Engineering simulation and modelling has been adopted across a range of industry sectors due to its ability to reduce cost and time spent during product development as well as enhancing the safe operating life of components through the simulation of in-service conditions through a virtual representation or model of a real-world system. This virtual representation allows tests to be run virtually so behaviour can be observed over time under different conditions.
Removing the costs associated with physical prototypes and real-world testing, process modelling and simulations assist in decision-making by offering an insight into how systems will perform in different scenarios.
Our experts have been trusted by many of the largest and best-known names in industry to assist and advise on process modelling and simulation as well as undertaking projects for the direct benefit of our Industrial Member companies.
Core Research Programme (CRP)
The core research programme (CRP) involves the creation of projects to address challenges faced by our Industrial Members, advancing technologies and processes and finding new solutions for industry problems. These projects are jointly funded by our Industrial Members, with the outcomes made available to all of our Members.
- Fracture under Biaxial Loading using Finite Element Method
This 1996 project sought to use non-linear finite element analysis techniques to predict the effect of biaxial loading on fracture behaviour, where most fracture toughness test methods and assessment procedures assumed uniaxial loading. This included the assessment of a series of biaxial wide plate fracture tests that had been previously carried out on surface cracked and centre cracked panels that showed the varying effects of biaxial loads.
- Intermetallic Formation in Superduplex Steel Simulated HAZs
This 1997 CRP project investigated grades of 25%Cr superduplex stainless steels to determine whether the time to form intermetallic phases during isothermal heat treatment was similar to that during simulated weld thermal cycles. In addition, our research teams worked to determine whether intermetallic phases seen in real multipass welds can be induced by thermal simulation.
- Model for Predicting Cleavage and Ductile Fracture in Steel
Notched bend specimens had been shown to provide lower bound results for fracture toughness, ensuring conservative structural integrity assessments. However, the apparent fracture toughness of defects in structures which impose low levels of plastic constraint on a defect, for example shallow cracks or embedded defects in tensile stress fields, can be much higher than the recommended values measured on highly constrained test specimens. This can lead to unduly pessimistic assessments of defective structures that are actually fit for service. In addition, scatter in fracture toughness of ferritic steel and weld metals in the ductile-to-brittle transition region meant that statistical consideration was needed to provide a reliable lower bound estimate of fracture toughness. To address this, TWI developed micromechanical models to predict the stable growth of a flaw by ductile tearing or failure by cleavage fracture.
- Finite Element Analysis of Guided Waves in Pipe/Rail Flaws
This 2003 project aimed to validate a wave propagation modelling technique against experimentally measured transmission data in steel plate. This was undertaken to quantify the reflection characteristics of guided waves in both pipes and rails. In addition, the TWI team quantified the reflectivity of guided waves from flaws in rails.
- The Model Approach - Material Flow in FSW
Another 2003 process modelling and simulation CRP project investigated friction stir welding (FSW) in the light of several process advancements since it was first invented at TWI in 1991. These advancements created a need for an improved understanding of the process, such as with the amount of heat generated during the process and how material is swept past the tool during welding. Computer modelling had already allowed for an improved understanding of other aspects of FSW and so it was hoped that, by modelling material movement, the outcomes could inform factors such as tool design, parameter optimisation, and the investigation of difficult to weld materials.
- Cohesive Zone Modelling of Ductile Crack Growth in Steel
This project addressed the need for an improved methodology for the analysis of dynamic ductile crack propagation and arrest in high strength pipeline steels. This project opened with a review of the current approaches for selecting materials to avoid or arrest large ductile fractures, before the cohesive zone model of fracture was examined as a potential means to predict both stable and unstable ductile crack growth and arrest in fracture mechanics specimens and components. Test specimens were analysed, a finite element analysis model was implemented, and a test proposed to determine the parameters of the cohesive zone model.
