M. Amir Siddiq

• Dr.-Ing
• Reader in Solid Mechanics and Materials at University of Aberdeen

Residual stress induced during and as a result of manufacturing processes can have a significant impact on the later stages of manufacturing (e.g., machining), and in-service performance (e.g., resistance to fatigue) of a component. In this work, a novel approach is presented by combining FE based residual stress predictions with experimental verif...

This study investigates the influence of ambient conditions on cryogenic cooling times for medium-carbon steel-grade ISO EN 1.0456 (ASTM A333 Gr.6) processing pipes, focusing on the air velocity, ambient temperature, and cooling medium. Using MATLAB, baseline cooling times were computed for air velocities of 0–25 m s⁻¹, considering both in-air cool...

This paper presents a feasibility study of the Cryogenic Cooling and Cutting System (CCCS), an embrittlement-based technique for offshore wind monopile foundations. The CCCS employs cryogenic treatment of the monopile wall surface to significantly reduce its impact energy absorption capability significantly, aiming to achieve shorter overall cuttin...

Metastable β titanium alloys are widely applied in many industries. These alloys can have plastic deformation via dislocation slip, twinning, stress-induced martensite (SIM), or a combination of these. These alloys fail in a ductile manner via a process of void nucleation, growth, and coalescence. Inherent defects, such as voids, are commonly attri...

This study delves into the significant area of low-energy impact fracturing within ISO EN 1.0577 (S355J2) mild carbon steel grade, exploring its cooling time depending on diverse temperature gradients across varying wall thicknesses. The cooling behavior is analyzed systematically to comprehend the material's structural dynamics under different the...

This study investigates the influence of ambient conditions on cryogenic cooling times for low-carbon steel-grade ISO EN 1.0456 (ASTM A333 Gr.6) processing pipes, focusing on air velocity, ambient temperature, and cooling medium. Utilising MATLAB, baseline cooling times were computed across air velocities ranging from 0 to 25 m/s, encompassing in-a...

Due to attractive mechanical properties, metastable β titanium alloys have become very popular in many industries including aerospace, marine, biomedical, and many more. It is often the complex interplay among the different deformation mechanisms that produces many of the sought-after properties, such as enhanced ductility, super-elasticity, and sh...

This paper presents a feasibility study of the Cryogenic Cooling and Cutting System (CCCS), an embrittlement-based technique for offshore wind monopile foundations. The CCCS employs cryogenic treatment of the monopile wall surface to significantly reduce its impact energy absorption capability significantly, aiming to achieve shorter overall cuttin...

When structures are commissioned, they deteriorate with time. The time to failure of a structure is a function of the mode and rate of overall deterioration of the structure. Considering all the deterioration mechanisms and failure modes possible for detailed analysis is a complicated and inefficient endeavour. Hence, it is useful to streamline eff...

We have investigated the influences of high-frequency vibration (HFV) superimposed onto the monotonic uniaxial tension in single-crystal aluminum (Al) specimens by molecular dynamics simulations. It was found that HFV induces softening, i.e., reduction in peak stress. Similar to previous experimental results, the softening increases with the increa...

Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals. α–β titanium alloys are ductile in nature and are widely used for their unique set of properties such as specific strength, fracture toughness, corrosion resistance and resistance to...

The latest advances in optimising the process parameters of laser powder bed fusion (LPBF) result in high densification part. Nonetheless, slight variations of those parameters or the use of recycled powder leads to sub-optimal parts, containing more defects. AlSi10Mg samples were produced by LPBF using recycled powder to study the effect of proces...

Austenitic stainless steels are used for a variety of applications and could suffer degradation of properties when exposed to hydrogen. The performance of these steels are also dependent on crystallographic texture which in practice is a factor influenced by manufacturing processes. A study has been performed using a crystal plasticity based finite...

This short paper presents the potential of using machine learning to predict materials behaviour in the context of hydrogen interaction with steel. Effort has been made to understand the quality, and amount of data needed to get improved predictions. An approach known as physics informed machine learning has been adapted in a simplified way through...

A study has been performed using a crystal plasticity based finite element method to understand the effect of various stress states and crystal orientations with respect to loading direction for FCC single crystals in both hydrogenated and nonhydrogenated environment. Simulations have been performed for a variety of stress triaxilaities, Lode param...

