Weld Geometry Research Articles

A simplified fracture mechanics method for fatigue life analysis of weld roots

Volvo CE currently uses the effective notch stress method for assessing fatigue life in welded structures. For large structures such as frames, a sub modelling technique with a very fine mesh is necessary using millions of DOF. Stress tensors from unit load cases, estimated with FEA, are combined with time history loading from Multi Body Simulations of the complete machine operating on customer representative digitized test tracks. A critical plane approach (the Modified Wöhler Curve Method) is used to estimate the fatigue life. The usage of the effective notch method implies a very time-consuming design process. An LEFM approach for weld roots would be even more time-consuming but would be a more natural approach since the weld root consists of crack like defects. To overcome the drawbacks with the current design process that involves usage of the effective notch method, a hybrid method is defined using pre-calculated geometry factors for different crack sizes and weld geometries. The geometry factors as a function of crack size, and the weld geometry, are stored in a database. From the unit load cases the structural stress using a coarse mesh in the weld is extracted. Together with the geometry factors, the stress intensity factors may be estimated and used with Paris law to calculate the fatigue life of welds. A comparison between the effective notch method, LEFM and the new hybrid method is carried out for typical fillet welds is presented in this paper.

Effect of measured local weld geometry and its variability on the local weld stress

The local weld geometry and its variability can significantly affect the fatigue strength of structures, especially for non-load-carrying welds. Standardised definitions, such as sharp transition radii or undercuts, govern stress-raising effects at the weld toe. High-resolution digital tools can nowadays accurately determine these parameters, allowing for studying the impact of geometry variability on fatigue strength. However, real welds rarely exhibit idealised transitions as multiple radii, undercuts, and ripple lines introduce uncertainty in geometry estimations. Numerical simulations of the actual weld geometry, with all its variations, in combination with probabilistic evaluations, have shown great potential for studying the influence of competing notches in the weld. This study compares probabilistic evaluations of 3D scanned welds with analytical relations for stress concentration factors. Results reveal no clear trend between the analytical expressions and the ratio of simulated sectional stress to nominal stress. This highlights the challenge of directly applying existing analytical equations to idealised measurement data from real welds in their as-welded condition for fatigue strength estimations.

Mathematical Modelling to Predict Bead Geometry Parameters of MIG Welded Aluminum 6063 Plates

The purpose of this research is to evaluate the effect of various operational parameters like voltage, weld speed, torch angle, nozzle to plate distance (NPD), and wire feed rate on bead geometry of welds on aluminum 6063 plates. This aluminum grade has a wide range of applications, from industrial to home. The bead geometry properties of a fusion weld are essential from a design standpoint because they affect the joint's mechanical strength and dependability throughout its usage. Bead width (BW), depth of penetration (DOP), and height of reinforcement (HOR) are all essential bead parameters, which need to be considered while commenting on bead geometry of a weld. An experiment series was performed with the statistical technique of design of experiments, using the central composite rotatable design (CCRD) method. This resulted in a mathematical model that correlated bead geometry parameters with various input parameters. RSM (Response Surface Methodology) is used for the graphical analysis of the results obtained. The suggested framework aims to optimize the input variables in order to attain the specified bead parameter values.

Life-cycle Cost assessment of Post Weld treatments: Effect of local weld geometries

The fatigue life of welded structures is dependent on the local geometry and imperfections of the welds. Therefore, optimizing the manufacturing processes to improve the local weld geometry and remove possible imperfections can considerably affect the fatigue life of the structure. Post-weld treatments such as burr grinding, and High Frequency Mechanical Impact (HFMI) treatment are commonly used techniques to extend the fatigue life of a weld by modifying the local weld toe geometry. However, employing additional manufacturing processes can have an adverse effect on the Life-cycle cost of a welded structure by increasing production costs. On the other hand, extending the fatigue life of a structure can result in lower maintenance and replacement costs. Therefore, a thorough yet predictive life-cycle cost assessment is required to assess the viability of such treatments and design economically efficient weld structures.This study assesses the life-cycle cost of welded joints. The fatigue life of the weld in this study is analyzed using the effective Notch Stress method (NS). Furthermore, the weld is post-treated with an automated HFMI treatment to prolong its fatigue life. Moreover, the effect of weld quality on the production cost is analyzed. The results show that every phase of the weld's life-cycle has a significant contribution to the life-cycle cost with the use-phase being the more dominant. The results also depict the impact of the changes in weld quality in the overall life-cycle cost.

