Large strain cyclic fatigue testing of unidirectional carbon fibre reinforced epoxy resin

International audienceThe fatigue behaviour of a unidirectional carbon fibre reinforced epoxy resin subjected to large cyclic strains has been investigated. The development of a specific testing apparatus and procedure was found to be necessary so as to successfully test the unidirectional material in fatigue. A loop configuration has been used which allowed a gradual transfer of load from the testing machine to the specimen to be achieved without producing stress concentrations in the clamps. The results of the study reveal the existence of a fatigue mechanism for unidirectional carbon fibre reinforced epoxy resin which becomes evident under large cyclic strains, greater than 0.7%. This effect was seen to be a function of the loading level and whether the material was aged in humid conditions or not. Ageing lowered the threshold level for the onset of fatigue. The failure mechanisms involved have been revealed by scanning electron microscopy

Analysis of 51 cyclodipeptide synthases reveals the basis for substrate specificity.

International audienceCyclodipeptide synthases (CDPSs) constitute a family of peptide bond-forming enzymes that use aminoacyl-tRNAs for the synthesis of cyclodipeptides. Here, we describe the activity of 41 new CDPSs. We also show that CDPSs can be classified into two main phylogenetically distinct subfamilies characterized by specific functional subsequence signatures, named NYH and XYP. All 11 previously characterized CDPSs belong to the NYH subfamily, suggesting that further special features may be yet to be discovered in the other subfamily. CDPSs synthesize a large diversity of cyclodipeptides made up of 17 proteinogenic amino acids. The identification of several CDPSs having the same specificity led us to determine specificity sequence motifs that, in combination with the phylogenetic distribution of CDPSs, provide a first step toward being able to predict the cyclodipeptides synthesized by newly discovered CDPSs. The determination of the activity of ten more CDPSs with predicted functions constitutes a first experimental validation of this predictive approach