Mechanical behaviour of wood T-joints. Experimental and numerical investigation

Results of a double-shear single-dowel wood connection tested under monotonic quasi-static compression loading are presented and discussed in this paper. The wood used in this study was a pine wood, namely the Pinus pinaster species, which is one of the most important Portuguese species. Each connection (specimen) consists of three wood members: a centre member, loaded in compression along the parallel-tograin direction and two simply supported side members, loaded along the perpendicular-to-grain direction (Tconnection). The load transfer between wood members was assured by means of a steel dowel, which is representative of the most common joining technique applied for structural details in wooden structures. The complete load-slip behaviour of the joint is obtained until failure. In particular, the values of the stiffness, the ultimate loads and the ductility were evaluated. Additionally, this investigation proposed non-linear 3D finite element models to simulate the T-joint behaviour. The interaction between the dowel and the wood members was simulated using contact finite elements. A plasticity model, based on Hill’s criterion, was used to simulate the joint ductility and cohesive damage modelling was applied to simulate the brittle failure modes (splitting) observed in the side members of the joint. The simulation procedure allowed a satisfactory description of the non-linear behaviour of the T-joint including the collapse prediction

Determining mode I cohesive law of Pinus pinaster by coupling double cantilever beam test with digital image correlation

The direct identification of the cohesive law in pure mode I of Pinus pinaster is addressed. The approach couples the double cantilever beam (DCB) test with digital image correlation (DIC). Wooden beam specimens loaded in the radial-longitudinal (RL) fracture propagation system are used. The strain energy release rate in mode I (GI ) is uniquely determined from the load-displacement ( P ?? ) curve by means of the compliance-based beam method (CBBM). This method relies on the concept of equivalent elastic crack length ( eq a ) and therefore does not require the monitoring of crack propagation during test. The crack tip opening displacement in mode I ? ? I w is determined from the displacement field at the initial crack tip. The cohesive law in mode I I I (? ? w ) is then identified by numerical differentiation of the I I G ? w relationship. Moreover, the proposed procedure is validated by finite element analyses including cohesive zone modelling. It is concluded that the proposed data reduction scheme is adequate for assessing the cohesive law in pure mode I of P. pinaster

7th Drug hypersensitivity meeting: part two

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Data reduction scheme for measuring GIIc of wood in end-notched flexure (ENF) tests

Numerical and experimental studies of end-notched flexure (ENF) fracture tests were performed to obtain mode II R curves for maritime pine (Pinus pinaster Ait.) wood in the radial-longitudinal (RL) crack propagation system. Three- (3D) and two-dimensional (2D) finite element analyses were conducted to determine the mode II release rate of the critical strain energy (GIIc). The 3D analysis revealed that a small spurious mode III component did not affect GIIc measurements and that the 2D model was very accurate. A new scheme for data reduction based on the equivalent crack concept is proposed to overcome the difficulties related to accurate crack length measurement during propagation. This method does not require previous experimental tests to obtain the elasticmodulus, which varies markedly for different wood specimens. Experimental ENF tests were performed to verify the numerical results. The results demonstrate the accuracy of the data reduction method proposed.FCT - POCI/EME/56567/200

Equivalent crack based mode II fracture characterization of wood

This paper reports a numerical study of the end notched flexure Pinus pinaster wood specimen. The main objective was to validate a data reduction method based on the equivalent crack concept, in order to avoid well-known difficulties in monitoring crack propagation. A cohesive linear softening damage model based on developed interface elements was used to simulate crack propagation. The equivalent crack proposed was related to the fracture process zone, whose effect on the perceived critical strain energy release rate was assessed. The equivalent crack was incorporated in a compliance-based beam method, which provided accurate values of the mode II critical strain energy release rate, G(IIc). Furthermore, compliance-based beam method does not require crack measurements during end notched flexure tests and additional tests to obtain elastic properties.FCT - POCTI/EME/45573/200

Mechanical behaviour of wood T-joints. Experimental and numerical investigation

Results of a double-shear single-dowel wood connection tested under monotonic quasi-static compression loading are presented and discussed in this paper. The wood used in this study was a pine wood, namely the Pinus pinaster species, which is one of the most important Portuguese species. Each connection (specimen) consists of three wood members: a centre member, loaded in compression along the parallel-tograin direction and two simply supported side members, loaded along the perpendicular-to-grain direction (Tconnection). The load transfer between wood members was assured by means of a steel dowel, which is representative of the most common joining technique applied for structural details in wooden structures. The complete load-slip behaviour of the joint is obtained until failure. In particular, the values of the stiffness, the ultimate loads and the ductility were evaluated. Additionally, this investigation proposed non-linear 3D finite element models to simulate the T-joint behaviour. The interaction between the dowel and the wood members was simulated using contact finite elements. A plasticity model, based on Hill’s criterion, was used to simulate the joint ductility and cohesive damage modelling was applied to simulate the brittle failure modes (splitting) observed in the side members of the joint. The simulation procedure allowed a satisfactory description of the non-linear behaviour of the T-joint including the collapse prediction

The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue

the primary objective of this work was to analyse the adequacy of the Double Cantilever Beam(DCB) test in determining fracture toughness under pure mode I loading of cortical bone tissue.A new data reduction scheme based on specimen compliance and the crack equivalent concept was used to overcome the difficulties inherent in crack monitoring during its growth. It provides a complete resistance curve, wich is fundamental in estimating the fracture energy. A cohesive zone model was used to simulate damage initiation and prpagation, thus assessing the efficacy of the proposed testing method and data reduction scheme. Subsequently, the DCB test was applied to evaluate the mode I fracture energy of hidrated and termally dehydrated cortical bone tissue from young bovine femur , in the tangential-longitudinal prpagation system. The results obtained demonstrate the efficaacy of the DCB test and the proposed data reduction scheme on the bone fracture characterization onder mode I loading