Reinforcement learning as data-driven optimization technique for GMAW process

Welding optimization is a significant task that contributes to enhancing the final welding quality. However, the selection of an optimal combination of various process parameters poses different challenges. The welding geometry and quality are influenced differently by several process parameters, with some exhibiting opposite effects. Consequently, multiple experiments are typically required to obtain an optimal welding procedure specification (WPS), resulting in the waste of material and costs. To address this challenge, we developed a machine learning model that correlates the process parameters with the final bead geometry, utilizing experimental data. Additionally, we employed a reinforcement learning algorithm, namely stochastic policy optimization (SPO), with the aim to solve different optimization tasks. The first task is a setpoint‐based optimization problem that aims to find the process parameters that minimize the amount of deposited material while achieving the desired minimum level of penetration depth. The second task is an optimization problem without setpoint in which the agent aims to maximize the penetration depth and reduce the bead area. The proposed artificial intelligence-based method offers a viable means of reducing the number of experiments necessary to develop a WPS, consequently reducing costs and emissions. Notably, the proposed approach achieves better results with respect to other state-of-art metaheuristic data-driven optimization methods such as genetic algorithm. In particular, the setpoint‐based optimization problem is solved in 8 min and with a final mean percentage absolute error (MPAE) of 2.48% with respect to the 42 min and the final 3.42% of the genetic algorithm. The second optimization problem is also solved in less time, 30 s with respect to 6 min of GA, with a higher final reward of 5.8 from the proposed SPO algorithm with respect to the 3.6 obtained from GA.

MICROSTRUCTURE AND PROPERTIES OF LASER-WELDED BUTT JOINTS OF AlSi1MgMn ALUMINIUM ALLOY

The process of autogenous laser welding of butt joints of aluminium alloy AlSi1MgMn plates with thickness of 3.0 mm was investigated. The Yb:YAG disk laser was used in the study. The aim was to determine the influence of the basic parameters of laser welding on the joint quality, fusion zone geometry, microhardness distribution across the butt joint, structure and microstructure of fusion zone (FZ) and heat affected zone (HAZ) was studied and determined. The chemical composition of the base metal was determined by spark emission spectroscopy, while the phase constituents were determined by XRD analysis. Results of the study have shown that the geometry of welds is proper without excessive imperfections. No voids were found the FZ. However, weld face of the joints are slightly convex, while the roots are slightly concave. Microscopic observations showed no discontinuities in the fusion zone of the welds. A significant decrease in hardness in the FZ was observed. The hardness in the FZ of the test joints is approx. 67÷70 HV0.1. The fracture of the samples during tensile tests occurred in the FZ or at the boundary FZ/HAZ, and the tensile strength was ranged from 200MPa to 220MPa.

Investigation of Weld Geometry, Mechanical Properties, and Metallurgical observations of Activated Flux Tungsten Inert Gas (A-TIG) Welding on 304 Austenitic Stainless Steel

Investigation of Weld Geometry, Mechanical Properties, and Metallurgical observations of Activated Flux Tungsten Inert Gas (A-TIG) Welding on 304 Austenitic Stainless Steel