- Weibull Model Manufacture of Ceramic/Metal Joints
Greater efficiencies can be gained in applications that require high temperatures (such as gas turbines, aero / automotive engines, and chemical plants) by increasing the temperature. However, at the time of this 2006 project, the maximum process temperatures of metal alloys were limited to about 700°C. Ceramic materials offered satisfactory properties above this temperature, provided they do not experience excessive tensile stress, since they have relatively low fracture resistance. It was believed that increased process efficiencies could be obtained using components with ceramic materials (where the temperature is high and applied stress is low) joined to metallic materials (where the temperature is lower and the stress is higher). Although brazing at high temperatures can join metal and ceramic materials, coefficients of thermal expansion cause high residual stresses to be generated during the cooling stage of the brazing cycle. The very high stresses, which increase as braze thickness decreases and build up at the edge of the joint, may cause the ceramic to fracture. The probability of fracture was known to increase the larger the size of the bonded surface is, however, conventional stress analysis of the manufacture of joints did not show a clear correlation between the observed failure and the predicted stress. This project sought to examine the feasibility of applying a finite element analysis and a Weibull failure model to determine the probability of failure in ceramic/metal joints. The work measured stresses produced during a brazing manufacturing cycle of ceramic/metal joints in a simple cross section, comparing experimental manufactured joints to predicted results.
- Low Stress No Distortion Aluminium Weld Modelling
A major cause of distortion in welded fabrications is material contraction as it cools and solidifies at different rates following the non-uniform heating produced by welding. Thinner materials are more prone to this distortion because they have less stiffness against out of plane bending as well as a lower resistance to bucking than thicker parts. This distortion particularly impacts industry sectors like automotive, aerospace, shipbuilding and space, where thin sheets and plates are widely used. Low stress no distortion (LSND) techniques can help reduce the plastic strain caused by contraction and phase transformations in and around the weld, thereby reducing the tendency for buckling and out of plane distortion in V prep butt welds. This 2008 project examined an auxiliary cooling LSND technique where atomised water is sprayed on the weld area through a nozzle trailing the welding arc. To use the technique effectively there was a need to determine the LSND parameters that minimise distortion in aluminium alloy plate, extending past CRP work in LSND joining of steel plates. The aim of this project was to simulate LSND welding of an aluminium alloy butt joint using a FE model to predict parameters optimised to minimise distortion. This would allow for the development of software to simplify the process of setting up a weld model.
- Sizing Locally Thinned Areas and Guided Wave Pipe Inspection
Guided waves had been used for the non-destructive testing of engineering structures for decades, but at the time of this 2008 CRP project there were still some challenges with the technique. Although it had proven valuable as a method for screening long, straight structures, such as pipelines, inspecting beyond features such as bends was still problematic since the waves are distorted as they propagate around the bend, causing mode conversions. Quantifying these effects would allow the bend to be accounted during testing. In addition, the guided wave signals was unable to distinguish between uniform circumferential thinning and a severe patch of localised corrosion at one circumferential position. This meant that when corrosion was detected, a pipe usually had to be excavated and replaced, regardless of whether this was actually necessary in reality. This project aimed to both quantify the effects of pipe bends on guided waves and find a technique for sizing locally thinned area defects in straight pipes using guided waves. The work undertaken in this project was expanded upon and continued in a follow-up, 2009 CRP project investigating long-range guided wave inspection beyond pipe bends.
- Modelling and Validation of Direct Metal Laser Deposition
This 2009 CRP project sought to model direct metal laser deposition (DMLD), a well-known additive manufacturing technique. The aim was to link the process parameters used with the microstructure that is created and the properties of particular metal deposits using a multiphysics solution. The project developed numerical models using commercially available software tools, providing a deeper understanding of the processes involved and providing recommendations for further work.
- Residual Stresses in Steel Girth and Butt Welds
This project addressed the topic of residual stresses and their measurement through the plate thickness as well as on plate surfaces so as to provide realistic values for use in engineering critical assessments (ECAs). This helped reduce the conservatism that arose from an assumption of a residual stress of yield strength. It was also important to quantify the effects of various parameters on residual stress distribution (e.g. geometric variations, external loading and crack growth) so that appropriate considerations of welding residual stress could be given to corresponding conditions in ECAs.
- Advances in Computer Based Prediction of Weld Distortion
Welding distortion occurs as a result of non-uniform thermal expansion and contraction of the weld and surrounding base material caused by the heating and cooling cycle of welding or cutting processes. Tensile stresses around the weld and compressive stresses across the rest of the plate can lead to distortion. Quantifying this distortion moved from a physical experimental experience to the construction of prototypes with cost-effective real-time virtual welding technology where efficient distortion modelling is key. We conducted a literature review of welding distortion simulation approaches with a focus on large, welded structures with the aim of being able to select the most appropriate approaches in welding distortion modelling for practical use.
