Electrochemical fatigue crack treatment

Fatigue is responsible for at least 50% of all mechanical and 90% of all metallic failures. Fatigue cracks often start at stress concentrations, and without timely and appropriate remediation, tend to exhibit relatively fast propagation that leads to property damage and sometimes serious accidents. The objective of this research was to develop a new method of fatigue crack treatment in steel structures and estimate its efficiency and limitations. The method was based on placing fatigue cracks under compression by depositing nickel onto the surfaces of the cracks. The proposed method was applied to ASTM E399 compact-tension specimens machined from ASTM A36 steel. This study found that the method was able to arrest fatigue crack propagation. Fatigue crack arrest period varied from 2,000 to 30,000 cycles. The fatigue life of the specimens was extended for up to 55,000 cycles. In many cases the re-initiation life of fatigue cracks after treatment was similar to the crack initiation life obtained from the V-shaped starter notches. A power law relationship was developed that successfully correlates the fatigue crack arrest life and the stress intensity factor range applied for post-treatment load cycling. Fatigue crack packing with nickel resulted in significant reduction of stress concentration factors of the cracks. Spectroscopic analysis confirmed the presence of nickel in electrochemically treated fatigue cracks. The amount of nickel deposited was found to be non-uniform along the length of the cracks. This study found that an elastic finite element analysis (FEA) supported the notion of compressive stresses being developed at the crack tip and of a significant reduction in the stress concentration factor of the fatigue crack due to application of this treatment method. FEA has also supported the expectation that increasing the dosage of crack packing material would tend to result in a longer crack re-initiation period. The proposed method of electrochemical fatigue crack treatment was found to be beneficial in terms of improved corrosion resistance of treated specimens as long as the treatment was uniform and continuous. The average general corrosion rate of nickel-plated ASTM A36 steel specimens that were uncracked was 80% lower than that of the non-plated cases. The discontinuous deposition observed within cracks was expected to promote localized corrosion of the A36 base metal. Future work will examine the use of deposition candidates with less of a tendency toward dissimilar metal corrosion

Design, assembly and experimental tests of a Savonius type wind turbine

The present research project focuses on the development of a Savonius type wind turbine, where a literature review is initially carried out to recognize the appropriate parameters for its design such as turbulence, wind velocity, and air density, followed by a design methodology to achieve the dimensioning by means of resistance calculation and selection of component materials, after having the final concept defined. Using computational tools such as Solidworks, Inventor, Simulation Mechanical, the design stage was validated through simulation to study the dynamic fluid behavior and the components were modeled to evaluate their response to wind loads, verifying their resistance. Subsequently, according to the modeling, the detailed drawings of the components of the turbine were obtained, with which they were assembled. Finally, having the physical model of the Savonius wind turbine, experimental tests were carried out in the laboratory of Fluids and Hydraulic Machines of the Technological University of Pereira

Design, assembly and experimental tests of a Savonius type wind turbine

The present research project focuses on the development of a Savonius type wind turbine, where a literature review is initially carried out to recognize the appropriate parameters for its design such as turbulence, wind velocity, and air density, followed by a design methodology to achieve the dimensioning by means of resistance calculation and selection of component materials, after having the final concept defined. Using computational tools such as Solidworks, Inventor, Simulation Mechanical, the design stage was validated through simulation to study the dynamic fluid behavior and the components were modeled to evaluate their response to wind loads, verifying their resistance. Subsequently, according to the modeling, the detailed drawings of the components of the turbine were obtained, with which they were assembled. Finally, having the physical model of the Savonius wind turbine, experimental tests were carried out in the laboratory of Fluids and Hydraulic Machines of the Technological University of Pereira

Improving the seismic robustness of Conventional Construction concentrically braced steel frames by mobilizing the gravity load framing system

