Papers by Author: Paulo Roberto Cetlin

Abstract: The performance of materials made from Portland cement is usually evaluated by tensile strength under compression loads, elastic modulus and porosity. Modulus of elasticity is usually determined from compression tests, and the results show large dispersions. With the advances in data acquisition and signal processing, the infrared thermography and forced resonant frequency have been increasingly used in the study of materials. However, these studies are devoted almost entirely to metals. In this paper it is evaluates the use of the method of forced longitudinal resonance frequency and infrared thermography as a tool for characterization of the buildings cementitious materials. The results show that thermography and forced resonant frequency are Able to detect changes in concrete macrostructure as well as the nature of its constituents.

Abstract: One of the most significant aspects of the axisymmetric drawing operation is the occurrence of non-homogeneous deformation in the cross section of the metal. This phenomenon is associated with an internal distortion process that takes place in the bar as it flows through the die, leading to the development of higher drawing forces and affecting the subsequent mechanical behavior of the material. An adequate analysis of the process and of the work hardening of the drawn metal, therefore, must involve a detailed study of the deformation features in the forming operation. In the present work, the deformation in the single-pass drawing of AISI 304 stainless steel bars was investigated through the evaluation of the relationship between the redundant deformation factor and the parameter . Two experimetal procedures were employed in the study: the visioplasticity and the stress-strain curves superposition techniques. The first one, previously considered as the method leading to the most realistic solutions to various forming processes, allowed the establishment of an increasing linear relationship between de redundant deformation factor and the parameter . A similar behavior was observed through the stress-strain curves superposition technique. In this case, however, the redundant deformation factor values were lower or higher than those obtained through visioplasticity according to the drawing conditions and more sensitive to variations of the parameter . The results were compared to those exhibited by the AISI 420 stainless steel, revealing the influence of the structural features on the behavior of the metal.

Abstract: The strain paths followed by metals during sheet forming can be quite complex, especially when successive forming steps are involved. The work hardening of metals associated with these strain paths differs from that caused only by monotonic straining, such as simple tension or compression. It is important to have an adequate description of the work hardening of the material under processing, especially when numerical simulations of the forming are used. The experimental evaluation of the effect of strain path changes on the material work hardening is usually performed through tensile testing following the strain path changes. This technique, however, demands complex machining operations of the formed sheets and the imposed strain is severely limited by impending necking. The present paper utilizes simple shear as a tool for the determination of the work hardening of CuZn34 brass sheets following various strain path changes associated with combinations of different modes of deformation such as rolling, tension, cyclic and forward shears. The results indicate that the cyclic shearing delays the occurrence of plastic instabilities for brass previously tensioned, occurring the opposite for final monotonic shearing. These phenomena were correlated with the probable microstructural evolution of the CuZn34 brass.

Abstract: Surface defects are an inevitable characteristic of the raw material employed in the drawing of copper wires. These defects may cause problems in the processing of the material, both during the drawing down to wires and in the final manufacturing of artifacts with the produced wire. The literature reports few analyses covering the importance of these initial defects, as well as concerning their evolution or eventual healing during the drawing. The present paper presents such an analysis for a 12.7 mm diameter copper bar displaying artificial defects 1mm wide and 0.3mm deep. Low angle drawing led to the almost complete healing of the defect after three drawing passes with a 10% reduction of area each. The use of a high semi-angle die led to a completely different situation, where no such defect healing was observed.