- Measurement/Modelling R-Curves for Low Constraint Specimens
R-curves, or tearing resistance curves, represent how well a material can resist progressive crack extension. However, it can take the testing of several specimens to determine a single J-R curve, creating a high labour and material cost. An alternative is to undertake a single specimen test with only the initial and final crack lengths and the load-displacement curve being required. R-curve generation through modelling began to be assessed as a viable alternative, leading to this project to review R-curve testing methods and carry out fracture tests for low-constraint specimens, before deriving constraint-dependent R-curve using constraint parameters and developing a method for predicting J-R curves using cohesive zone modelling.
- Industrial Applications of Multi-Scale Modelling
Being able to understand material behaviour at scales below continuum mechanics can aid in the understanding of how engineering structures and processes will perform. Among the tools available for this are theoretical models formulating analytical expressions and computational calculations of representative volume elements (RVE). As industry sought modelling techniques to simulate materials behaviour across a range of scale lengths, TWI undertook this project to identify the benefits and limitations of using multi-scale methodologies based on micro-mechanisms at a local scale and the use of the fundamental behaviour to determine information about the macro scale.
- PZFlex Ultrasonic Beam Profile/Response on Fatigue Cracks
This 2011 project investigated the validation of the performance of finite element analysis (FEA) for modelling the inspection of small fatigue cracks using ultrasonic phased array techniques. Theoretical models for ultrasonic inspection have been developed over a number of years, where they are used to support the optimisation, the validation and a faster understanding of ultrasonic procedures without manufacturing of expensive mock-ups. This project worked upon the premise that FEA could provide a more accurate approach than alternative methods for the simulation of situations such as cracks without complex geometries, cracks grouped in clusters, and cracks that are small compared to the ultrasonic wavelength. The project focused on small smooth cracks as they were easier to model at this initial stage.
- Methods for Measurement and Prediction of Residual Stresses in Pipe Girth Welds in Clad Pipes
The level of welding residual stress is an important factor when undertaking an engineering critical assessment (ECA) of structures and components such as pipeline girth welds. Because of this, there have been a large number of experimental and numerical studies into through-wall distributions of residual stresses at pipe girth welds. The studies resulted in the generation of residual stress profiles recommended in fitness-for-purpose procedures such as BS 7910 (BSI, 2007), R6 (EDF, 2011) and API 579-1/ASME FFS-1 (API, 2007). However, none of these profiles related to the residual stresses in clad pipes in which the girth weld is made using a corrosion resistant (CRA) consumable, leading to a dissimilar metal joint. Hence this project carried out an investigation into the welding residual stresses in clad pipe girth welds in order to provide information for the ECA of clad pipe girth welds.
- Long-Range Guided Wave Pipe Modelling and Inspection
Although guided wave inspection can provide full volumetric coverage of tens of metres of pipe from a single test location it can be complex with factors such as vibrational modes, dispersion and multiple reflections to consider. The technique had been highlighted as a potential solution for unpiggable sections of pipeline, but this would often mean the need to account for bends in the pipe that distort the received signal. This project addressed this issue by using a combination of finite element analysis and experimentation to understand the behaviour of guided waves in a relatively tight pipe bend, building upon past research carried out at TWI to develop a technique to correct signal distortion caused by propagation around a bend.
- FEA Response Probabilistic Assessment of Pipeline Flaws
By the time of this project in 2012, deterministic analysis of the integrity of pipes containing flaws was week established. However, there was a requirement for a full probabilistic fracture mechanics analysis using the finite element method for more accurate prediction of the probability of failure of flawed structures. Most probabilistic models focused on fracture of structures under elastic or small plastic deformation, but probabilistic analysis for large plastic deformation and strain-based design for pipelines had received only very limited attention. This project worked to develop a framework for investigation of the probability of failure of structures containing flaws subjected to large plastic deformation via numerical modelling.
