Weld Failure Research Articles

Mechanics and complications of reverse shoulder arthroplasty: morse taper failure analysis and prospective rectification

Since Sir John Charnley began his monumental hip arthroplasty work in 1958, clinical researchers have been incrementally improving longevity and functionality of total joint systems, although implant failure occurs on occasion. The purpose of this study is to report the fracture of the humeral tray Morse taper of a reverse total shoulder system (RTSS), which to date has not been reported with metallurgic analysis for any RTSS. There was no reported antecedent fall, motor vehicle collision, or other traumatic event prior to implant fracture in this case. Analysis was performed on the retrieved failed implant by Scanning Electron Microscopy (SEM) and Electron Dispersion Spectroscopy (EDS) in an attempt to determine the failure method, as well as to offer improvements for future implants. At the time of revision surgery all explants were retained from the left shoulder of a 61-year old male who underwent a non-complicated RTSS 4 years prior. The explants, particularly the cracked humeral tray, were processed as required for SEM and EDS. Analysis was performed on the failure sites in order to determine the chemical composition of the different parts of the implant, discover the chemical composition of the filler metal used during the electron beam welding process, and to detect any foreign elements that could suggest corrosion or other evidence of failure etiology. Gross visual inspection of all explants revealed that implant failure was a result of dissociation of the taper from the humeral tray at the weld, leaving the Morse taper embedded in the humeral stem while the tray floated freely in the patient’s shoulder. SEM further confirmed the jagged edges noted grossly at the weld fracture site, both suggesting failure due to torsional forces. EDS detected elevated levels of carbon and oxygen at the fracture site on the taper only and not on the humeral tray. In order to determine the origin of the high levels of C and O, it was considered that in titanium alloys, C and O are used as stabilizers that help raise the temperature at which titanium can be cast. Since the presence of stabilizers reduces ductility and fatigue strength, all interstitial elements are removed after casting. Considering this, the presence of C and O suggests that not all of the interstitials were removed during the manufacturing process, resulting in decreased fatigue strength. Further destructive analytical testing would verify weld quality and failure mode. RTSSs are quite successful in select patients not amenable to traditional shoulder arthroplasty options. This case report highlights how an implant may function well for several years and then suddenly fail without warning. SEM and EDS analysis suggest that residual C and O in the taper lowered the metal implant’s integrity, leading to torsional cracking at the weld junction of the humeral tray and the taper. The elevated levels of C and O measured at fracture sites on both the tray and the taper suggest poor quality filler metal or failure to remove all interstitial elements after casting. In both cases, the results would be decreased fatigue strength and overall toughness, leading to mechanical failure. A manufacturer’s recall of all implants soon followed the reporting of this implant failure; subsequently, the metal materials were changed from Ti6Al4V to both titanium alloy and cobalt-chrome alloy (Co-Cr-Mo). Time will tell if the alterations were sufficient.

Numerical Analysis and Testing of Tungsten Inert Gas Welded T-Joints

Presently arc welded structures are extensively used in automobiles, constructions and power plants. As the main cause of weldment failure is design defect and overload, it is necessary to analyze the maximum stresses in the weldment. This work deals with investigation of welded T-joint by Tungsten Inert Gas (TIG) welding process with varying gap and angle between the parent materials to determine the breaking stress under tensile load in the weldment. Finite element analysis is carried out using Ansys software and results are compared with experimental analysis using Taguchi optimization method. Angle, arc force and gap between parent materials are used for the Taguchi optimization technique. The optimized fillet weld section (low carbon steel AISI1020 and copper) is arrived by restricting the weldment failure.

Study of Weld Integrity and Nugget Development in Seam-Welded Cold-Rolled High-Strength Steels

Production processes like continuous annealing and continuous galvanizing/galvannealing rely on welding of two strips across their width, for continuous operation. The operational stability of these lines depends highly on the consistency of the welding process. Any failure of weld joint during processing is detrimental to production as the recovery times are very high (~1–3 days). Two instances of similar weld failures having identical chemical composition and dimensions of the strips were investigated to identify the root cause and establish adequate countermeasures. A systematic approach to evaluate weld performance using metallographic examination was carried out. The examinations revealed that poor nugget formation was the root cause of failure. The nugget formation, its orientation and size were also evaluated after carrying out a series of trials with different welding process parameters, and an optimum condition was arrived at. In summary, the weld failure occurred due to insufficient and unbalanced nugget formation which could be rectified by modifying the welding parameters such as current, pressure and speed.

