jmc-xavier

Abstract Probabilistic fatigue models are required to account conveniently for several sources of uncertainty arising in the prediction procedures for structural details, such as the scatter in material behaviour. In this paper, a procedure to derive probabilistic S-N fields for structural details [1] is applied to a notched geometry with elliptic central hole made of puddle iron from the Eiffel bridge, based on the local approaches supported by the probabilistic ɛa–N or Smith–Watson–Topper (SWT)–N fields [1,2]. This procedure suggests an extension of the fatigue crack propagation model proposed by Noroozi et al. [3,4] to structural details, in order to cover both the fatigue crack initiation and fatigue crack propagation, based on local strain approaches to fatigue. Both fatigue crack initiation and fatigue crack propagation mechanisms are accounted for in the proposed approach. The numerical results are compared with available experimental S-N fatigue data for the notched plate under consideration.

This work addresses the reconstruction of strain gradient fields at the wood growth ring scale from full-field deformation measurements provided by digital image correlation. Moreover, the spatial distribution of the earlywood and latewood radial modulus of elasticity is assessed. Meso-scale tensile tests are carried out on Pinus pinaster Ait. wooden specimens oriented in the radial–tangential plane under quasi-static loading conditions. A parametric analysis of the two-dimensional digital image correlation extrinsic and intrinsic setting parameters is performed, in a balance between spatial resolution and resolution. It is shown that the parametric module is an effective way to quantitatively support the choice of digital image correlation parameters in the presence of the high deformation gradient fields generated by the structure–property relationships at the scale of observation. Under the assumption of a uniaxial tensile stress state, the spatial distribution of the radial elastic modulus across the growth rings is obtained. It is observed that the ratio of the radial modulus of elasticity between latewood and earlywood tissues can vary significantly as a function of the digital image correlation parameters. It is pointed out, however, that a convergence value can be systematically established. Effectively, earlywood and latewood stress–strain curves are obtained and elastic properties are determined assuming the converged digital image correlation setting parameters.

The robustness of the test method based on a single 3D off-axis prismatic specimen for the simultaneous identification of the orthotropic stiffness components of clear wood is addressed. In this method, the specimen is consecutively submitted to uniaxial compression tests along its three orthogonal axes. A data reduction based on anisotropic elasticity is applied to extract active material parameters from 3D full-field deformation measurements provided by stereo-correlation over adjacent faces. Two major limitations of this test method, directly affecting the parameter identification, are analysed and discussed: (1) off-axes angle orientation; (2) friction effects. A numerical study pointed out that radial and tangential rotations of about 29° and 9°, respectively, balances out the strain components in the specimen response. Moreover, friction can be reduced by using mass lubricant or soft material in the contact interface, realising transverse shear deformation.

The non-linear shear behaviour of bovine cortical bone is measured by coupling the Arcan test with digital image correlation. The experimental study is carried out on specimens taken from bovine femur and oriented along the longitudinal-tangential material plane. An ad hoc Arcan fixture is built to transfer the cross-head displacement of the testing machine into a shear loading at the centre of the V-notched section. A validation of predominant shear behaviour at the gauge section is shown from full-field deformation measurements. Moreover, direct evaluation of the shear modulus is obtained by integrating the shear strain component along the V-notches, avoiding numerical correction factors required in the classical data reduction scheme. The shear modulus of bovine cortical bone is found in good agreement with references from literature. Moreover, the shear stress at maximum load is understood as a suitable estimation of the shear strength. Furthermore, the Ramberg�Osgood model is found to provide an accurate description of the non-linear shear behaviour of bone tissue.

Fracture characterization under mode I loading of a cement-based material using the single-edge-notched beam loaded in tree-point-bending was performed. A new method based on beam theory and crack equivalent concept is proposed to evaluate the Resistance-curve, which is essential to determine fracture toughness with accuracy. The method considers the existence of a stress relief region in the vicinity of the crack, dispensing crack length monitoring during experiments. A numerical validation was performed by finite element analysis considering a bilinear cohesive damage model. Experimental tests were performed in order to validate the numerical procedure. Digital image correlation technique was used to measure the specimen displacement with accuracy and without interference. Excellent agreement between numerical and experimental load–displacement curves was obtained, which validates the procedure.

Abstract Mixed-mode I+II fracture characterization of human cortical bone was analyzed in this work. A miniaturized version of the Single Leg Bending test (SLB) was used owing to its simplicity. A power law criterion was verified to accurately describe the material fracture envelop under mixed-mode I+II loading. The crack tip opening displacements measured by digital image correlation were used in a direct method to determine the cohesive law mimicking fracture behavior of cortical bone. Cohesive zone modeling was used for the sake of validation. Several fracture quantities were compared with the experimental results and the good agreement observed proves the appropriateness of the proposed procedure for fracture characterization of human bone under mixed-mode I+II loading.

