Alfonso Fernández Canteli

Influence of Resin Type on the Delamination Behavior of Carbon Fiber Reinforced Composites Under Mode-II Loading

In this study, the delamination fatigue behavior of two different aeronautical quality composites under mode-II notched flexure loading has been experimentally investigated with the aim of analyzing the effect of the resin type used. Both composites contain the same unidirectional AS4 carbon reinforcement, though embedded in two different matrices: an 8552 epoxy with improved toughness and an unmodified brittle 3501-6 epoxy. The end notched flexure test was found suitable for promoting fatigue delamination under mode-II loading. First, the ΔG-N fatigue curves were determined as the number of cycles necessary for crack onset at a given energy release rate. Then the crack growth rate was obtained for different fractions of the critical energy release rates, Gcr. Calculations of the shear toughness were carried out in accordance with the methods proposed in the ESIS protocol. Critical experimental details are reviewed and the influence of the different procedures proposed for the data assessment of results is analyzed. The results confirm, on the one hand, the influence of the manufacturing process on fatigue crack initiation, and, on the other, the improved performance of the modified resin, both in terms of crack initiation and growth rate.

Business Process Reengineering and University Organisation: A normative approach from the Spanish case

Many of the traditional forms of business are currently being questioned by what is known as business process reengineering (BPR) in the search for improvements in systems of organisation. Reengineering is being positively received within the business world, and could, in theory, be potentially applied to other fields, less traditionally related to business techniques, such as university management. This paper analyses how the university systems (focusing on the Spanish case, currently questioned from various social spheres) should be organised from the point of view of this new methodology, proposing a series of measures and changes for improving the system within the philosophy of BPR.

Probabilistic Weibull Methodology for Fracture Prediction of Brittle and Ductile Materials

In this work, a three-parameter Weibull methodology for fracture prediction of brittle and ductile materials is presented. The approach proposed requires previous definition of the failure criterion to be applied. The parameter estimation is achieved for proportionally and non-proportionally increasing stresses. The case of two concurrent failure types is also handled. The resulting primary failure distribution can be expressed as a function of an effective size (length, area or volume) for its subsequent application in practical design of specimens or components using FEM.

Numerical Simulation of Modified Compact Tension Test Depicting of Experimental Measurement by ARAMIS

The paper is focused on the determination of mechanical fracture parameters from the modified compact tension test applied to the cement-based composites. The experimental measurement was carried out by means of the ARAMIS equipment. The numerical study is performed by ATENA 2D software (based on a cohesive law for crack propagation) taking the material parameters for numerical study from the standard compression test. The experimental and numerical results are discussed and compared with the help of basic fracture parameters and Load – COD (crack open displacement) diagrams.

Evaluation of Concrete Fatigue Measurement Using Standard and Non-Linear Regression Model

The paper deals with the problem of estimating the S-N curve for the cement based composites under fatigue loading. Selected approximation curves for mechanical-fracture parameter values derived from specific fracture energy in time are used to determine the most accurate fatigue parameter values corresponding to the age of specimens when dynamic tests were performed. For standard description of S-N curve the power dependence and Weibull model developed by Castillo et al. are used to discuss the problem under study and the suitability of using models as an input data for finite element modeling

A Design Model for Glass Elements Based on the Statistical Distribution of Crack Sizes

A probabilistic model for the design of building glazing plates of monolithic glass in buildings is presented here. The model is implemented for practical use in Windesign, a computer program developed by the authors. A novel contribution of the model is the consideration of maximal crack sizes as a reference parameter to predict material fracture instead of the critical strengths of the materials, as is usually the case. A sensitivity analysis is also included to assess the relative influence of the different parameters on the model.

The Use of Structural Aluminum for the Design of Large Span Roofs: The Case of the “Cubierta De Oviedo”

The architectural artwork “Cubierta de Oviedo” is located in the Buenavista building complex, it being the movable roof of the City of Oviedo (Asturie, Spain) conference centre. The original design and realization was by the archistar Santiago Calatrava (2004-11). The structure is made in steel. Since the testing of the structure, it was not possible to open the roof. From this occurrence, the idea to design the cubierta in structural aluminum seemed to be a challenge, due to the lowest weight of aluminum as respect to steel. In this perspective, the study focuses on the design of the main beam, spanning 134m total length, with 110m cantilever length, in the most unfavorable condition of open roof. The more appropriate aluminum alloy 7075 has been selected, according to the required mechanical properties. Considering the large height (4.20m) of the cross section, which is a special welded box section, for connecting the component elements, the Friction Stir Welding innovative technique is examined and proposed. The EC9 design codes for aluminum structures is applied with some adaptations due to the peculiarities of the structure. A comparison of steel and aluminum solutions is then presented, in terms of internal forces, mechanical efficiency, deformability, weight and costs, it evidencing the advantages of aluminum for large span roofs.

Effects Of Specimen Size And Crack Depth Ratio On Calibration Curves For Modified Compact Tension Specimens

Abstract The compact tension (CT) test is frequently used to determine fracture properties of metallic materials, such as fracture energy, fracture toughness, crack propagation rate and J-R curves. In the case of cement based composites, a modified compact tension (MCT) specimen can be advantageously used due to the negligible stress concentration arising around the pulling dowel pins during the test. In this work, finite element calculations are used to determine the calibrations curves for the stress intensity factor K, COD, CMOD and CMOD(4), needed for an accurate determination of the fracture parameters, as a function of the ratio a/W. Nominal diameters are selected according to the used core bits between 50 mm and 300 mm.

Evaluation of Conventional Al 2024 Fatigue Limit in Fatigue Test Using Thermographic Measurement: Effect of Frequency

The reliability of the conventional fatigue limit estimation of aluminum alloy Al 2024 provided by thermographic measurements according to the Risitano method is investigated in order to check their validity for practical applications. With this aim, an experimental fatigue program on Al 2024 specimens under load control using a stress ratio R = 0.1 is performed at three different frequencies. The fatigue limit methodologies is first determined according to the methodologies proposed by Risitano et al. and Canteli et al., and then compared with that resulting from the conventional Wöhler curve.

Thermographic Determination Methodology: Application on Fatigue Limit of AL 2024 for R=-1

The application of infrared thermography to obtain the external surface temperature during the application of cyclic loading, allows to evaluate the dynamic behavior of an element and to determine the fatigue limit. In this contribution, the reliability of the fatigue limit provided by the Risitano et al. and Canteli et al. methodologies is investigated in order to check their validity for practical applications. With this aim, an experimental program on aluminium specimens (AL 2024) under load control using a stress ratio minus one is performed. The fatigue limit for AL 2024 is derived, first from the Wöhler curve and then, compared with both Risitano et al. and Canteli et al. methodologies.