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A two-body abrasive wear model as a contact-induced fracture process
A recent work by the researchers from Leibniz University Hannover presents a 3-D framework for simulation of contact-driven-fracture processes (like abrasive wear) in filled elastomers. Modeling of material removal processes, like wear, to this day remains an empirical art. Since the prolific work of J. F. Archard in the 1950s, several non-transferable ad hoc wear models, purely based on macroscopic parameters like sliding velocity/pressure, etc, have been proposed (based on Archard’s law) claiming to model the process of wear. Thus, suggesting a lack of understanding of the essential physics involving the process of wear, particularly in elastomers.
Abrasive wear, in elastomers is hypothesized as a two-step process. The first step occurs at the micron scale due to the contact between the sliding body and the asperities of the rough surface resulting in tensile stresses and crack initiation. Contact stresses (during the stick phase of contact) resulting from the sharp asperities and adhesion act as a primary driving force for quasi-static growth of the initiated cracks and finally resulting in detachment of particles 1 – 5 micrometers The second step, not addressed in this work, can be considered to occur at the macroscale where the detached particles act as an initiated macro-crack and growing due to a fatigue process. Such crack propagations can be hypothesized as leading to separation of larger pieces of few hundred microns in size.
In this work, the first step of the process is considered for modeling. Firstly, a micromechanical model is developed to describe the geometric and mechanical behavior of the polymer at the micro- and mesoscale. Particle-reinforced polymers at these length scales can be considered as a three-phase material consisting of free elastomer whose properties are equivalent to the unfilled system, bound rubber or an interfacial rubber between the filler and unfilled polymer and filler clusters.
Further on, a 3-D quasi-static fracture framework is implemented for large deformation fracture in polymers. Starting with simple, cohesive zone approaches, the framework is stabilized for usage at large deformations. The developed method is validated through comparison with experimental results. The last numerical method explored in this work is contact formulation for contact over rough surfaces, and this is in the form of a segment-to-segment Mortar method and as a contact element. The developed contact approach is validated using simple examples like hertz problem etc.
Combining all the above-developed methods, contact-induced fracture process on the microstructure is modeled considering RVE’s of different PHR levels. Overall, this works brings to light the elastic contributions towards abrasive wear and additionally builds a first representative idea towards a comprehensive physics-based understanding of multiscale processes like fracture and wear across the percolation threshold.
Further details: Ajay B.Harish, Peter Wriggers, Modeling of two-body abrasive wear of filled elastomers as a contact-induced fracture process, https://doi.org/10.1016/j.triboint.2019.05.009