A study has been performed using a crystal plasticity based finite element method to understand the effect of various stress states and crystal orientations with respect to loading direction for FCC single crystals in both hydrogenated and non-hydrogenated environment. Simulations have been performed for a variety of stress triaxilaities, Lode parm...

In this work, the mechanical behaviour and microstructure changes of AA-7075 alloy subjected to a repetitive-bending-under-tension (R-BUT) process were studied. In the R-BUT process, a metallic strip undergoes repeated localised bending and unbending. Load-displacement curves derived from R-BUT tested samples displayed a drastic increase in elongat...

A crystal plasticity-based finite element study is performed to understand hydrogen effects on void growth in single crystals of austenitic stainless steel. The model assumes plastic deformation is driven primarily by dislocation motion and captures the influence of hydrogen. Hydrogen effects are incorporated by assuming agreement with the hydrogen...

A data-driven finite element method that accounts for more than two material state variables has been presented in this work. Data-driven finite element method framework can account for multiple state variables, viz. stresses, strains, strain rates, failure stress, material degradation, and anisotropy which has not been used before. Data-driven fin...

The aim of this work was to study the cold formability of commercially pure Titanium alloy (Grade 2) by a testing methodology known as repetitive bending under tension (R-BUT). A dedicated test rig to perform the test was designed and fabricated to analyse the room temperature deformation behaviour of Ti-50A alloy sheet of 1.2 mm thickness. Samples...

A data driven computational model that accounts for more than two material states has been presented in this work. Presented model can account for multiple state variables, such as stresses, strains, strain rates and failure stress, as compared to previously reported models with two states. Model is used to perform deformation and failure simulatio...

A model has been developed which simulates the deformation of single crystal austenitic stainless steels and captures the effects of hydrogen on stress corrosion cracking. The model is based on the crystal plasticity theory which relates critical resolved shear stress to plastic strain and the strength of the crystal. We propose an analytical repre...

A data driven finite element method (DDFEM) that accounts for more than two material state variables has been presented in this work. DDFEM framework can account for multiple state variables, such as stresses, strains, strain rates, failure stress, material degradation, and anisotropy. DDFEM is implemented in the context of linear elements of a non...

Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals. {\alpha}/{\beta} titanium alloys are ductile in nature and are widely used for their unique set of properties like specific strength, fracture toughness, corrosion resistance and res...

Interesting stuff on the way...

A model has been developed which simulates the deformation of single crystal austenitic stainless steels and cap-tures the effects of hydrogen on stress corrosion cracking. The model is based on the crystal plasticity theory which relates critical resolved shear stress to plastic strain and the strength of the crystal. We propose an analytical repr...

The effect of hydrogen on the fracture behaviour of austenitic stainless steel has been investigated in the past [1][2]. It has been reported that fracture initiates by void formation at inclusions and regions of enhanced strain localisation [3]. There is experimental evidence that supports the fact that hydrogen influences void nucleation, growth...

Local mode mixity and stress triaxiality plays an important role during metal/ceramic interface fracture. It has been reported in the literature that the ratio of the fracture energies to the mode I fracture energy can vary from 1 to 5. For many of the bimaterial systems, the reason has been reported to be the local mode mixity and stress triaxiali...

Hydrogen enhanced cracking is one of the many failure mechanisms in metals depending on the corrosive environment. In the presented work, a multiscale constitutive model has been presented for hydrogen enhanced intergranular cracking in metals. The proposed constitutive model takes into account one of the many micromechanisms, i.e. Slip based micro...

A data driven computational model that accounts for more than two material states has been presented in this work. Presented model can account for multiple state variables, such as stresses, strains, strain rates and failure stress, as compared to previously reported models with two states. Model is used to perform deformation and failure simulatio...

High strength titanium alloys are generally used in widespread applications ranging over, but not limited to biomedical, aerospace, automotive, marine, oil and gas, and energy. Besides other manufacturing processes, forming is one of the common manufacturing processes used to produce components out of these alloys. Forming processes generally invol...

Crystal plasticity based finite element method (CPFEM) studies have been successfully used to model different material behaviour and phenomenon, including but not limited to; fatigue, creep and texture evolution. This capability can be extended to include the ductile damage and failure in the model. Ductile failure in metals is governed by void nuc...

