Fatigue Crack Growth Assessment and Fatigue Resistance Enhancement of Aluminium Alloys

Fatigue damage of aluminium alloys is one of the key concerns in transport industries, particularly in the aerospace industry. The purpose of the project is to develop new knowledge and techniques against fatigue failure for these industries through a systematic investigation of fatigue resistance and crack growth behaviours of aluminium alloys. Fatigue and fracture mechanics have been investigated analytically, numerically and experimentally in this project. Overload transient effect on fatigue crack growth has been examined by considering various parameters including crack closure, overload ratio (OLR), load ratio ( ratio), baseline stress intensity factor range, (∆ ) and geometry. It was found that crack closure can be correlated qualitatively and quantitatively to all other parameters associated with overload transient behaviour. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve can be separated to obtain reliable crack closure measurement. In this project, different methods are used to better understand the transient retardation process so that the damage tolerance design (DTD) of the components made of aluminium alloys can be enhanced. Another important parameter for fatigue and damage tolerance design (DTD) of engineering components is the threshold stress intensity factor range for fatigue crack growth, ∆ ℎ. A small variation in identification of ∆ ℎ can lead to a big change in overall estimation of fatigue life. In this project, an analytical model has been developed for aluminium alloys by fitting an analytical curve with raw crack growth data in order to identify the ∆ ℎ. This model has the capacity to identify ∆ ℎ for different aluminium alloys at various ratios. There is a great demand for enhanced fatigue life of aluminium alloys in the transport industry. This project has carried out a detailed investigation of electromagnetic treatment (ET) in the form of electropulsing treatment to develop an efficient technique for fatigue resistance enhancement. ET parameters including the treatment intensity, treatment time and the number of applications have been optimised. It is suggested that the duration of ET treatment can be used as the main parameter among all these to control the fatigue resistance of the aluminium alloy. The improvement in fatigue resistance has been explained by the change in microhardness and conductivity of aluminium alloy due to ET. Additionally, the fracture morphology was analysed using scanning electron microscopy (SEM). The precipitates and dislocation characteristics were also studied using transmission electron microscopy (TEM). The outcomes of this investigation will help improve structural integrity by enhancing fatigue resistance of aluminium alloys

Effect of Electromagnetic Treatment on Fatigue Resistance of 2011 Aluminum Alloy

Beneficial effects of the electromagnetic treatment on fatigue resistance were reported on several engineering alloys. These could be linked to the dislocation activity and the rearrangement of the crystal structure of the material under the electromagnetic field (EMF), resulting in delayed crack initiation. This paper presents an experimental study on the effect of pulsed electromagnetic treatment on the fatigue resistance of 2011 aluminum alloy. Circular cantilever specimens with loads at their ends were tested on rotating fatigue machine SM1090. Fatigue lives of treated and untreated specimens were analyzed and compared systematically. It has been found that the effect of the pulsed electromagnetic treatment on the fatigue resistance is dependent on the intensity of the pulsed EMF and the number of the treatment applied. Clear beneficial effect of the pulsed electromagnetic treatment on the fatigue resistance of the aluminum alloys has been observed, demonstrating a potential new technique to industries for fatigue life extension

Improved corrosion and cavitation erosion resistance of laser-based powder bed fusion produced Ti-6Al-4V alloy by pulsed magnetic field treatment

The application of pulsed magnetic field (PMF) treatment demonstrated enhanced corrosion resistance in saline solution and prolonged resistance to cavitation erosion in deionised water for Ti-6AI-4V alloy manufactured by laser-based powder bed fusion (LPBF) and conventional wrought processing methods. The observed outcomes were attributed to the formation of a denser protective surface oxide layer and microstructural changes, resulting in a reduction of the α' phase by 0.13% and an increase in the presence of dislocations at the surface. Consequently, this led to an increase in the compressive residual stresses. Additionally, the application of this treatment resulted in the formation of highly refined and uniform precipitates, leading to a notable enhancement in microhardness by 5.73% and 5.85% for the conventionally manufactured (CM) and LPBF samples, respectively

Improved corrosion and cavitation erosion resistance of laser-based powder bed fusion produced Ti-6Al-4V alloy by pulsed magnetic field treatment

