Meeting Abstract

P1.90  Thursday, Jan. 3  The eternal tug: fatigue failure of wave-swept macroalgae in conditions of repeated subcritical loading. MACH, K.J.; Hopkins Marine Station of Stanford University mach@stanford.edu

A seaweed on a wave-swept shore may endure more than 8000 wave-induced loadings each day. Perhaps not surprisingly, many intertidal seaweeds experience dislodgment and breakage in particular seasons as well as throughout the year. Typical assessments of algal material properties, such as breaking strength, involve pull-to-break tests applying a single, increasing load until breakage occurs. These traditional pull-to-break biomechanical tests have often predicted no, or very little, breakage in algal populations upon comparison of measured strength and maximum wave-imposed drag forces. I employ an alternate strategy to assess algal breakage, considering failure in the context of repeated wave-induced loadings. I use a standard method of fatigue analysis, applying repeated loading cycles comparable to field conditions, to characterize fatigue behavior in the red macroalgae Mazzaella. In this way, I generate plots of loading stress versus number of cycles to failure. Using Miner�s rule to sum accumulated fatigue damage, I predict failure in various field wave conditions from these laboratory-generated baseline fatigue data. Such examination of fatigue in seaweeds promises to clarify the discrepancy between known and traditionally predicted algal breakage rates.