Determination of the yield loci of four sheet materials (AA6111-T4, AC600, DX54D+Z, and H220BD+Z) by using uniaxial tensile and hydraulic bulge tests)

In sheet metal forming simulation, a flow curve and a yield criterion are vital requirements for obtaining reliable numerical results. It is more appropriate to determine a flow curve by using biaxial stress condition tests, such as the hydraulic bulge test, than a uniaxial test because hardening proceeds higher strains before necking occurs. In a uniaxial test, higher strains are extrapolated, which might lead to incorrect results. The bulge test, coupled with the digital image correlation (DIC) system, is used to obtain stress–strain data. In the absence of the DIC system, analytical methods are used to estimate hardening. Typically, such models incorporate a correction factor to achieve correlation to experimental data. An example is the Chakrabarty and Alexander method, which uses a correction factor based on the n value. Here, the Chakrabarty and Alexander approach was modified using a correction factor based on normal anisotropy. When compared with DIC data, the modified model was found to be able to better predict the hardening curves for the materials examined in this study. Because a biaxial flow curve is required to compute the biaxial yield stress, which is an essential input to advanced yield functions, the effects of the various approaches used to determine the biaxial stress–strain data on the shape of the BBC2005 yield loci were also investigated. The proposed method can accurately predict the magnitude of the biaxial yield stress, when compared with DIC data, for all materials investigated in this study

Accurate descriptions of the ansiotropic plastic yielding behaviour of various metallic sheets.

This thesis focuses on two vital requirements - yield criterion and flow curve - to obtain reliable numerical results in sheet metal forming simulations. First, this thesis generally aims to explore the potential accuracy of the Taylor models, namely the full constraint and pancake, for replacing complicated mechanical tests involved in the defining process of advanced yield functions for aluminium alloys. The exploration process resulted in a simple and efficient yield locus description denoted as CTF. This model correlates with the texture-based model (Taylor full constraint) and the phenomenological model (BBC2005) for the considered aluminium alloys. Based on this newly proposed model (CTF), a hybrid solution, denoted as Method II, is suggested. Consequently, the demands associated with the extensive and difficult tests required for calibrating the advanced yield function can be reduced. A remaining issue related with the identification procedure of the plastic anisotropy parameters associated with advanced yield criteria was addressed in this thesis by applying the trust region approach for identifying the material coefficients, and its performance was compared with the line-search approach. The applied algorithms were tested for various aluminium and steel alloys with different levels of anisotropy. Second, this research sought to develop an accurate determination of the biaxial flow curve for various aluminium and steel alloys when a continuous and in-line thickness measurement system, such as the digital image correlation (DIC) system, is absent. In certain sheet metal forming processes, it is more appropriate to determine a flow curve using biaxial stress condition tests, such as the hydraulic bulge test, than a uniaxial test because hardening proceeds higher strains before necking occurs. In a uniaxial test, higher strains are extrapolated, which might lead to erroneous results. Usually, the bulge test coupled with the DIC system is used to obtain stress–strain data. In the absence of the DIC system, analytical methods are instead employed to estimate hardening. Typically, such models incorporate a correction factor to achieve correlation with the experimental data. An example is the Chakrabarty and Alexander method that utilises a correction factor based on the n-value. Here, the Chakrabarty and Alexander approach was modified with a correction factor based on normal anisotropy. When compared with DIC data, the modified model was found to be able to predict the hardening curves better for the materials examined in this study. Based on the fact that a biaxial flow curve is required to compute the biaxial yield stress, an essential input to advanced yield functions, the effects of various approaches to biaxial stress–strain data on the shape of the BBC2005 yield loci were also investigated. The proposed method could accurately predict the magnitude of biaxial yield stress, when compared with DIC data, for all materials that were investigated in this study

Characterization of the Vibration and Strain Energy Density of a Nanobeam under Two-Temperature Generalized Thermoelasticity with Fractional-Order Strain Theory

In this work, fractional-order strain theory was applied to construct a novel model that introduces a thermal analysis of a thermoelastic, isotropic, and homogeneous nanobeam. Under supported conditions of fixed aspect ratios, a two-temperature generalized thermoelasticity theory based on one relaxation time was used. The governing differential equations were solved using the Laplace transform, and their inversions were found by applying the Tzou technique. The numerical solutions and results for a thermoelastic rectangular silicon nitride nanobeam were validated and supported in the case of ramp-type heating. Graphs were used to present the numerical results. The two-temperature model parameter, beam size, ramp-type heat, and beam thickness all have a substantial influence on all of the investigated functions. Moreover, the parameter of the ramp-type heat might be beneficial for controlling the damping of nanobeam energy

