Mechanical fatigue fractures bivalve shells

Mollusk shells defend against a lifetime of environmental and predatory threats. The dangers range from single, high-magnitude impacts, to chronic, low-magnitude stresses. Using the California mussel, Mytilus californianus, as a model system, we investigated shell's ability to resist a ranges of forces using three different mechanical tests: a traditional test of shell strength, in which a valve was compressed between two flat plates until fracture, and two tests of fatigue resistance. Specifically, we tested cyclic fatigue resistance by loading valves repeatedly to a predetermined force until fracture, and static fatigue resistance by loading valves at a constant force until fracture. The results of these experiments are documented in CraneDenny_2020_SummaryMechanicalData.csv, which reports the results of the mechanical test of each valve; CraneDenny_2020_PairedMechanicalData.csv, which reports the same data as the Summary Mechanical Data, but is organized by mussel shell; and CraneDenny_2020_CycleMechanicalData.csv, which reports summary data for every cycle of loading in strength and cyclic fatigue experiments. Further details of the contents and organization of each spreadsheet are reported in the respective README files. Additionally, we tested the forces that mussels are able to generate themselves. We measured the magnitude of the constant opening force generated by the mussel hinge (reported in CraneDenny_2020_HingeStrength.csv), and we measured the force required to pry open a closed mussel (reported in CraneDenny_2020_MuscleStrength.csv). Further details of the contents and organization of each csv are reported in the respective README files.