DAMAGE EVOLUTION IN COMPOSITE BONDED JOINTS UNDER FATIGUE LOADING
In the present paper the evolution of fatigue damage in composite bonded joints is extensively analysed and discussed, with particular reference to the influence of layer orientation at the adhesive-adherend interface, corner geometry at the end of the overlap area and stacking sequence. Single lap bonded joints manufactured from autoclave-moulded laminates were investigated under tension-tension fatigue loading. Two laminate lay-ups [45/02]s and [452/0]s , two overlap lengths (20 and 40 mm) and two corner geometry (square edge and fillet) were considered. The evolution of fatigue damage, a crack initiation followed by propagation up to a critical length, was investigated at macroscopic and microscopic level, by monitoring stiffness trends and by optical and scanning electron microscopy and it is extensively discussed in the paper. The presence of a 45° oriented layer at the adhesive-interface layer makes damage patterns and crack paths much more complicated with respect to 0° interface joints, previously investigated by the authors. As a result the resistance to crack propagation is increased.
Life prediction of bonded joints in composite materials
Abstract The paper presents a model for the prediction of the fatigue life of composite bonded joints. The model was developed on the basis of extensive experimental and numerical investigations, presented in the first [Quaresimin M, Ricotta M. Fatigue behaviour and damage evolution of single lap bonded joints in composite material. Compos Sci Technol, 2006;66:176–87] and second [Quaresimin M, Ricotta M. Stress intensity factors and strain energy release rates in single lap bonded joints in composite materials. Compos Sci Technol, 2006;66:647–56] part of this work. The model is based on the actual mechanics of the fatigue damage evolution and describes the joint lifetime as the sequence of a crack nucleation phase followed by a propagation phase. The nucleation phase was modelled by using a generalised stress intensity factor (SIF) approach, summarising the fatigue data to crack initiation in scatter bands in terms of generalised SIFs. The life spent in the propagation phase was obtained by integration of a Paris-like power law relating the strain energy release rate (SERR) to the rate of the crack growth. The Paris curves were obtained by combination of crack propagation data measured on the joints and functions describing the SERR variations with the crack length calculated via FE analysis. Several alternative combinations of crack propagation data and SERR components were compared to investigate their possible influence on the life prediction. The model validation provided a good agreement between predictions and experimental fatigue data obtained for single lap joints with different overlap length and corner geometry.
Balloon assisted translocation of the mitral anterior leaflet to prevent left ventricular outflow obstruction (BATMAN): A novel technique for patients undergoing transcatheter mitral valve replacement
Transcatheter mitral valve replacement (TMVR) is an option for patients at high risk for mitral valve replacement or repair via sternotomy or left thoracotomy approach. TMVR carries up to 22% risk of left ventricular outflow tract (LVOT) obstruction. Severe LVOT obstruction can have devastating hemodynamic and clinical consequences.