG DEPLOYMENT

The present work addresses the ductile fracture process of a plasticized Polyvinylchloride (PVC), constituting the skin of the dashboard, with the goal of ensuring the security of passengers for the automotive industry. Clamped single edge notch bending (SENB) specimens were used to characterize the mechanisms of crack initiation and propagation for the studied material. The ductile failure of the plasticized PVC, by using fracture mechanics tools, was characterized thanks to the exploitation of the experimental database associated with finite element simulation of the crack propagation.
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ENVIRONMENTAL STRESS CRACKING RESISTANCE (ESCR) OF RECYCLED PP (RPP) FROM AND FOR YOGURT CUPS

Recycling of plastic packaging waste is a promising approach towards a circular economy due to the high amount used and the short application time. This paper uses the concept of environmental stress cracking resistance (ESCR) to investigate the fatigue behavior of recycled yogurt cup materials. As test environments air and oil where chosen, where the latter imitates the fatty structure of yogurt. Therefore, four fractions of manually sorted post-consumer polypropylene yogurt cup waste was shredded to flakes and washed with different temperatures and media. Additionally, one of these fractions was blended with varying amounts of virgin pipe material. Furthermore, the reference material, which is currently used for yogurt cups was tested for comparison. Various influences of the fatigue tests were detected, which are a more pronounced influence of oil than of air, especially for recyclates but also for virgin materials and a significant improvement of the recyclates which were blended with a pipe grade material.
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