Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Heat dissipation and fatigue crack kinetic features of titanium alloy Grade 2 after laser shock peening
Get PDFThe work is devoted to experimental investigation of the laser shock peening (LSP) effect on fatigue crack propagation rate and heat dissipation at the crack tip in specimens made of titanium alloy Grade 2 with a stress concentrator. It is shown that the LSP can leads both to positive and negative effect on fatigue lifetime. The effective processing scheme, which includes stress concentrator zone, was proposed. This type of treatment forms an optimal residual stress field, which slows down the crack initiation and propagation processes. The effective LSP processing scheme reduces the value of the stress intensity factor and, as a consequence, effects on an intensity of plastic deformation at the crack tip. This effect can be visualised by measurement of heat flux from the crack tip area. Both heat flux from the crack tip and crack rate are less in the LSP processed specimens. Structural investigations of LSP treated material near fatigue crack path have shown that structural defects (twins) that appear on the surface of the material as a result of LSP do not have a significant effect on the fatigue crack propagation, and the configuration of the residual stresses field created by LSP plays a decisive role
Influence of hBN and MoS2 fillers on toughness and thermal stability of carbon fabric-epoxy composites
Get PDFHexagonal boron nitride (hBN) and molybdenum disulfide (MoS2) fillers of 2 to 8 wt.% influence on toughness, microhardness and thermal stability of carbon fabric-reinforced epoxy composite (CFREC) reported. Mode-I, mixed-mode I/II toughness and microhardness of CFREC improved due to the addition of hBN and MoS2 separately upto 6 wt.% filler loading. The epoxy matrix in CFREC modified by hBN and MoS2 strengthens the matrix, deflects the crack path and resists delamination. Toughness reduced beyond 6 wt.% filler addition due to agglomeration and poor fiber-filler-matrix bonding as revealed by the surface morphology of the fracture specimen. Thermal analysis reveals decomposition temperature at 25% weight loss increased from 395 to 430 °C and 395 to 411 °C due to 4 wt.% MoS2 and 4 wt.% hBN addition to CFREC respectively. Impermeable characteristics of MoS2 and hBN fillers caused tortuous diffusion path for gas molecules and delayed thermal decomposition
Optimization of the Mechanical Property of Friction Stir Welded Heat Treatable Aluminum Alloy by using Bio-Inspired Artificial Intelligence Algorithms
No full textThe concepts and inspiration of biological evolution in nature are used to create new and effective competing tactics in the burgeoning field of bio-inspired computing optimization algorithms. In the present work, nine specimens of similar alloys i.e., AA6262 were Friction Stir Welded. Spindle Speed (RPM), Traverse Speed (mm/min), and Plunge Depth (mm) were the input parameters while the Ultimate Tensile Strength (MPa) was an output parameter. The main objective of the work is to obtain the maximum optimized Ultimate Tensile Strength (MPa) by using Bio-Inspired Artificial Intelligence Algorithms i.e., Differential Evolution and Max Lipschitz optimization (Max LIPO) Algorithm. The results showed that the Differential Evolution algorithm resulted in a slightly higher value of the Ultimate Tensile Strength in comparison to the Max LIPO algorithm
Analysis of the adhesive damage for different shapes and types patch’s in Aircraft Structures corroded with an inclined crack
Get PDFIn this study, the finite element method is used to analyze the effect of corrosion and the behavior of inclined cracks of an aluminum plate Al 2024 -T3 under thermomechanical loading. The effects of the inclination of the crack and the effect of temperature for and different types and shapes of adhesives are highlighted. The results obtained show the increase of the crack inclination leads to a decrease of the damaged area and the damaged area ratio of the adhesive. In addition, the ratio DR increases with increasing temperature variation ΔT. The best performing patch shape that gave interesting results during this analysis is the circular and for type the Boron/epoxy is the best
PVC failure modelling through experimental and digital image correlation measurements
Get PDFThis paper analyses industrial PVC sheets structural integrity assessment widely used for different ranges of industrial applications. We investigated combined approaches focused on fracture toughness assessment to predict PVC mechanical behavior against failure. We ran a series of tests on tensile and single-edge notched samples at various crosshead speeds on a tensile test machine. PVC sheets' stress intensity factors were evaluated using both theoretical and experimental approaches to model crack growth. In the experimental procedure, we used the digital image correlation (DIC) method. We also developed a semi-empirical model to predict crack length over time. Furthermore, we proposed that the crack growth rate and stress intensity factor were satisfactorily correlated at all crosshead speeds and that the crack growth rate could be represented using a power-law model. In pre-cracked PVC specimens, the results showed that crack growth appears to be influenced by crosshead speed
Review of Current Developments on High Strength Pipeline Steels for HIC Inducing Service
Get PDFNowadays, an increasing number of oil and gas transmission pipes are constructed with high-strength low alloy steels (HSLA); however, many of these pipelines suffer from different types of hydrogen damages, such as hydrogen-induced cracking (HIC). So many research efforts are being carried out to reduce the detrimental effects of hydrogen damage in HSLA steel pipes.
The thermomechanical control process (TMCP) is a microstructural control technique that is able to eliminate the conventional heat treatment after hot rolling. Recent research demonstrated that TMCP provides high HIC resistance without adding high amounts of alloying elements or expensive heat treatments. However, once these HSLA steel pipes are put into service, they experience HIC damage, and the prediction of its kinetics is a necessary condition to perform Fitness-For-Service assessments. To develop a reliable predictive model for the kinetics of HIC, the relations among the microstructural features, environmental parameters, and mechanical properties have to be fully understood.