«RÉSUMÉ: Au Canada, le processus de conception de systèmes de reprise des charges sismiques (SRFSs) en acier de faible ductilité de type Constructions Conventionnelles (Type CC) ne demandent pas de conception par capacité et la majorité de la conception peut être effectuée rapidement avec des résultats d’analyses élastiques. Cette méthode de conception simple et rapide représente un grand incitatif aux ingénieurs de conceptions pour choisir ce système. La ductilité limitée de ce système provient de la ductilité inhérente à l’acier et au glissement des connexions pour accommoder les déformations inélastiques et dissiper l’énergie sismique. Le manque de contrôle sur la réponse inélastique et sur la hiérarchie de plastification peut créer des mécanismes de ruine indésirables comme un étage faible ou des ruptures fragiles dans le SRFS.» et «----------ABSTRACT: In Canada, the design process of steel low-ductility Conventional Construction (Type CC) seismic force resisting systems (SFRSs) does not require capacity design and most of the design can be performed quickly based on elastic analysis results. This quick and simple design procedure represents a strong incentive to design engineers for selecting this type of SFRSs. The limited ductility of this system is provided by the inherent ductility of steel and slip in connections to accommodate inelastic deformations and dissipate the seismic energy. The lack of control on the inelastic response and yielding hierarchy can lead to undesirable failure mechanisms such as a soft story or brittle failures in the SFRS.

Numerical Evaluation of Fatigue Crack Growth of Structural Steels Using Energy Release Rate with VCCT

This research presents the numerical evaluation of fatigue crack growth of structural steels S355 and S960 based on Paris’ law parameters (C and m) that are experimentally determined with a single edge notched tension (SENT) specimen using optical and crack gauge measurements on an electromotive resonance machine at constant amplitude load. The sustainable technique is replacing destructive, time-consuming and expensive approaches in structural integrity. The crack propagation is modelled using the 3D finite element method (FEM) with adaptive remeshing of tetrahedral elements along with the crack initiator elements provided in simulation software for crack propagation based on linear elastic fracture mechanics (LEFM). The stress intensity is computed based on the evaluation of energy release rates according to Irwin’s crack closure integral with applied cyclic load of 62.5 MPa, 100 MPa and 150 MPa and stress ratios of R = 0 and 0.1. In order to achieve optimized mesh size towards load cycle and computational time, mesh and re-mesh sensitivity analysis is conducted. The results indicate that the virtual crack closure technique VCCT-based 3D FEM shows acceptable agreement compared to the experimental investigation with the percentage error up to 7.9% for S355 and 12.8% for S960 structural steel

Design for Low-Cost Gas Metal Arc Weld-Based Aluminum 3-D Printing

Additive manufacturing, commonly known as 3-D printing, has the potential to change the state of manufacturing across the globe. Parts are made, or printed, layer by layer using only the materials required to form the part, resulting in much less waste than traditional manufacturing methods. Additive manufacturing has been implemented in a wide variety of industries including aerospace, medical, consumer products, and fashion, using metals, ceramics, polymers, composites, and even organic tissues. However, traditional 3-D printing technologies, particularly those used to print metals, can be prohibitively expensive for small enterprises and the average consumer. A low-cost open-source metal 3-D printer has been developed based upon gas metal arc weld (GMAW) technology. Using this technology, substrate release mechanisms have been developed, allowing the user to remove a printed metal part from a metal substrate by hand. The mechanical and microstructural properties of commercially available weld alloys were characterized and used to guide alloy development in 4000 series aluminum-silicon alloys. Wedge casting experiments were performed to screen magnesium, strontium, and titanium boride alloying additions in hypoeutectic aluminum-silicon alloys for their properties and the ease with which they could be printed. Finally, the top performing alloys, which were approximately 11.6% Si modified with strontium and titanium boride were cast, extruded, and drawn into wire. These wires were printed and the mechanical and microstructural properties were compared with those of commercially available alloys. This work resulted in an easier-to-print aluminum-silicon-strontium alloy that exhibited lower porosity, equivalent yield and tensile strengths, yet nearly twice the ductility compared to commercial alloys