This work presents a porous crystal plasticity model which incorporates the necessary mechanisms of deformation and failure in single crystalline porous materials. Such models can play a significant role in better understanding the behaviour of inherently porous materials which could be an artefact of manufacturing process viz. 3D metal printing. T...

Syntactic foams with hollow glass microspheres embedded in an epoxy matrix are used in marine, aerospace and ground transportation vehicle applications. This work presents an in situ experimental study of failure mechanisms in syntactic foam based on X-ray microcomputed tomography with uniaxial compression. Under different levels of compressive str...

High strength aluminium alloys that are produced through forming and joining processes are widely used in aerospace components. The ductile failure in these metals occurs due to the evolution and accumulation of microscopic defects, such as microvoids and shear bands. The present work investigates the underlying physical mechanisms during ductile f...

This paper presents the feasibility study of potential application of recently developed surface defect machining (SDM) method in the fabrication of silicon and similar hard and brittle materials using smooth particle hydrodynamics (SPH) simulation approach. Simulation study of inverse parametric analysis was carried out to determine the Drucker-Pr...

Aluminium alloys are typically used in a variety of applications, which require high strength, ductility and formability. In order to understand the formability of such alloys along with underlying mechanisms, a CPFEM based study has been performed using crystal plasticity theory. Crystal plasticity finite element methods [1]–[4] have been used to...

Incremental sheet forming (ISF) is an emerging manufacturing technique in which sheet metal is formed through application of localized force using a moving tool. ISF has many potential uses for manufacture of small batches and product prototypes in industries such as aerospace and automotive (where pressed sheets components are common). The advanta...

We present for the first time a numerical multiphysics peridynamic framework for the modelling of adsorbed-hydrogen stress-corrosion cracking (SCC), based on the adsorption-induced decohesion mechanism. The material is modelled at the microscopic scale using microstructural data. First-principle studies available in the literature are used for char...

In the presented work, an effort has been put to clear up the theoretical interlink between local adhesion capacity and macroscopic fracture energies by bridging different length scales, such as nano-, meso-, and macro-scale. Crystal plasticity theory along with a cohesive modelling approach has been used during this work. The influence of differen...

A variational multiscale constitutive model that accounts for strain rate dependent ductility of nanocrystalline materials during intergranular failure has been presented. The presented model is an extension of the previous work [1], in which a nanocrystalline material is modelled as two-phase with grain interior being modelled using crystal plasti...

The complex prototype forming of an industrial component was investigated on AA2024, 5083 and 7075 sheets using the incremental sheet forming approach. Fracture occurred at the top of crevice and steeper wall angle region for AA2024 and 7075, respectively, whereas no fracture in the AA5083 alloy. Thinning was higher at the steeper wall angle for al...

The complex prototype forming of an industrial component was investigated on AA2024, 5083 and 7075 sheets using the incremental sheet forming approach. Fracture occurred at the top of crevice and steeper wall angle region for AA2024 and 7075, respectively, whereas no fracture in the AA5083 alloy. Thinning was higher at the steeper wall angle for al...

Intergranular stress corrosion cracking (IGSCC) is a fracture mechanism in sensitised austenitic stainless steels exposed to critical environments where the intergranular cracks extends along the network of connected susceptible grain boundaries. A constitutive model is presented to estimate the maximum intergranular crack growth by taking into con...

We present a two-phase constitutive model for pseudoelastoplastic behavior of porous shape memory alloys (SMAs). The model consists of a dense SMA phase and a porous plasticity phase. The overall response of the porous SMA is obtained by a weighted average of responses of individual phases. Based on the chosen constitutive model parameters, the mod...

We present a micromechanics-based thermomechanical constitutive model to simulate the ultrasonic consolidation process. Model parameters are calibrated using an inverse modeling approach. A comparison of the simulated response and experimental results for uniaxial tests validate and verify the appropriateness of the proposed model. Moreover, simula...

We present a computational study of ultrasonic assisted manufacturing processes including sheet metal forming, upsetting, and wire drawing. A fully variational porous plasticity model is modified to include ultrasonic softening effects and then utilized to account for instantaneous softening when ultrasonic energy is applied during deformation. Mat...