Experimental assessment of the composite joints shear connector component

One of the methods adopted for the composite semi-rigid beam to column joints characterization is the component method present in the Eurocodes 3 and 4 that considers the composite action in the model by incorporating the component contributions of the reinforcing bars, concrete and shears connectors. However, the model is based on not fully validated assumptions of the composite joints structural response mainly located in hogging moment regions. All these aspect have limited the adoption of this method for composite joints design. These issues motivated the conception and development of an experimental programme to investigate semi-rigid beam to column joints, by means of pull out tests. The present paper focus on tests that presented failure modes associated to the shear connector failure. Additionally a study was also made on the resistance of shear connector welds. This investigation was provoked to some observed shear connector weld failures in a few pull out tests. The tests results enabled a better understanding of the shear connector weld resistance and their impacts and influence over the global semi-rigid beam to column joints structural response.

Optimization of Welding Parameters, Influence of Activating Flux and Investigation on the Mechanical and Metallurgical Properties of Activated TIG Weldments of AISI 316 L Stainless Steel

This research investigation articulates the joining of AISI 316 L austenitic stainless steel plates of thickness 5 mm by activated tungsten inert gas (A-TIG) welding. Prior to the welding, the optimization of process parameters and the selection of suitable flux have been carried out to join the plates in a single pass welding. The experimental results show that the complete weld penetration can be achieved by using activating flux. The microscopic study divulges the presence of delta ferrite, sigma phase and various forms of austenite in the weld zone. Fischer Feritscope result indicates that the delta ferrite content in the weld is higher (7.8 FN) than the base metal (1.3 FN) which results in superior mechanical properties of the weld. Field Emission-Scanning Electron Microscope (FE-SEM) fractography reveals that the failure of weldments occurs in ductile mode. 180° bend test study reveals the good ductility of the joint.

Root cause analysis and reliability improvement methods for orbital TIG welding process for propulsion feed system of satellites

The orbital tungsten inert gas welding is extensively used in space application such as welding of propellant feed lines and components of the propulsion sub system of satellite, space recovery module and crew module etc. The feed lines are made up of 6 or 10 mm diameter stainless steel tubes of 0.7 mm thickness which are very critical for the successful operation of propulsion system of the satellite. This paper focuses on the root cause analysis and reliability improvement of the orbital TIG welding process. Procedures such as failure modes effects and criticality analysis, cause and effect diagram, fault tree analysis (FTA) and Pareto analysis (PA) are applied to analyze the basic problems encountered with orbital TIG welding to find out critical process failure modes, their causes and remedial actions that can be suggested for process improvement. Cause effect diagram of the welding process is drawn to understand the important parameters such as current, Revolution per minute (RPM), shield gas flow, gap between electrode and tube, gap between tubes, cleanliness etc. causing weld failures. Root cause analysis is carried out using FTA for identification of basic events and their combination effect leading to the weld failure. Further, PA helps to find out which are all the most affecting factors of the process. By implementing these reliability analysis techniques, it is possible to improve the reliability of orbital TIG welding process for propellant feed systems for satellites.

Macro-modeling of the strength and failure of multi-layer multi-steel grade spot welds: Connector formulation, assembly model and identification procedure

The aim of this paper is to investigate the mechanical strength and the failure of three-sheet multi-steel grade Resistance Spot Welded assemblies (RSW) using experimental and numerical tests. A macroscopic modeling approach, using three connector elements, dedicated to the crashworthiness analysis is therefore proposed. The proposed model involves parameters that have to be set. To simplify and to reduce the optimization problem, direct and inverse identification approaches are proposed. The numerical results are in good agreement with the experimental ones for both pure and combined Arcan tests for the different studied configurations.

Examination of Mode I Loading on Resistance Spot Weld Groups in Tailored Hot Stampings

In this work, Mode I fracture of single and grouped resistance spot welds in hot stamped steels for automotive applications were examined. Fully quenched and 400oC tailored Usibor® 1500-AS samples were used to create flat sheet and hat channel specimens which were resistance spot welded. To characterize the material constituent distribution throughout the parts, hardness measurements were taken. While a large amount of work has been done to characterize tailored hot stampings, spot weld failure is not well understood. The problem is particularly acute for weld failure in structural components where groups of welds may fail in an unstable unzipping mode. To that end, coupon and structural Mode I testing was conducted where force, displacement, and visual data were sampled throughout the test events. While ductility appeared to have little effect on the strength of a single weld, it largely affected the structural response.

