Wear 247 (2001) 100–108 Dependence of solid particle erosion on the cross-link density in an epoxy resin modified by hygrothermally decomposed polyurethane N.-M. Barkoula, J. Gremmels, J. Karger-Kocsis ∗ Institute for Composite Materials Ltd., University of Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern, Germany Received 27 March 2000; accepted 11 September 2000 Abstract Solid particle erosion of epoxy resin (EP) modified by various amounts of hygrothermally decomposed polyester-urethane (HD-PUR) was studied at oblique (30, 45, and 60 ◦ ) and normal impact (90 ◦ ). The cross-linked structure of the modified EP was characterised by the mean molecular weight between cross-links (M c ). It was established that the initial brittle erosion of the densely cross-linked EPs (M c ≤ 200 g/mol) changed to a rubbery one by increasing HD-PUR modification due to which a less cross-linked network was formed (M c > 1000 g/mol). This change was reflected by the impact angle dependence: compositions of low M c showed the minimum resistance at normal (90 ◦ ), whereas those of high M c at 30 ◦ impact angle. The resistance to solid particle erosion changed linearly with increasing fracture energy (G c ) of the resins. G c , on the other hand, followed the prediction of the rubber elasticity theory and increased linearly with M 1/2 c . © 2001 Elsevier Science B.V. All rights reserved. Keywords: Modified epoxy resin (EP); Solid particle erosion; Cross-link density; Fracture energy; Failure behaviour 1. Introduction Polymers and related composites are widely used as engineering parts in various application fields where high resistance to wear, abrasion and erosion is required (mining, energetics, transportation, etc.) [1]. As a consequence, the erosion wear performance of polymeric systems became under spot of interest recently. Albeit polymers and related composites possess outstanding mechanical and thermal properties, many of them show rather poor resistance when exposed to fast moving erodents [2]. The latter occurs very frequently in the praxis. The erosion behaviour of polymeric materials depends first of all on their nature. Thermosetting polymers, such as epoxy (EP) and phenolic resins, show brittle erosion whereas the erosion response of thermoplas- tics is of ductile type [3]. The same categorisation applies for the related composites. It was demonstrated that the maximum erosion rate is at an oblique impact angle of 30 ◦ and at 60–90 ◦ for ductilety and brittely eroding polymers, respectively [1,3–7]. Rubbers, on the other hand, present a ∗ Corresponding author. E-mail address: karger@ivw.uni-kl.de (J. Karger-Kocsis). maximum erosion rate at 30 ◦ , but the failure mechanisms differ from those of thermoplastic resins. It is, therefore, a great challenge to study the solid particle erosion of a system that may show both brittle and ductile erosion behaviour depending on its composition and struc- tural characteristics. According to the authors knowledge this has not been done so far. Recently, it was reported that the mechanical property profile of tri-and tetrafunctional EP resins can be varied in a very broad range by mod- ifying them with hygrothermally decomposed polyester- urethane (HD-PUR) [8,9]. HD-PUR works as an active diluent (being an amine containing compound) and phase separation modifier at the same time in EP resins. The prop- erties of the EP/HD-PUR systems can be set between those of cross-linked thermosets and rubbers via the HD-PUR amount. Modification of EP by HD-PUR results in a chem- ical network of lower cross-link density. This fact allows us to investigate the erosive behaviour as a function of network characteristics. The aim of this study was to in- vestigate the effects of external testing conditions (impact angle) and internal material parameters (cross-link density) on the erosion behaviour of HD-PUR modified EP resins. A further aim of this study was to find a correlation between 0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0043-1648(00)00529-9