Impact resistance of limpet shells: a study of local adaptations
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T.C. BIOLOGICAL AND BIOMIMETIC MATERIALS
Impact resistance of limpet shells: a study of local adaptations Niamh Harford1 · Nessa O’Connor1 · David Taylor2 Received: 4 May 2020 / Accepted: 21 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Limpets are molluscs which have a conical shell that is well adapted to resist fracture by impact from projectiles such as rocks during storms. We hypothesised that the impact strength of the shell varies depending where the animal is located, reflecting the relative risk of high-energy impact. We quantified shell impact strength for the species Patella vulgata using a normalised energy. Limpets located in exposed places on open rock surfaces were found to be more than twice as strong as those living constantly underwater (7.34 MJ/m4.6 v 3.48 MJ/m4.6). This difference was discussed using a theoretical model based on the physics of projectiles moving through fluids. Limpets located in rocky crevices had an intermediate impact strength (5.43 MJ/m4.6), attributed to the reduced probability of impact in these locations. Differences in impact strength were found to be linked to two geometric parameters: apex thickness and the ratio of apex height to rim diameter. Combining the present results with data from previous work, we developed a theoretical model which was able to predict impact strength accurately as a function of rim diameter, apex height and apex thickness. These results demonstrate the considerable plasticity of form, which this species is capable of, helping to explain why it is so abundant. The findings may be valuable in the biomimetic development of lightweight impact resistant structures. Keywords Limpet · Habitat · Impact strength · Fracture · Shell
1 Introduction Molluscs such as the common limpet, Patella vulgata Linnaeus, 1758 protect themselves with a hard, rigid shell of calcium carbonate, which guards against predation, reduces water loss when the animal is exposed at low tide, and crucially provides mechanical resistance to physical impact. Impacts can occur during storms as a result of stones and other debris such as driftwood and ice which are thrown up by waves [1, 2]. For the limpet, the creation, growth and maintenance of the shell presumably involves considerable energetic cost. The problem is similar to that of designing an engineering structure to provide protection against impact which is also required to be relatively light in weight. Under these circumstances, information about the threat level—the * David Taylor [email protected] 1
Department of Zoology, Trinity College Dublin, Dublin, Ireland
Department of Mechanical & Manufacturing Engineering, Trinity Centre for Biomedical Engineering, Trinity College Dublin, Dublin 2, Ireland
2
size, velocity and probability of projectiles—is crucial in determining the optimal solution. The general ecology of limpets and related species has been extensively studied. Many, including Patella vulgata, are intertidal gastropods. They are known to be an important element
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