Analysis of Optimum Butt Welded Joint for Mild Steel Components Using FEM (ANSYS)

Weld failure due to vibrations can be minimized if appropriate measure is implemented to ensure forced vibration is not equal to the natural frequency of the material. This research focuses on determining the optimum butt welded joint, by analyzing the various natural frequencies and mode shape response obtained from five different types of butt joints. In this study, modal analysis was carried out using ANSYS 14.5 on two mild steel plates of dimensions 250mm by 175mm by 25mm welded together. Five different geometries of butt joints namely: single V groove butt weld, double V groove butt weld, single U groove butt weld, double U groove butt weld and square groove butt welded joints were examined. The natural frequencies and mode shape deformations obtained were compared with the natural frequency of mild steel of zero weld plate of dimension 500mm by 175mm by 25mm. Natural frequency of zero weld plate was found to be 51.549Hz, it was observed that the natural frequencies of the five joints mentioned were of close range in increasing order of 45.020Hz, 47.949Hz, 48.506Hz, 49.264Hz and 50.342Hz for square groove butt welded joint. The natural frequency of the square groove butt welded joint was observed to be closest to the zero weld plate; therefore we recommend square groove butt weld as optimum butt weld for engineering constructions because it failed the least when compared to other types of butt joints.

Investigations on weld metal chemistry and mechanical behaviour of bimetallic welds using CaO–CaF2–SiO2–Ni based electrode coatings

The bimetallic welds between ferritic low alloy steels and austenitic stainless steels are widely used in the heat piping transport systems of nuclear power plants for connecting the heavy section low alloy steel components with those of high temperature stainless steel pipes. The operating experience of major nuclear power plant components has recently shown that bimetallic joints can jeopardize the plant availability and safety because of increased incidences of failure. In shielded metal arc welding process, the occurrence and severity of weld defects mainly depend upon the type of electrode filler wire and the electrode coating ingredients used. The use of nickel based filler metals is no longer considered as the final solution for unexpected failures of bimetallic welds due to incidences of hot cracking. In the present paper, an attempt has been made to design and develop an intermediate electrode based on CaO–CaF2–SiO2 ternary phase diagram system and nickel as an additional electrode coating ingredient using mild steel as a filler wire for the bimetallic weld joint. The extreme vertices methodology has been used to design 21 electrode coating formulations. The quadratic regression models for weld metal chemistry, ultimate tensile strength, impact toughness, macrohardness, diffusible hydrogen content, and corrosion rate in terms of electrode coating ingredients, have been developed and checked for adequacy using analysis of variance. The work aims at studying the individual as well as combined effect of electrode coating ingredients on the measured weld responses and microstructures of the weld. Also, the electrode coating formulations suggesting multiobjective optimized solutions have been proposed.

Influence of polarity on mechanical properties of dissimilar resistance spot welds of DP 600/AISI 304 steels

The influence of polarity during resistance spot weld (RSW) of dissimilar lap joints on mechanical properties and failure mode is assessed in this work. A dissimilar lap joint was set using DP 600 dual phase steel with AISI 304 stainless steel. The experiments were performed on a medium-frequency direct current spot welding machine with proper data acquisition of voltage and welding current. Temperature evolution was also acquired by using IR camera. The mechanical properties of spot welds were evaluated by using a coach peel testing. The effect of welding current and welding time on mechanical properties was also evaluated. Correlations between polarity with the welding nugget size, failure mode, tensile strength, temperature evolution and dynamic resistance were analysed. The analysis confirmed that the polarity on dissimilar lap joints affects the behaviour of dissimilar RSWs.

