Biomechanics of wear in insect mouthparts
File(s)
Author(s)
Deegala Durage, Induja Dilanka Deegala
Type
Thesis or dissertation
Abstract
In this thesis, I investigate the determinants of wear in insect mouthparts, using a multi-scale approach that integrates nanomechanical testing and macroscopic wear assays. I begin by assessing whether Archard’s classic wear model is valid for the mandible cuticle. I quantify the wear resistance and material properties of the cuticle of three species: leafcutter ants, leafcutter bees, and hissing cockroaches, using nanowear and nanomechanical testing. Archard’s model failed to account for wear resistance at low loads and high hardness; I introduce an elasto-plastic form of Archard’s model, which addresses some of this discrepancy. However, neither of the models explains the hydration-modulated changes in wear resistance, nor the effects of other material deformation processes, but encapsulates those in Archard's wear coefficient $k$. To understand this discrepancy, I investigate whether fracture affects the outcomes of nanowear tests and how hydration-mediated changes modulate the wear resistance of the cuticle by conducting nano-scratch tests, dynamic mechanical analysis, and creep tests. I also incorporate callow leafcutter ant mandibles into these tests to investigate how cuticle maturation affects wear resistance. I find that fracture is unlikely to be significant at the small scales considered here, viscosity is the most likely origin of the modulation of wear resistance with hydration, and wear geometry is an essential consideration in interpreting the nanowear outcomes. Finally, I investigate the effect of substrate properties and mandible size on the wear by conducting wear assays on leafcutter ant mandibles. From controlled leaf-cutting experiments, I find that substrate’s toughness, critical stress, and modulus join mandible’s hardness and modulus as key factors that determine mandible wear in leafcutter ant-plant interactions. The outcomes of these studies improve understanding of the factors and mechanisms that determine the wear resistance of insect mouthparts and provide new insights into potential proxies for wear resistance in insect cuticles.
Version
Open Access
Date Issued
2025-11-14
Date Awarded
2026-07-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Labonte, David
Sponsor
UKERC (Organization)
Grant Number
851705
Publisher Department
Department of Bioengineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)