This paper presents a review of the key metallurgical and processing factors to develop HSLA steel pipes, as well as a review of the phenomenological and empirical models of HIC kinetics in order to identify specific research directions for further investigations aimed to establish a reliable and sound model of HIC kinetics.
 
Fatigue growth rate of inclined surface cracks in aluminum and titanium alloys
Get PDFIn this paper the fatigue crack growth tests were carried out on surface-crack tension (SCT) specimens, made of 7050 and Ti6Al4V alloys, with initial semi-elliptical surface cracks. Pure Mode I conditions were realized on SCT specimens with crack plane located orthogonal to the loading direction, while Mixed-mode conditions were observed on SCT specimens with inclined crack. Optical microscope measurements and the crack mouth opening displacement (CMOD) method were respectively used to monitor crack length and calculate crack depth. Current crack shape during the tests was highlighted by alternation of loading spectrum with baseline load block and a marker load block. The stress strain field along the crack front of semi-elliptical cracks in the SCT specimens was assessed by Finite Element Method (FEM) analysis. The stress intensity factors (SIFs) were calculated along crack fronts and equivalent elastic SIF formulation was used for crack growth rate assessment under mixed mode conditions. As a result, the fracture resistance parameters of aluminum and titanium alloys were obtained for two crack propagation directions under Mode I and Mixed-mode loading. The benefits of using the computational and experimental results of SCT specimen for the assessment of the surface crack growth rate in aluminum and titanium alloys under Mixed-mode loading conditions were stated
Investigation of the Effect of Yarn Waste Fibers and Cocamide Diethanolamide Chemical on the Strength of Hot Mix Asphalt
Get PDFIn this study, conventional bitumen test were performed on bituminous binder modified with Cocamide Diethanolamide chemical at different ratios. According to results of tests, the most suitable additive ratio has been determined as 5%. However, it was concluded that indirect tensile strength and resistance to moisture of samples prepared with bituminous binder modified with 5% Cocamide Diethanolamide has been adversely affected. It was desired to investigate that whether these properties could be strengthened by yarn waste fibers. Firstly, the effect of 0.1%, 0.2% and 0.3% yarn waste fibers on samples prepared with reference bituminous binder was investigated. Obtained results showed that both indirect tensile strength and resistance to moisture of samples containing 0.1% yarn waste fiber increased. Therefore, 0.1%, 0.2% and 0.3% yarn waste fibers were added to the aggregate mixture and mixing of them with bituminous binder modified with 5% Cocamide Diethanolamide were provided. According to obtained results, different ratios of yarn waste fibers added to aggregate mixture did not have a positive effect on moisture sensitivity. Tensile strength ratio values of samples containing bituminous binder modified with 5% Cocamide Diethanolamide and yarn waste fibers added to the aggregate mixture did not provide specification limit
Seismic vulnerability analysis of reinforced concrete frame with infill wall considering in-plane and out-of-plane interactions
Get PDFThe seismic performance of a building hinges on the seismic capacity and damage features of the reinforced concrete (RC) frame with masonry infill walls. To reasonably evaluate the seismic performance and seismic economic loss of masonry infill walls, it is necessary to consider the in-plane (IP) and out-of-plane (OOP) interactions of these walls under seismic actions, and to model the vulnerability of the infill walls and the frame. Based on the test data on masonry infill walls, this paper designs a performance indicator for infill wall in the light of IP-OOP interactions, and determines the response threshold of each damage state. With the aid of OpenSees, the authors developed and verified a reasonable modeling method for RC frames with infill walls. As per the current code in China, a 5-storey RC frame with infill walls was designed, and two three-dimensional (3D) space models were established for the structure by the proposed modeling method. One of them considers IP-OOP interactions, and the other does not. Then, the structure was subjected to incremental dynamic analyses (IDA), and different damage indicators were determined to examine the damage of the infill walls and the overall structure, producing a set of vulnerability curves. The results show that the consideration of IP-OOP interactions significantly increases the probability of seismic damages on the infill walls and the overall structure. The most prominent increase was observed in the medium to serious damage stages
Experimentally evaluation of high-performance concrete mixes used for tunnels and containing silica fume and polypropylene fiber after exposed to high temperatures
Get PDFThis work introduces an experimental study to evaluate the effect of elevated temperatures on the mechanical properties of high-performance concrete (HPC) mix with changes in Water-Cementitious ratios, W/(C+SF), Silica Fume percent, SF, and Polypropylene, PP, fiber contents. This mix was typically designed to satisfy the requirements of tunnel concrete. The compressive and indirect tensile strengths were measured at room temperature, RT, and after exposure to 400°C and 800°C. Moreover, SEM micrograph and EDS spot analysis tests were done to evaluate the effect of elevated temperatures. Fifteen mixes of HPC with different ratios of W/(C+SF), SF, and PP fiber were tested. According to the test results, the compressive strength values of design mixes increased significantly after exposure to 400°C. Moreover, using SF = 10%, the results indicated remarkable improvements in the compressive strength at 400°C and 800°C, in the case of the W/(C+SF) ratio of 0.31. On the other hand, the highest effect of the presence of PP fibers was 0.211, depending on variable ratios of the W/(C+SF) ratio and the SF content. In the case of PP=0.106 and SF=10%, the mass loss was higher at exposure to temperatures of 800°C