On the resistance spot welding of four-sheet stack of unequal sheet thickness

There is a lack of sufficient understanding regarding resistance spot welding behaviour of multi-layer structure. This paper investigates the weld nugget development and failure characteristics of four-sheet joint of dissimilar sheet thickness (0.7/1.2/1.2/0.9 mm) made on low carbon steel. The heat dissipation via water-cooled electrode hinders the weld nugget penetration into the thin/thick sheet interface. It was shown that increasing heat input led to bonding mechanism transition from solid-state welding to fusion welding at thin/thick sheet interface. Increasing welding current beyond a critical value changed the failure mode from interfacial to pullout leading to improvement of energy absorption of the joint. Fusion zone size along middle sheet/sheet interface proved to be the most important controlling factor for mechanical properties of four-sheet resistance spot welds.

Characteristics of Welding Crack Defects and Failure Mode in Resistance Spot Welding of DP780 Steel

The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested, and three different types of welding cracks in welded joints were investigated by optical microscopy, scanning electron microscopy and electron back-scattered diffraction. Finally, the failure mode of the welded joints in shear tensile test was discussed. It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current. The surface crack in welded joint is intergranular fracture, while the inner crack in welded joint is transgranular fracture, and the surface crack on the edge of the electrode imprint can be improved by adding preheating current or tempering current. The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.

Fitness for Purpose Assessment of Girth Weld Defect Based on In-Line Inspection

The girth weld defect is one of the most common types of defects on oil and gas pipelines, which can have a strong impact on the operation safety. Several girth weld failure accidents have occurred on PetroChina’s pipelines in recent years. In this paper, PetroChina’s current work on inspection and fitness for purpose assessment of girth weld defects is summarized. The in-line inspection has been proved to be the best practice for oil and gas pipeline defect inspection, but there are still some technical issues such as defect characterization and parameter selection. Fitness for purpose assessment methods for girth weld defects include strength assessment method based on plastic collapse, FAD method based on both plastic collapse and fracture, simplified factor method and numerical analysis method based on finite element. It is critical to identify the actual type of defects detected in in-line inspection to select an appropriate assessment method. The identification of various loads and the selection of appropriate material parameters are also important issues in assessment procedure. The key techniques to be developed include defect characterization, load identification, assessment of defects on high grade steel pipes, reliability-based assessment, etc.

Postcrack Propagation of Tensile Shear Test: Analyzing the Carbon Steel Welds, Stainless Steel Welds, and Both Steels Mixed Welds in Resistance Spot Welding

Conducting tensile shear test for the spot-welded specimens is a common practice in resistance spot welding as it helps to understand the loading behavior and its corresponding effect. Two categories of weld failures are conventionally regarded, as to distinguish the sound weld over a poor one. This approach has severe drawback from early days and therefore the postcrack propagation (PCP) method is carried out as an alternative in this experimental study. With the PCP experimental results in hand, the tensile shear test is simulated using ANSYS to observe the corresponding strain distribution. Based on the visual inspection of simulation and practical results, three classifications (IF, PF, and TF) are consequently categorized; so that the weld failures of tensile shearing test can now be accurately distinguished by means of cracking patterns. Moreover, some degrees of fractures have regularly been noticed by other fellow researchers within these three categories and thereby the fractures have been named after the degrees of cracking severity. Carbon steel welds, partially corroded carbon steel welds, stainless steel welds, and mixed steel welds have been parallelly analyzed for the PCP modes and the results obeyed the categorization very well.

Experimental study on uniaxial tensile and welding performance of a new coated fabric for airship envelopes

This paper investigated the mechanical properties of GQ-6 subjected to a tremendous amount of uniaxial tests. Such material is a new kind of ultra high molecular weight polyethylene fiber and aimed to be adopted in stratospheric airship. To begin with, mono-uniaxial tensile tests were conducted. The cycling-uniaxial tensile experiments were then carried out on the basis of the mono-uniaxial tensile tests data. Finally, performances of welding seams were thoroughly investigated with forty welding specimens. Results of mono-uniaxial tensile tests revealed that such woven fabric possesses high tensile strength and low elongation ratio at break. Meanwhile, the stress–strain behaviors were fitted by the Ogden model and a good agreement between such model and experimental data was obtained. Influences of the uniaxial loading cycle on such woven stiffness were discussed and the elastic moduli were defined with a standard hysteresis loop. For the welding tests, four types of overlapping welding failures were discovered. Compared with intact specimens, an appropriate welding width of 60 mm and an approximate 15% discount of the ultimate tensile stress on the intact textile were obtained.