Effects of preheating on laser beam–welded NSSC 2120 lean duplex steel

AbstractDuplex stainless steels show sustainable alternative for the conventional austenitic grades, with higher strength, higher resistance against stress corrosion cracking, and lower purchase cost. Thus, duplex stainless steel gains more attention in construction, oil and gas, and chemical industries. Among duplex stainless steels, low nickel and low molybdenum alloyed lean duplex stainless steel are a cost-effective substitution of austenitic grades. However, keeping the balanced ferrite/austenite phase ratio in the weld metal can be challenging, mostly for autogenous and low heat input welding processes. In our research, a newly developed NSSC 2120 lean duplex stainless steel grade was welded autogenously by fiber laser welding process. Different welding parameters and preheating temperatures were used during the experiments. The welds were evaluated by microscopic and metallographic techniques, and also by electrochemical corrosion measurements. The welding parameters and the preheating temperature greatly influenced the weld shape and the austenite content in the weld metal. It was found that the focus point distance from the sheet surface had significant effect on the weld geometry. Changing the focus point distance to + 2 mm, the penetration depth increased from 4.96 to 5.53 mm, and increased the austenite content by 2.6%. Due to the preheating the welds became wider and shallower, e.g., from 4.96 to 4.08 mm penetration depth, while the cross-section are increased from 5.10 to 6.12 mm2 at the same sample. The preheating resulted in more intergranular austenite formation, which meant maximum 4% increase in the weld metal. The increasing austenite content resulted in increasing pitting corrosion resistance in 3.5% NaCl electrolyte, the highest increase was 90 mV.

A novel post-weld treatment using nanostructured metallic multilayer for superior fatigue strength

Welded joints exhibit fatigue failure potential from weld geometry and characteristics of the heat affected zone. In order to counteract fatigue, structures and components require larger thicknesses resulting in heavier designs exhausting the finite natural resources. We hereby introduce a novel post-weld treatment, which postpones or even prevents fatigue failure of the welded connection. A Cu/Ni nanostructured metallic multilayer (NMM) is applied via electrodeposition and a 300–600% increase in usable lifetime compared to the untreated weld is observed. A FAT class 190 with a slope of k = 6 is proposed for the design of NMM treated butt welds. Material mechanisms responsible for the fatigue strength increase are introduced herein. A case study shows that the design of offshore wind turbine support structures applying NMM post-weld treatment enables a lifetime extension as well as a 28% weight reduction compared to the structure without post-weld treatment.

Improvement of electrical and mechanical properties of laser welded lap joints via dimensional optimization

With the proliferation of electric drivetrains, the development and optimization of joining techniques for the fabrication of battery packs became a prime manufacturing topic. Decreasing the electrical resistance and increasing the mechanical strength of the welds at the individual cell level are of great importance not only for productivity and efficiency but also for safety and sustainability purposes. Lasers offer an advanced, highly automatable solution for battery cell joining. Usually, the optimization focuses on the laser parameters or the scanning speed. However, the most widespread battery welding geometry, the so-called lap geometry, allows alternative possibilities for joint property optimization. The novelty of our approach is that we focus on systematic experimental investigation of the effects of dimensional parameters and the layout of the weld pattern. Systematic experiments reveal that the shape and size of the weld area have substantial effect on the properties of the laser welded joint. Our results prove that a rather substantial gain can be achieved in both the electrical and mechanical properties when the weld consists of at least two parallel bead segments. We also show that it is beneficial by both means if the segments have the greatest individual length and placed apart at the maximum feasible distance. The orientation of the straight segments affects the mechanical and electrical behavior differently: strongest welds consist of weld segments oriented in parallel, while the smallest resistance can be achieved using segments oriented perpendicular to the direction of current flow, respectively.