The application of pulsed magnetic field (PMF) treatment demonstrated enhanced corrosion resistance in saline solution and prolonged resistance to cavitation erosion in deionised water for Ti-6AI-4V alloy manufactured by laser-based powder bed fusion (LPBF) and conventional wrought processing methods. The observed outcomes were attributed to the formation of a denser protective surface oxide layer and microstructural changes, resulting in a reduction of the α’ phase by 0.13% and an increase in the presence of dislocations at the surface. Consequently, this led to an increase in the compressive residual stresses. Additionally, the application of this treatment resulted in the formation of highly refined and uniform precipitates, leading to a notable enhancement in microhardness by 5.73% and 5.85% for the conventionally manufactured (CM) and LPBF samples, respectively

Using mentimeter to enhance learning and teaching in a large class

Mentimeter is a web-based Clicker, Audience Response System (ARS) or Student Response System (SRS) which allows students to answer digital questions using a mobile device. It has the potential to transform the classroom environment into a more interactive, engaging and inclusive one. In this paper, a brief literature review has been provided which addresses the benefits of using ARS including Mentimeter in a large class. Additionally, the mechanics behind how the workings of the Mentimeter, its features and applications have been evaluated in order to offer the instructors with the insights about using Mentimeter for their own practice. Finally, a case study has been explained where Mentimeter was used for the formative assessment. In the present study, a Mentimeter formative assessment model has been developed which can be implemented as a good practice in Higher Education (HE). A survey on perception of students about using Mentimeter has been assessed and from the results, it is evident that using Mentimeter has a positive impact on students’ attitude and performance, learning environment and technical aspects. These results will be further discussed by linking pedagogical theories and its benefits

Effect of plastic deformation on compliance curve based crack closure measurement

Fatigue crack growth depends heavily on near tip stress-strain behavior controlled by many micromechanical and microstructural factors. Crack closure is widely used to rationalize crack growth behaviour under complex loading conditions. Reliable crack closure measurement is essential for enhanced damage tolerance design and remains a challenge to the industry. This paper focuses on the effect of plastic deformation ahead of a notch/crack on the non-linearity of compliance curves of 6082-T651 aluminium alloy specimens to highlight a potential issue in the conventional compliance curve based crack closure measurement technique. Experimental and numerical simulation results demonstrate that plastic deformation ahead of the notch will introduce non-linear stress-strain behavior in the absence of crack closure. It is proposed that the effect of crack tip plasticity on the non-linearity of the compliance curve be separated to obtain reliable crack closure measurement

Performance analysis of a gas turbine engine via intercooling and regeneration- Part 2

The current study aims to amplify the predictive ability of the numerical model developed for a gas turbine engine-based power plants by process of regeneration and intercooling. Artificial neural networks (ANN) and adaptive neuro-fuzzy interface systems (ANFIS) are the two techniques mainly concentrated in this study which were not properly implemented previously. The performance parameters namely, specific power (SP), thermal efficiency (η), and enthalpy based specific fuel consumption (EBSFC) of a Turboprop engine were predicted using thermodynamic parameters namely, pressure ratio (PR), nozzle pressure ratio (NPR), turbine inlet temperature (TIT), for constant regeneration (R), and intercooling (E) efficiencies. The results showed that a high regression result R2 of 0.9831 and 0.9899was found for the ANFIS model for η for training and testing, respectively. Also, the ANFIS model resulted in best performance of the performance characteristics when compared to ANN

Heat transfer of Ca (NO3)2‑KNO3 molten salt mixtures for austempering and martempering processes of steels

Molten salts are highly effective as a quenching medium for austempering and martempering processes, enabling precise control of cooling rates to achieve the desired microstructures and mechanical characteristics in steel components. One such promising molten salt is a multicomponent Ca (NO3)2-KNO3 molten salt. The current work explores the cooling severity of molten Ca (NO3)2-KNO3 mixtures, which are commonly used for such purposes. The said mixture, with varying concentrations and bath temperatures was used for quenching the Inconel probe with thermocouples. The temperature data extracted was used to determine the transient heat flux developed at the metal−quenchant interface. A set of critical points were assessed against the peak heat extraction rates. Additionally, the fluctuation of mean heat flux and surface temperature in relation to these crucial points were plotted, along with changes in composition and bath temperature of the quench media. The cooling intensity of these quench solutions, as measured by Inconel probes, correlated well with the average hardness values observed in steel probes. The level of homogeneity in heat transmission, as measured by the spatial variance of the normalized heat energy, decreased as the percentage of KNO3 in the quench medium increased