Assessing wood fracture behavior is essential in the design of structural timber elements and connections. This is particularly the case for connections with the possibility of brittle splitting failure. The numerical cohesive zone models that are used to simulate the fracture behavior of wood make it necessary to assume a cohesive law of the material that relates cohesive tractions and crack opening displacements ahead of the crack tip. This work addresses the determination of the fracture cohesive laws of Eucalyptus globulus, a hardwood species with great potential in timber engineering. This study centres on Mode I fracture loading for RL and TL crack propagation systems using Double Cantilever Beam tests. The Compliance-Based Beam Method is applied as the data reduction scheme in order to obtain the strain energy release rate from the load-displacement curves. The cohesive laws are determined by differentiating the relationship between strain energy release rate and crack tip opening displacement. The latter is measured by the digital image correlation technique. High strain energy release rates were obtained for this species, with no big differences between crack propagation systems. The difference between the crack systems is somewhat more pronounced in terms of maximum stress that determines the respective cohesive laws.

Abstract This work addresses the experimental identification of mode I cohesive law of wood bonded joints. The approach combines the double cantilever beam (DCB) test with both digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. The spectrum geometric mean of the \{FBG\} reflected spectral response was determined, and the wavelength evolution was used to define the fracture process zone (FPZ) development phase. This evaluation allowed a consistent selection of experimental range of over which the identification procedure of mode I cohesive law is build up. Mode I crack length, Resistance-curve and cohesive law parameters are characterised and discussed. The strain energy release rate (GI) is determined from the P�d curve by the compliance-based beam method (CBBM). The crack tip opening displacement (wI) is determined by post-processing displacements measured by DIC. The cohesive law in mode I (sI�wI) is then obtained by numerical differentiation of the GI�wI relationship.

Fracture characterization of human cortical bone under mode II loading was analyzed using a miniaturized version of the end-notched flexure test. A data reduction scheme based on crack equivalent concept was employed to overcome uncertainties on crack length monitoring during the test. The crack tip shear displacement was experimentally measured using digital image correlation technique to determine the cohesive law that mimics bone fracture behavior under mode II loading. The developed procedure was validated by finite element analysis using cohesive zone modeling considering a trapezoidal with bilinear softening relationship. Experimental load-displacement curves, resistance curves and crack tip shear displacement versus applied displacement were used to validate the numerical procedure. The excellent agreement observed between the numerical and experimental results reveals the appropriateness of the proposed test and procedure to characterize human cortical bone fracture under mode II loading. The proposed methodology can be viewed as a novel valuable tool to be used in parametric and methodical clinical studies regarding features (e.g., age, diseases, drugs) influencing bone shear fracture under mode II loading.

A miniaturized version of the double cantilever beam (DCB) test is used to determine the fracture energy in human cortical bone under pure mode I loading. An equivalent crack length based data-reduction scheme is used with remarkable advantages relative to classical methods. Digital image correlation (DIC) technique is employed to determine crack opening displacement at the crack tip being correlated with the evolution of fracture energy. A method is presented to obtain the cohesive law (trapezoidal bilinear softening) mimicking the mechanical behavior observed in bone. Cohesive zone modeling (CZM) (finite-element method) was performed to validate the procedure showing excellent agreement.

Abstract Direct identification of cohesive laws in modes I and İI\} of wood bonded joints is addressed by the double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively. Moreover, the development and extension of fracture process zone (FPZ) ahead of the initial crack tip, is analysed by means of digital image correlation (DIC) and embedded fibre Bragg grating (FBG) sensors. From \{FBG\} spectral response, the spectrum geometric mean is determined and the strain induced by wavelength variation employed to identify the initial and final stages of the FPZ. These stages are used to consistently define the cohesive laws in both modes I and II. Resistance-curves are determined from the compliance-based beam method (CBBM). Besides, the crack tip opening displacements (CTOD) are determined by post-processing displacement field provided by \{DIC\} around the initial crack tip. The strain energy release rate as a function of the \{CTOD\} are then determined for both mode I and mode II. The respective cohesive laws are reconstructed by numerical approximation and differentiation. It is concluded that the proposed data reduction scheme is effective to determine both the \{FPZ\} development phase and the corresponding cohesive laws of wood bonded joints in both mode I and mode II.

Eucalyptus globulus Labill is a hardwood species of broad growth in temperate climates, which is receiving increasing interest for structural applications due to its high mechanical properties. Knowing the fracture behaviour is crucial to predict, through finite element models, the load carrying capacity of engineering designs with possibility of brittle failures such as elements with holes, notches, or certain types of joints. This behaviour can be adequately modelled on a macroscopic scale by the constitutive cohesive law. A direct identification of the cohesive law of Eucalyptus globulus L. in Mode II was performed by combining end-notched flexure (ENF) tests with digital image correlation (DIC) for radial-longitudinal crack propagation system. The critical strain energy release for this fracture mode, which represents the material toughness to crack-growth, was determined by applying the Compliance Based Beam Method (CBBM) as data reduction scheme and resulted in a mean value of 1.54 N/mm.