Influence of modelling methods of a fluctuating weld geometry on the fatigue assessment using the effective notch stress approach

Influence of modelling methods of a fluctuating weld geometry on the fatigue assessment using the effective notch stress approach

Dynamic ideality for electron beam welding

Experimental methods for evaluating performance of electron beams are both time consuming and costly, with favourable parameters chosen based on a subjective standard. Correlation of the weld geometry against conventional machine input parameters such as voltage, focus, and current involves complex interaction phenomena. This renders it difficult to deconvolute the influence of these inputs against applied energy distributions within a setup. In this work, a process window was generated across a range of weld powers and speeds with focal positions adjusted to achieve the same nominal spot size and hence mitigate input parameter interaction phenomena. The variability of spot size using this method can be reduced by 90% against using the conventional method of optically acquiring weld focus. To reduce reliance on empirically derived heuristics in parameter selection, weld performance was quantified through an aggregated output quality termed ‘ideality’ as a function of conventional weld geometry, imperfections, and characteristic microstructural evolution/transformation. The ideality metric was shown as a method of achieving the least harmful compromise of parameter conflicts. A method of using a thermal process model to perform subsequent optimisation of ideality was presented. The ability to characterise inputs as a function of beam properties rather than machine inputs serves as a useful method to optimise weld procedures and serve as a basis for comparison between setups. While electron beam welding is used in this study to propose ideality, process outputs and inputs can be substituted for other process-specific outputs and inputs, enabling adoption for most manufacturing processes.

Numerical design calculation of the high-strength steel welds

This study focused on the design of fillet welds fabricated using high-strength steel (HSS). Herein, we present a numerical design calculation (NDC) method for assessing weld strength using the regular inclined shell element model (RISEM) in the finite element method (FEM). The NDC uses the FEM to design joints according to standardised procedures. The inclined shell element in the RISEM represents the geometry and stiffness of the welds, which controls the stresses in the plane. We recommend using a common inclined shell element with rigid links to accurately represent the geometry and rigidity of fillet welds. A new strength criterion is proposed based on the stresses on the inclined shell element, using the maximum equivalent stress as an indicator. An experiment was conducted on the transverse fillet lap-welded connection from the S700 MC Plus steel plate and OK AristoRod 13.12 electrode at room temperature. The deformation capacity of the welded connection was measured via a non-contact process using the digital image correlation (DIC) technique. This method was validated by comparing the RISEM and test results using finite element (FE) simulations. Additionally, the weld resistance computed from the analytical model of prEN 1993–1–8:2020 was in good agreement.

Effect of Weld Geometry on Irradiation-Induced Segregation Resistance of 316L Stainless Steel Weld at 400 °C

Effect of Weld Geometry on Irradiation-Induced Segregation Resistance of 316L Stainless Steel Weld at 400 °C

Application of local fatigue approaches on corroded welded joints with consideration of weld geometry and residual stresses

Corrosion can significantly affect the fatigue strength of steel structures. On the one hand, it can cause stress concentrations by changing the surface geometry, and on the other hand, it can lead to embrittlement of the material. In welded steel components, sharp notches are already present due to the weld geometry, which may interact with the notches from corrosion. In addition, residual stresses exist in the fatigue-relevant area, which can also be partially modified by surface preparation methods such as clean blasting. In the current standards, all the mentioned effects are considered by reducing the design stress-life (SN) curves, in which all aforementioned effects are superimposed. One possibility to consider the effects separately is the application of local concepts, with which the influence of the geometry, here obtained from 3D-scans, the influence of measured residual stresses, and the influence of material can be considered individually. For butt and fillet welds investigated in this study, it could be shown that by considering the real geometry via a reverse engineered 3D-solid model, the locations of crack initiation in the fatigue tests, measured by digital image correlation (DIC), matched with the numerically predicted locations in most cases. Moreover, it was shown that by taking into account the real geometry and residual stresses, the use of local approaches can result in a substantially reduction of the scatter in SN-curves from Tσ = 2.17 to Tσ = 1.26, demonstrating the great reliability of the applied method.