- Validation of Process Models for Additive Manufacturing
This CRP project was conducted in collaboration with the SIMULIA brand of Dassault Systèmes to validate finite element modelling (FEM) techniques capable of accurately simulating additive manufacturing (AM) processes, allowing improved part design and process setup before any physical manufacturing takes place. The project began with the production of double cantilever parts (Figure 1) using a Renishaw AM250 machine. All parts were produced using Ti-6Al-4V Grade 23 metal powder with a powder particle size range between 15 and 45μm. A 90° alternating scan strategy was used, comprising a series of parallel hatch lines and four boundary contours, rotated by 90° every layer. After manufacturing the double cantilevers, wire electrical discharge machining was used to cut the support structures just below the solid beam surfaces. Upon cutting, the presence of residual stresses generated deflections of the remaining double-sided cantilever beam structure. The out-of-plane deflections were measured using a FaroArm precision measuring tool. Once this was complete, a simulation model was employed, including temperature-dependent material properties for the heat transfer and stress analysis simulations. An image of the residual stresses after the wire cutting is shown in Figure 2. The measured deflections from the test pieces were then compared with the FEM predictions (Figure 3), showing strong agreement between the predictions and measurements, leading to confidence in the use of this new modelling approach.
- Fatigue Reassessment of Ageing Pressure Vessels
Modelling played a role in this 2017 project that sought to solve a problem related to the life extension of ageing pressure vessels that had been designed with a notional 25-year design life. These vessels had been designed in accordance with standards like BS 1515, which did not require fatigue assessment, meaning that their fatigue lives had never been calculated. To support offshore operators with the life extension of vessels designed to these older codes, we undertook a campaign of risk-based inspection, detailed modelling and fatigue assessment to highlight five necessary phases for their reassessment.
- Finite Element Analysis of Selected Welded Wide Plate Tests
This project worked to reduce the conservatism inherent in the equations and formulae for engineering critical assessments in procedures such as R6 and BS 7910. Finite element analysis was used to reassess wide plate tests that had been assessed using R6 and BS 7910 to demonstrate how modelling can improve the accuracy of a fracture assessment.
- Robotic Arc Welding and AM Process Parameter Optimisation
Although multi-axis industrial robots were widely used for arc welding, providing increased productivity and improved quality for a range of sectors, there were still issues around the development of new products, which still used a trial-and-error experimental approach to determine welding parameters. To improve this, TWI launched a CRP project to use a numerical modelling approach to improve parameter development. The concept that was developed for robotic arc welding could be adapted for other robotic welding and material processing methods, representing an important part of intelligent automation for welding and additive manufacturing.
- Adhesive-Free Bond Strength Test Method for Cold Spray Coatings
As the market for the use of thermal spray coatings for the repair of high value components and mitigating corrosion grew, there was an increased need for accurately measuring the coating adhesion strength. Such measurements had been done using tensile adhesion tests, whereby a stud is attached to the coating surface using an adhesive before a controlled strain rate tensile test is performed until the coating fails. However, advances in thermal and cold spray technology resulted in some coating bond strengths exceeding 70MPa, the maximum strength of available adhesives, creating the need for a new approach to determine these higher coating bond strengths. During this project, an adhesive-free adhesion test was developed that allowed assessment of coatings with bond strengths beyond 90MPa. However, modelling showed that while the adhesive-free adhesion test allows measurements of coatings with significantly greater bond strength, this test underestimated the true adhesion strength which must be considered when reporting results.
- Treatment of Residual Stresses Considering Elastic Follow-Up
Residual stresses introduced to a cracked component during welding or installation can cause it to fail at a lower applied load than expected. Structural integrity assessment codes such as R6, BS 7910 or API 579 classify those stresses that contribute to plastic collapse of the structure as primary stresses and those that do not as secondary stresses. These codes typically treat residual stresses as secondary stresses, but it is noted that long range residual stresses are associated with significant “elastic follow-up,” which tends to increase the permanent plasticity at a localised region of an engineering component, and therefore may be classified as primary stresses. However, at the time of this project, there was no detailed guidance as to what level of elastic follow-up should be deemed to be significant and therefore whether welding residual stresses or long-range residual stresses should be seen as primary, secondary, or somewhere between the two. TWI applied theoretical models and finite element analysis (FEA) to quantify elastic follow-up in three-bar structure benchmark models containing fit-up residual stresses and a plate model containing welding residual stresses. The benchmark models were studied for the effects of elastic follow-up on crack driving force, plastic collapse and residual stress relaxation via finite element analysis, before the finite element modelling of a plate containing welding residual stresses that had been introduced into the plate using a mapping technique. The influence of elastic follow-up on the redistribution of welding residual stresses was examined and the implications of residual stress treatment in the context of fracture assessment were explored, helping provide additional guidance for our Industrial Members.