Shock response of filled corrugated sandwich structures under extreme temperatures

Shock tube experiments were performed to investigate the blast response of corrugated steel cellular core sandwich panels filled with a silicone based syntactic foam at room and high temperatures. The syntactic foam filler was prepared by mixing a two-part silicone mixture with glass microspheres; its microstructure, and mechanical properties were also characterized. The syntactic foam-filled sandwich panels were loaded via air shock pressure by using the shock tube with a fixture capable of testing materials at temperatures up to 900℃. High-speed photo-optical methods, digital image correlation techniques, were used in tandem with optical band-pass filters and high intensity light sources for providing sufficient contrast at elevated temperatures. Back-face deformation images were captured using two synchronized high-speed cameras while a third camera captured the side view deformation images. The shock pressure profiles and digital image correlation analysis were used to obtain the impulse imparted to the specimen, transient deflection, in-plane strain and out-of-plane velocity of the back-face sheet. It was observed that using the syntactic foam as a filler material decreased the front face and back face deflections by 42% and 27%, respectively, as compared to the empty sandwich panel. At high temperatures, the silicone-based syntactic foam decomposes into silica, a stable and non-hazardous byproduct. The highest impulse was imparted to the specimen at room temperature and subsequently lower impulses with increasing temperatures were observed. Due to the increased ductility of steel at high temperatures, the specimens demonstrated an increase in back face deflection, in-plane strain and out-of-plane velocity with increased temperatures, with weld failure being the primary form of core damage.

Failure of Stainless Steel Welds Due to Microstructural Damage Prevented by In Situ Metallography

Abstract In stainless steels, microstructural damage is caused by precipitation of chromium carbides or sigma phase. These microconstituents are detrimental in stainless steel welds because they lead to weld decay. Nevertheless, they are prone to appear in the heat affected zone (HAZ) microstructure of stainless steel welds. This is particularly important for repairs of industrial components made of austenitic stainless steel. Non-destructive metallography can be applied in welding repairs of AISI 304 stainless steel components where it is difficult to ensure that no detrimental phase is present in the HAZ microstructure. The need of microstructural inspection in repairs of AISI 304 is caused because it is not possible to manufacture coupons for destructive metallography, with which the microstructure can be analyzed. In this work, it is proposed to apply in situ metallography as non-destructive testing in order to identify microstructural damage in the microstructure of AISI 304 stainless steel welds. The results of this study showed that the external surface micrographs of the weldment are representative of HAZ microstructure of the stainless steel component; because they show the presence of precipitated metallic carbides in the grain boundaries or sigma phase in the microstructure of the HAZ.

Failure analysis of girth weld cracking of mechanically lined pipe used in gasfield gathering system

Abstract Girth weld cracking of mechanically lined pipe was occurred after 75 days operation in a gasfield gathering system in China. Failure causes were analyzed based on operation histories, field documents, and laboratory tests. Results showed that the girth weld failure was mainly due to two aspects, girth weld martensite microstructure and external stress. The crack was initiated from sealing pass zone and filling pass zone, which is a hard and brittle martensite structure with hardness of HV 350–450. The failed pipe area had undergone the heavy rain for 2 days, pulling stress, bending stress, and shear stress generated by soil movement resulted in high stress concentration at girth weld. The girth weld cracking failure was initiated from outer carbon steel, and propagated along the weld-fusion line in intergranular mode, which is a typical stress corrosion cracking failure.

Investigation of the Failure of Advanced High Strength Steels Heterogeneous Spot Welds

Nowadays, environmental regulation encourages carmakers to reduce the global vehicle weight. Steelmakers develop grades with high performance (Advanced High Strength Steels, AHSS) and fine steel sheet assemblies are used in car body structures, with an optimized thickness in each part. However, unusual fracture modes are sometimes observed during the mechanical tests of heterogeneous AHSS welds, made of dissimilar steel grades and sheet thicknesses. Weld fractures can occur with a strength lower than expected. This study aims at understanding these fracture mechanisms and focuses on two common steel grades joined by Resistance Spot Welding (RSW): DP600 (a dual phase steel) and Usibor®1500 (a martensitic steel). The parameters affecting the failure modes and load bearing capacity are investigated during two common types of tests: the Cross Tension and Tensile Shear tests. The positive effects of heterogeneous welding with respect to the corresponding homogeneous configurations are discussed, as well as the consequences of a so-called Dome failure occurring at the weld nugget boundary.