Overload and variable amplitude load effects on the fatigue strength of welded joints

Different load spectra and individual load peaks might substantially relax high residual stresses as well as induce compressive residual stresses in welded components and, consequently, affect the fatigue performance of these joints. Consideration of peak loads and resulting relaxation of residual stresses in fatigue analyses can substantially enhance the accuracy of life prediction. The aim of the current study is to experimentally investigate the fatigue strength of welded joints subjected to different levels of overloads and variable amplitude (VA) loads and to develop local fatigue assessment method to account for the relaxation of residual stresses via a mean stress correction using the 4R method. The 4R method applies a local stress ratio for the mean stress correction considering material strength, residual stresses, applied stress ratio of external loading and local weld geometry in elastic–plastic material behaviour. Fatigue tests were carried out on fillet-welded longitudinal gusset joints made of S700 high-strength steels under applied stress ratio R = 0–0.1. A mild strength steel (S355) and ultra-high-strength steel (S1100) were selected as reference steel grades for the fatigue testing to study the material strength effects. Numerical analyses were conducted to evaluate the fatigue notch factors using the effective notch stress concept with the reference radius of rref = 1.0 mm and theory of critical distance (TCD) using the point method. The experimental results indicated that a substantial improvement in the fatigue strength capacity can be claimed in the joints subjected to tensile overloads, particularly in the studied S700 and S1100 steels. The higher-level overload (0.8fy), corresponding to the nominal cross-sectional area, improved the mean fatigue strength of the welded joints manufactured of high-strength S700 steel by approximately 60%, while the lower overload (0.6fy) improved the mean fatigue strength by 20%. In addition, a use of equivalent nominal stresses for the joints subjected to VA loads resulted in conservative assessments when employing S–N curves obtained for the CA loading. The 4R method, via the local mean stress correction for individual cycles, provided higher accuracy for the fatigue assessments.

The effect of weld bead heat input on the performance of thick 3CR12 stainless steel welds

3CR12 is a low cost special stainless steel containing 12% chromium. It is widely used in material handling, road transport, rail transport, power generation and petrochemical applications due to its favorable corrosion performance. 3CR12 is a weldable material, but it has challenges such as poor ductility, poor toughness of 3CR12 stainless steel welds, unfavorable microstructure and cross-sectional properties of the weld bead. This is due to the welding heat input and heat transfer across beads, which causes cracking due to property changes. When welding a thick stainless steel section, the hardest heat affected zone (HAZ) is created due to uneven heating and cooling in the weld metal and base material, which is susceptible to cold cracks and residual stresses, resulting in welding defects and unfavorable material properties. Welding thick 3CR12 stainless steels can be accomplished by using a variety of welding techniques. In order to restore undesirable material qualities, the majority of welds require a post-weld heat treatment (PWHT). However, critical PWHT factors such as duration, weld geometry, and unsupported loads during the hot phase of the weld do not always allow the process to be effective. This process results in prolonged downtime since the holding time in the PWHT cycle can be very long, especially with thick-walled 3CR12 steel members. There are other methods that are currently used to weld or repair thick 3CR12 steels. Among these other methods, the use of controlled temper bead welding technique which potentially could mitigate the above mentioned problems is mentioned. The approach involves using the heat input of the weld bead as a way of introducing the heat into the previous weld bead. This is achieved by varying the heat input in order to improve the mechanical performance of the previous weld bead and thus the overall weld integrity. Welding procedures for 3CR12 recommend the use of minimum heat to avoid weld defects and unfavorable material properties. This study was carried out to investigate the effect of the heat input of the weld bead on the mechanical properties of thick welds made of 3CR12 stainless steel. By utilizing inert gas (MIG) welding, two heat input levels were used in the process: low heat input averaged at 1.53 kJ/mm and high heat input averaged at 2.1kJ/mm. The heat input was varied by changing the welding parameters, for example the average welding voltage ranging from 28V to 30V, the average welding current from 120 A to 150 A and the average feed rate between 1.77mm/sec to 2.0mm/sec.

