Ductile adhesively-bonded timber joints - Part 1: Experimental investigation

In the field of timber load-bearing structures, adhesive bonding is a promising joining technique that may increase the structural stiffness and capacity of timber joints and structures. The use of ductile adhesives may furthermore allow designing ductile joints, which can compensate for the material ductility that timber lacks. To demonstrate the potential of this approach, adhesively-bonded double-lap timber joints were manufactured using a ductile acrylic adhesive and then subjected to axial tension and compression loading. The load-displacement responses were measured and compared to those of the same joint configuration for which a brittle epoxy adhesive was used. The effect of the different adhesives on the joint capacity and ductility has been studied and quantified. Strain field measurements using the Digital Image Correlation (DIC) technique and a quadratic strain interaction criterion provided a better understanding of the mechanical behavior of the two different joint types

Comparison of genetic programming with conventional methods for fatigue life modeling of FRP composite materials

Genetic programming is used in this paper for modeling the fatigue life of several fiber-reinforced composite material systems. It is shown that if the genetic programming tool is adequately trained, it can produce theoretical predictions that compare favorably with corresponding predictions by other, conventional methods for the interpretation of fatigue data. For the comparison of results, curves produced by the genetic programming tool are plotted together with curves produced by three other commonly used methods for the analysis of composite material fatigue data: linear regression, Whitney&psila;s Weibull statistics and Sendeckyj&psila;s wear-out model. The modeling accuracy of this computational technique, whose application for this purpose is novel, is very high. The proposed modeling technique presents certain advantages compared to conventional methods. The new technique is a stochastic process that leads straight to a multi-slope S-N curve that follows the trend of the experimental data, without the need for any assumptions. [All rights reserved Elsevier]

Stiffness degradation and life prediction of adhesively- bonded joints for fiber-reinforced polymer composites

Adhesively-bonded joints, including double- and stepped- lap joints (DLJs and SLJs), were experimentally investigated under cyclic tensile loading. The joints were composed of pultruded GFRP laminates and epoxy adhesive. A critical stiffness was found for DLJs and a critical elongation for SLJs at which failure occurs independently of load level. Based on measured uniform stiffness degradation during the fatigue life of DLJs, a linear model of stiffness degradation was established. For SLJs, after crack initiation, stiffness decreased at a higher rate during the initial and final stages of crack propagation. A non-linear sigmoid model was established. Results of both models compared well to experimental results and enabled F-N curves suitable for design to be established. © 2008 Elsevier Ltd. All rights reserved