Fracture Toughness and Fatigue Crack Growth Analyses on a Biomedical Ti-27Nb Alloy under Constant Amplitude Loading Using Extended Finite Element Modelling

The human body normally uses alternative materials such as implants to replace injured or damaged bone. Fatigue fracture is a common and serious type of damage in implant materials. Therefore, a deep understanding and estimation or prediction of such loading modes, which are influenced by many factors, is of great importance and attractiveness. In this study, the fracture toughness of Ti-27Nb, a well-known implant titanium alloy biomaterial, was simulated using an advanced finite element subroutine. Furthermore, a robust direct cyclic finite element fatigue model based on a fatigue failure criterion derived from Paris’ law is used in conjunction with an advanced finite element model to estimate the initiation of fatigue crack growth in such materials under ambient conditions. The R-curve was fully predicted, yielding a minimum percent error of less than 2% for fracture toughness and less than 5% for fracture separation energy. This provides a valuable technique and data for fracture and fatigue performance of such bio-implant materials. Fatigue crack growth was predicted with a minimum percent difference of less than nine for compact tensile test standard specimens. The shape and mode of material behaviour have a significant effect on the Paris law constant. The fracture modes showed that the crack path is in two directions. The finite element direct cycle fatigue method was recommended to determine the fatigue crack growth of biomaterials

Finite Element Simulation of the Effect of Phase Transformation on Residual Stress in a Thick Section T-Joint

It has long been known that residual stresses can profoundly affect the integrity of engineering components. Evidence has recently emerged to confirm that solid-state phase transformations in steels can significantly influence the as-welded residual stresses. A two-dimensional thermo-mechanical, generalized plane strain finite element model was created to simulate the effect of phase transformation on residual stress during the multi-pass weld process in a thick section T-joint. The effect of phase transformation and martensite start temperatures was investigated. The results showed that phase transformation generated compressive residual stress underneath the last bead to be deposited for this multi-pass weld model. However, some constraints around the bead were essential to provide that stress. Tensile residual stress was generated in the bulk of the weld area when phase transformation was considered. Therefore, phase transformation may be helpful for single pass and other groove welds but may be unhelpful in the case of the T-joint examined here. The effect of the martensite start temperature is small compared with the main difference between having a phase transformation and not having one

Effects of Metal Fasteners of Ventilated Building Facade on the Thermal Performances of Building Envelopes

Thermal bridging in the building envelope is one of the main causes of energy losses, even in high-efficiency ventilated building façades. In this study, the effects of point-thermal bridges attributed to metal fasteners on the heat transferred through different types of bricks were predicted. All the structural details of the substrate wall were included as well. This was accomplished with a multi-scale, finite element modelling approach used to enhance the thermal insulation efficiency of the building envelope. The effects of the metal fastener length, diameter, density and location were examined to elucidate any opportunity to minimize the heat losses caused by thermal bridging. The results demonstrated that increases in the lengths of fasteners yielded higher energy losses compared with those generated when the diameter increased. Additionally, metal fasteners caused higher energy losses by up to 30% when fixed on mortar, compared with the energy losses incurred when they were fixed on bricks

Evaluating the role of next-generation sequencing and radiological techniques in rare disease diagnosis: Challenges and opportunities

Aim: This article evaluates the utility of next-generation sequencing (NGS) and radiological techniques in the diagnosis of rare diseases, emphasizing the challenges and opportunities presented by these technologies. Methods: A comprehensive review of existing literature on NGS technologies, including first, second, and third-generation sequencing methods, as well as their applications in genomics, transcriptomics, and epigenomics, was conducted alongside radiological imaging techniques such as MRI and CT scans. Results: NGS has revolutionized rare disease diagnosis by enabling high-throughput, cost-effective sequencing, facilitating the identification of pathogenic mutations, and advancing personalized medicine. Radiological techniques provide complementary insights into anatomical abnormalities and disease progression. Despite significant advantages, challenges such as data interpretation, cost, and ethical considerations persist. Conclusion: NGS and radiological imaging offer transformative potential in rare disease diagnosis, enhancing our understanding of genetic and anatomical aspects of disorders and enabling targeted therapeutic approaches. Continued technological advancements and integrative analyses with other omics data and imaging findings will further enhance their diagnostic utility