Integrated Assessment of MIG Welding Parameters on Carbon Steel using RSM Optimisation

This study examined how parameter optimisation in MIG welding affects material properties, weld quality, flexural strength, and weld bead geometry using an experimental design. Structural testing reveals that weld pool imperfections, especially in welded joints, often lead to metal failure. Incorrect selection of welding parameters, material weldability, and metal forming contribute to defects and necessitate post-treatment. The study aims to minimize weld defects and maximize material strength in welded parts using a quadratic second-order regression model to predict optimal process parameters. The chosen JIS G3131 hot-rolled carbon steel material is commonly used in automotive parts, is cost-effective, and can be easily welded. The welding process is MIG buttweld according to AWS 1.1 standards. The tests match the RSM design's 3-by-3 orthogonal array. The process parameters are welding current, arc voltage, and welding speed. The responses are bead height, bead width, penetration, and flexural strength. NDT X-ray radiography detects flaws in weld pools. The welded connection's durability is determined with a three-point bending test. Experiments are conducted to find the best input parameters with 95% confidence. This study also uses an experimental design based on an orthogonal array and an analysis of variance (ANOVA). Contribution to factors and regression analysis. The predicted flexural strength was 903.1 MPa, with a 0.66% error compared to the experimental value of 897 MPa. Predicted values for weld penetration, bead width, and bead height are 3.01, 9.45, and 2.04. In the RT inspection test, the test sample with the optimum parameters had no defects in the welded joint. The optimal parameter values for the regression analysis of the RSM combination are 115, 20, and 18 for current, speed, and voltage. Confirmation tests for DT and NDT were performed to validate the optimal parameter settings. This research shows that optimizing process parameters for welded products improves weld geometry and flexural strength. This method is widely used and valuable in metal fabrication.

Pulsed gas metal arc additive manufacturing of low-carbon steel: Microstructure observations and mechanical properties

Gas metal arc additive manufacturing (GMA-AM), also known as wire arc additive manufacturing (WAAM), uses an electric arc to melt a wire electrode and deposit objects layer by layer. This study focuses on creating single-pass wall structures using a low-carbon steel wire (ER70S-6) and examining the relationship between pulse frequency and weld geometry, microstructure, and mechanical properties. Microscopic observations showed a typical columnar microstructure with three distinct regions: acicular ferrite, bainite, and allotriomorphic ferrite in the first and last layers, while the mid-region exhibited homogenous polygonal ferrite grains with some pearlite at the grain boundaries. The tensile test results demonstrated a dependency of strength on the applied pulse frequency, with the highest strength (i.e., the ultimate tensile strength of 522 MPa and yield strength of 375 MPa with ductility of ∼52%) achieved in parts processed at a frequency of 100 Hz. Vickers microhardness values revealed uniform hardness in the middle region, consistent with the microstructure observation. Analyzing thermal cycles, coupled with microstructure analysis and continuous cooling transition diagrams, provided insight into how phase and microstructure evolution occurred in low-carbon low-alloy steels processed through PGMA-AM.

Analysis and design of column splicing flange joints with different weld types

To improve the seismic performance of steel column splicing flange joints, different weld details between the column and the flange plate were proposed in this study, and four full-scale specimens were designed and tested under cyclic loads. Finite element analysis was conducted to further check the joint performances and the weld behaviors. The hysteresis behaviors, yield moment, ductility, bolt forces, energy dissipation, stress and strains were analyzed. The parametric analysis, with finite element models validated by test results, was conducted, discussing the influences of the weld details, weld geometries and flange openings. According to the results, three of the four different weld details developed different advantages on ductility or energy dissipation capacity, bolt tension distribution, stress or strain distributions. Larger weld leg size would increase the resistance of the bolted flange splice joint, but may also cause weld residual stress and prying force. The reduction of flange opening can improve the stiffness and yield moments of the Type B flange joints. Formulas for the yield moments of the joints with recommended weld types were proposed and validated by both test and numerical analysis results, and additional formulas to check weld details were proposed for seismic design of bolted flange joints in prefabricated steel structures.