- TITAN: Thermoacoustic Innovative Technology
Completed in 2023, TITAN was an Innovate UK feasibility project to investigate the potential application of a thermoacoustic generator (TAG) device to harvest waste energy from marine vessel engines (Figure 4). Working alongside European Thermodynamics Ltd and the University of Leeds, TWI helped design and manufacture a prototype device to maximise waste heat capture efficiency in small, economic, and modularised thermoacoustic Stirling engine recuperators. The aim was to harvest the thermal fuel energy lost through exhaust systems so it can be converted into pressure waves via thermoacoustics and generate electricity. TWI supported the TITAN project with multiple finite element (FE) models to analyse the thermo-mechanical stresses of the hot heat exchanger (component with highest risk) in order to inform component design and integrity. Our experts also advised on optimum joining methodologies for joints within the TAG, to ensure joint integrity.
- Development of Advanced Material Model for Metal Additive Manufacturing
Despite advances in additive manufacturing technologies by the time of this 2023 CRP project, wide scale industry adoption was still hampered by the structural integrity and reliability of additively manufactured metallic parts. This was primarily due to the difficulties in robustly correlating the link between processing conditions, manufacturing defects, material structure, and mechanical performance. Experimental trials were difficult, time consuming and costly because of the large number of variables to consider, so TWI explored a numerical modelling approach to address the problem. Specifically, we developed, implemented and validated a thermo-mechanical-metallurgical manufacturing process simulation for the powder bed fusion - laser beam (LBF-LB) processing of Ti-6Al-4V and other common AM alloys (Figure 5). This CRP project furthered the work of a previous Innovate UK (IUK) collaborative project called DREAM (Distortion Reduction and Elimination for Additive Manufacturing), which brought together real-time data acquisition, advanced modelling, cloud-based computing, and adaptive machine process parameter controls to achieve zero-distortion LPBF additive manufactured builds (Figure 6). Between them, these projects established the value of modelling and simulation to support the development of AM technologies.
- Evaluation of Resistance to Hydrogen Embrittlement of Dissimilar Metal Welds using Fracture Mechanics Principles and Coupled Mechanical-hydrogen Numerical Models
Despite widespread use across areas such as chemical processing, energy and subsea applications, the performance of dissimilar metal welds (DMWs) between low alloy steels and corrosion-resistant alloys in hydrogen-charging conditions were difficult to predict. The significant risk of hydrogen embrittlement (HE) in DMWs led to unknown levels of conservatism due to a lack of standardised testing guidelines, despite the use of qualitative fracture mechanics-based ranking tests. To increase the use of DMWs in design and fitness-for-service assessments, we conducted a study that employed a combined experimental and modelling approach to investigate HE in DMWs. Single edge notched bend and tension (SENB and SENT) fracture toughness tests were conducted under cathodic polarisation in a sodium chloride solution across a temperature range of 4 to 80°C to evaluate the temperature effect on environmental fracture resistance. At the same time, coupled hydrogen diffusion-mechanical numerical models were developed to demonstrate the differences in apparent toughness in terms of hydrogen diffusion towards highly strained regions of the DMW joint. The testing programme and models developed throughout this project revealed a complex relationship between the strains generated during fracture toughness testing and hydrogen diffusion to the fracture process zone, influenced by temperature and constraint. The numerical models developed during this project offered potential for identifying the most suitable type and amount of tests to perform based on the conditions and loading scenarios that in-field components are likely to encounter. Furthermore, the same experimental and modelling approach could be applied to simulate the behaviour of in-service components operating under hydrogen-charging conditions, thereby assessing whether such components are at increased risk of hydrogen embrittlement in the field.