Abstract

A local isotropic single parameter scalar model that can simulate the mechanical behaviour of quasi-brittle materials, such as concrete, is described. The constitutive law needs the mechanical characteristics and the fracture energy of concrete to be completely defined. The damage parameter is obtained directly from the value of an equivalent effective stress in order to reduce the computing effort. Due to the unique damage parameter, this model is suitable for the study of quasi-static problems involving monotonically increasing loads. The problem of localisation and mesh dependency have been partially overcome by using an enhanced local method in which a characteristic internal length related to the mesh dimension is employed instead of the characteristic fracture length. In this work, the model was enriched further with the introduction of a shear retention factor that accounts for the friction between the two surfaces of a crack. These new features assure a real improvement of the damage model, maintaining nevertheless its simplicity and low computing cost and making it suitable for the practical solution of large scale problems. Several numerical simulations of experimental tests, concerning fracture tests on concrete specimens and beams failing in shear, have been performed for the validation of the model. The main results from the numerical analyses are described and compared with the experimental ones.

Abstract

Specifically, the use of vinyl ester resins has been studied profusely in both the maritime and industrial sectors and with less time, in the use of reinforcement in civil engineering structures and architecture as passive reinforcements. The resin used in the present work is novel, and still little used. It is vinyl ester resin of bisphenol-A segment modified with urethane. This presents a greater resistance to chemical agents such as those of the petroleum industry, alkaline agents and vapors; together with a lower exotherm that facilitates the manufacture of thick laminates.

A thermal and mechanical characterization has been carried out through the techniques of Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (FTIR) and Thermogravimetry (TGA) of said resin reinforced with high grammage (780 g / cm2) fiber of E glass to evaluate the degradation of the composite and its mechanical properties to the interlaminar shear and bending. The influence of the contact with self-compacting concrete (HAC) on said material, imbedded inside its matrix as a reinforcement, as if it were a passive reinforcement, as well as an accelerated aging study in solution simulating the exudation liquid of the concrete pores (LPH) through said characterization. With the obtained results, it is evaluated and compared, from the point of view of degradation-stiffening vs. mechanical properties, with the traditional Bisphenol-A (VEBA) resins, as well as its suitability for the aforementioned applications, resulting in a resin with better properties than the VEBA.

Abstract

The present work is part of the characterization of glass fiber composites elaborated with a novel vinylester-urethane resin, with addition of poly for use in reinforcing materials for concrete, as a passive reinforcement or as a reinforcement for structures in use, as these resins have a higher Resistance to chemical agents, basics and vapors along with a lower exotherm facilitating the manufacture of thick laminates.Within Mode II fracture mechanics, until this 2014 there was no standard that would collect a procedure to quantify GIIC. Davies through the European Structural Integrity Society (ESIS) issued a mode II test protocol in 1992 known as ENF (End Notch Flexure) [1]ASTM D7905-14 encompasses a fairly complex procedure in which the basis for the characterization of shear fracture toughness in mode II using the final notch flexure (ENF) test is laid.This paper aims to verify the main differences between this classical procedure and the method of this standard to verify their similarities.For this purpose, a mechanical pre-characterization of the reinforced resin is carried out with high-grade fabric (780 g/cm2) with glass fiber E as well as a thinner carbon fiber composite. This characterization is performed by ENF bending tests, and the procedure of the new ASTM D-7905 standard.   [1] ASTM D5528-01, “Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites”, American Society for Testing and Materials, 2001.