In this work, a computational framework has been proposed to successfully simulate the fibre embedding using ultrasonic consolidation process. The main components of the proposed computational approach are a developed constitutive model and a friction model which are especially suitable for the condition of ultrasonic process. The effect of differe...

We present a variational void coalescence model that includes all the essential ingredients of failure in ductile porous metals. The model is an extension of the variational void growth model by Weinberg etal. (Comput Mech 37:142–152, 2006). The extended model contains all the deformation phases in ductile porous materials, i.e. elastic deformation...

In this paper, a phenomenological crystal plasticity model is modified to account for acoustic (ultrasonic) softening effects based on the level of ultrasonic intensity supplied to single and polycrystalline metals. The material parameters are identified using the inverse modeling approach by interfacing the crystal plasticity model with an optimiz...

Interface failure in metal/ceramic composites plays an important role in modern materials technology, as evident by their use in a variety of applications. High-strength materials, such as metal-matrix composites consist of internal interfaces between ceramic (e.g. SiC or Al2O3) particles or filaments within a metallic host. In microelectronics pac...

This work presents a computational framework based on finite element methods to simulate the fibre-embedding process using ultrasonic consolidation process. The computational approach comprises of a material model which takes into account thermal and acoustic softening effects and a friction model which indicates the realistic friction behaviour at...

Ultrasonic welding can be used to join plastic and metal through high-frequency (more than 20 kHz) acoustic vibrations. Aluminium alloy is widely used in electronics, automotive and aerospace. The mechanical vibrations used during ultrasonic metal welding are introduced horizontally. During ultrasonic metal welding, a complex process is triggered i...

The fiber push-out test is a basic method to probe the mechanical properties of the fiber/matrix interface of fiber-reinforced metal matrix composites. In order to estimate the interfacial properties, parameters should be calibrated using the measured load–displacement data and theoretical models. In the case of a soft matrix composite, the possibl...

Ultrasonic welding (consolidation) process is a rapid manufacturing process that is used to join thin layers of metal at low temperature and low energy consumption. Experimental results have shown that ultrasonic welding is a combination of both surface (friction) and volume (plasticity) softening effects. In the presented work, an attempt has been...

Ultrasonic welding process is a rapid manufacturing process used to weld thin layers of metal at low temperatures and low energy consumption. Experimental results have shown that ultrasonic welding is a combination of both surface (friction) and volume (plasticity) softening effects. In the presented work, a very first attempt has been made to simu...

In the presented work, an effort has been put to clear up the theoretical interlink between local adhesion capacity and macroscopic fracture energies by bridging different length scales, such as nano-, meso-, and macro-scale. Crystal plasticity theory along with a cohesive modelling approach has been used during this work. The influence of differen...

Ultrasonic consolidation process is a rapid manufacturing process used to join thin layers of metal at low temperatures and low energy consumption. In this work, finite element method has been used to simulate the ultrasonic consolidation of Aluminium alloys 6061 (AA-6061) and 3003 (AA-3003). A thermomechanical material model has been developed in...

Two continuum mechanical models of crystal plasticity theory namely, conventional crystal plasticity theory and mechanism-based crystal plasticity theory, are used to perform a comparative study of stresses that are reached at and ahead of the crack tip of a bicrystal niobium/alumina specimen. Finite element analyses are done for a stationary crack...

The present paper examines the crystal orientation effects on the energy at the crack-tip of nio-biumjalumina joints. The analyses have been done using crystal plasticity theory. The single crystal parameters are identified for each family of slips system in [21]. These identified parameters are being used to examine the orientation effects of the...

The present paper examines the crystal orientation effects on the energy at the crack-tip of niobium/alumina joints. The analyses have been done using crystal plasticity theory. The single crystal parameters are identified for each family of slips system in [21]. These identified parameters are being used to examine the orientation effects of the n...

The present paper examines the interface fracture of a bicrystal niobium/alumina specimen using a cohesive modelling approach. Crystal plasticity theory has been used to model the single crystalline niobium. The effect of different cohesive law parameters, such as cohesive strength and work of adhesion, has been studied. The cohesive strength is fo...

Metal/ceramic interfaces play a vital role in modern materials technology, as evident by their use in a variety of applications. High-strength materials, such as metal-matrix composites consist of internal interfaces between ceramic (e.g. SiC or Al2O3) particles or filaments within a metallic host. In microelectronics packaging, interfaces between...