Lucio Nobile

Detection of crack location using cracked beam element method for structural analysis

The local flexibility introduced by cracks changes the dynamic behavior of the structure and, by examining this change, crack position and magnitude can be identified. In order to model the structure for FEM analysis, a special finite element for a cracked Timoshenko beam is developed. Shape functions for rotational and translational displacements are used to obtain the consistent mass matrix for the cracked beam element. Effect of the crack on the stiffness matrix and consistent mass matrix is investigated. Proposed is a procedure for identifying cracks in structures using modal test data.

Mixed mode crack initiation and direction in beams with edge crack

The S-theory is applied to determine crack initiation and direction for beams with edge crack. A simple method for obtaining approximate stress intensity factors of straight cracked beams is also proposed. It takes into account the elastic crack tip stress singularity while using the elementary beam theory. The results are in reasonable agreement with the more accurate calculations.

Seismic Vulnerability Assessment of a Historical Church: Limit Analysis and Nonlinear Finite Element Analysis

The seismic vulnerability of a historical Basilica church located in Italy is studied by means of limit analysis and nonlinear finite element (FE) analysis. Attention is posed to the failure mechanisms involving the facade of the church and its interaction with the lateral walls. In particular, the limit analysis and the nonlinear FE analysis provide an estimate of the load collapse multiplier of the failure mechanisms. Results obtained from both approaches are in agreement and can support the selection of possible retrofitting measures to decrease the vulnerability of the church under seismic loads.

Crack initiation behaviour of orthotropic solids as predicted by the strain energy density theory

The strain energy density theory is applied to determine crack initiation in orthotropic solids. An approach is used to derive the complex variable expressions of the elastic fields. The formulation is used to solve the boundary value problem by superimposing of Mode-I and Mode-II crack problems. It is shown that asymptotic expressions of the crack tip stress and displacement fields are affected by non-singular terms related to biaxial loading.

On the inclined crack problem in an orthotropic medium under biaxial loading

Abstract The problem of an inclined crack in an orthotropic medium under biaxial loading is analyzed. A suitable coordinate transformation is introduced and two decoupled systems of the Cauchy–Riemann type are obtained in terms of complex potentials. The crack problem is solved by using the method of analytic continuation and closed form expressions of the near tip stress and displacement fields are derived. The influence of load biaxiality on the stress intensity factors, as well as on the local stress components is studied and graphically represented. Moreover, the action of material orthotropy on various quantities describing the crack characteristic is pointed out.

Mixed mode crack growth in curved beams with radial edge crack

Mixed mode crack growth in curved beams with radial edge crack is predicted by the prominent S-theory. An improved simple engineering method for obtaining approximate stress intensity factors of curved cracked beams is also used. It takes into account the elastic crack tip stress singularity while using the elementary beam theory. The results are in reasonable agreement with the more accurate calculations in literature.

EXPERIMENTAL ANALYSIS OF TENSILE PROPERTIES OF SOME SUTURING MATERIALS

The aim of the investigation is to quantitatively evaluate the failure load of several suture materials currently used in dentistry surgery. No chromic catgut, silk, Prolene, Ethilon, Ethibond, Vicryl and Vicryl Rapid, obtained from Ethicon s.p.a., in the sizes 3–0, 4–0, and 5–0 have been tested. The analysis has been carried out measuring the diameter of each suture with an optical microscope to determine the accuracy of manufacturers’ data. Tensile testing has been performed to evaluate the failure load of each material. Finally, sutures of the same effective diameter class have been compared relative to failure load. Results show that monofilament sutures present a failure load remarkably superior to that of multifilament sutures. Using SEM analysis monofilament sutures present less surface irregularities than multifilament sutures. Only monofilaments Ethilon 4–0 and 5–0, Prolene 4–0, and multifilament no chromic catgut 4–0 and 5–0 meet the requirements of the Italian Pharmacopeia. In contrast, Prolene 5–0 and the other multifilaments, silk, Ethibond, Vicryl and Vicryl rapid, have a larger diameter than that declared on the label by the producer.

A simplified approach for ceramic fracture toughness evaluation by indentation

Abstract The application of the Vickers indentation test for fracture toughness determination in brittle materials has become widespread because of the simplicity of the test. The undoubted advantages of this technique are counterbalanced by the multitude of complex models and related equations reported in the literature. In this paper, a simplified and more realistic approach for estimating fracture toughness in brittle materials is presented. The proposed model has been applied to soda-lime glass evidencing substantial agreement with other conventional standard methods.

Three Dimensional Frame Structures with Edge-Cracks of Uncertain Depth and Location

In this paper, a numerical study on the structural behaviour of three-dimensional cracked structures have been presented. The stiffness matrix of the cracked element is found as the inverse of the compliance matrix. This matrix is given by the sum of the compliance matrix of the intact element and an additional compliance matrix which contains all the flexibilities given by the presence of the crack. The flexibilities are related to the stress intensity factors. A simple method for obtaining approximate stress intensity factors is applied. It takes into account the elastic crack tip stress singularity while using the elementary beam theory. Moreover, crack depth and location are modelled as random variables in order to take into account the unavoidable uncertainty that always affects damaged structures. A simple and accurate method for the probabilistic characterization of the linear elastic response of cracked structures with uncertain damage is employed. According to this method, the uncertainties are transformed into superimposed deformations depending on the distribution of internal forces and an iterative procedure is established to solve the resultant equations. Numerical tests evidence excellent accuracy for multicracked structures with large fluctuation of damage. Present manuscript also discusses relevant patents.

Numerical Investigation on the Crack Propagation in a Flat Stiffened Panel

This work is focussed on the numerical prediction of the fracture resistance of a flat fullscale aluminium alloy 2024 T3 stiffened panel under monotonic traction loading condition. The numerical simulations are based on the micromechanical Gurson-Tvergaard (GT) model for ductile damage. The applicability of the GT model to this kind of structural problem has been studied and assessed by comparing numerical results, obtained by using the WARP 3D finite element code, with experimental data provided from literature.