Weld Strength Research Articles

Effect of preloading force on capability of laser welding for skin tissue

Laser assisted suture has become a focus in surgical suture research due to its many advantages, but the current research on the details is not deep enough. To improve the strength and quality of laser biological tissue welding and increase the success rate of penetration in the thickness direction, the effect of external restraint force on the laser tissue welding was explored, and the effect of external restraint force on the optical properties of skin tissue was analyzed. In this study, a Nd:YAG pulse laser was used to conduct welding experiments on the skin in vitro. The laser of 10 W scanned the tissue incision along a linear trajectory. The welding effects under different compression forces and stretching forces were compared. Under the effect of compression force, the skin tissue incision has improved the absorption of laser, and achieved good suture of the incision. The maximum tensile strength can reach 15.56 ± 0.61 N/cm2.The results show that the external preloading force have a significant effect on the strength of the tissue under laser welding. The optical properties of skin tissue under different forces were tested, proving that compression force changes the absorption rate of skin tissue to laser, thereby promoting the photothermal conversion efficiency and improving the welding strength. The stretching force changes the thickness of the tissue, making it easier for the laser to penetrate. At the same time, the tissue is closely attached to achieve effective contact and improve the success rate of welding. The matching combination of preloading force and laser process parameters can achieve high strength with low thermal damage.

Evaluation of strength in stainless steel weld joints using ball indentation technique

In the present study, strength variations across the type 316LN stainless steel weld joints processed by advanced hot wire tungsten inert gas, activated tungsten inert gas, and hybrid laser metal inert gas welding processes were evaluated using automated ball indentation technique. The secondary dendrite arm spacing (SDAS) associated with welding heat input and welding thermal cycles strongly influenced the strength properties across the weld joints. The strength properties were lower at 823 K compared to 298 K because of thermally activated deformations. The hybrid laser metal inert gas welding process exhibited significantly narrower weld and higher strength in the weld and heat-affected zone due to finer SDAS and grain size, respectively, than the other weld joints.

Dual Material Fused Filament Fabrication via Core–Shell Die Design

In this work a fused filament fabrication (FFF) die design, capable of extruding two thermoplastics simultaneously in a core–shell configuration, is demonstrated as a means to produce composite structures in a single step. Despite the enormous advancements in 3D printing, fabrication of FFF objects with a composite structure remains a challenge due to the difficulty in finding dies to extrude such structures. We used polyethylene terephthalate glycol (PETG) and high-density polyethylene (HDPE) filaments to perform core–shell 3D printing. HDPE is one of the most commonly produced plastics but rarely used in FFF due to the severe warpage caused by volume changes upon its crystallization. Rheological and thermal analyses suggest the use of HDPE as a shell material due to its extremely short reptation time and sharp melting peak that facilitate superior surface contact and interlayer weld strength at the interface between neighboring FFF tracks. PETG is a commonly used 3D printing filament with excellent printability and sufficient zero shear viscosity to help maintain the extruded filament shape against shrinkage induced by the HDPE shell. Impact and tensile properties of core–shell objects revealed tremendous improvements in the impact resistance and toughness especially at 30 vol % HDPE shell with 1280% and 150% enhancement in impact resistance when compared to individual components: PETG and HDPE, respectively. Scanning electron microscopy was used to analyze the fracture morphology of the tested specimens to obtain an understanding of the fracture mechanism leading to the increased impact resistance. Using this die design can help open avenues of fabricating high impact resistance materials suitable for high performance applications and using HDPE in 3D printed objects with its superior solvent resistance.

Simultaneous optimization of weld bead geometry and weld strength during gas tungsten arc welding of Inconel 825 strips using desirability function coupled with grey relational analysis (DF-GRA)

Inconel 825 is a prominent Ni-Fe-Cr based superalloy finds application in aerospace, defense, automotive, nuclear, marine industries. This article investigates ‘weld strength’ and ‘weld bead characteristics’ of Inconel 825 weld specimens welded using the gas tungsten arc welding (GTAW) process. The welding speed (V), welding current (I), gas flow rate (GFR) and arc length (N) are considered as GTAW parameter and their effect has been examined on the weld characteristics. Welding speed and welding current has been identified as the most influential factor on process characteristics. Increased heat input from increased welding current and decreased welding speed initially improves weldment penetration (P) and ultimate tensile strength (UTS). However, at the highest heat input condition, the formation of root cracks is observed, resulting in nominal weld strength deterioration. To obtain a favorable parameters setting that satisfies both the criterion simultaneously i.e. maximizing weld strength for optimum weld bead geometry, a hybrid optimization approach employing desirability function coupled with grey relational analysis (DF-GRA) is proposed. Satisfying all the objectives simultaneously, the approach provides an optimum weld parameters setting of (I 3−V 1−GFR 2−N 1:120 A−180 mm min−1−9 l/min−2 mm) resulting an improvement of 4.15% in penetration (P), 5.12% in front width (W), 19.74% in reinforcement (R), 1.29% in ultimate tensile strength (UTS), and 2.9% in percentage elongation (%E) on validation. Upon comparison, the algorithm outperforms the optimization results of both DF and GRA approach suggesting its robust nature. Overall, the DF-GRA hybrid approach is found simple and effective that includes the ignored robustness of the desirability approach.

Study on fusion boundary microstructure and mechanical properties of austenitic stainless steel-nickel based dissimilar alloy materials welded joints

The metallographic test, microhardness test, and shear punch test of overlayer joint were carried out. The microstructure distribution and micro-zone mechanical properties of overlayer-girth weld fusion boundary (O-G), overlayer-austenitic (O-A) fusion boundary, and austenitic-grith weld fusion boundary (A-G) were studied respectively. At the same time, the type II boundary, DDC, and liquefaction crack were discovered. The results show that the microstructures on both sides of the O-G fusion boundary are γ phase and austenite-ferrite, respectively. There are three types of fusion limitations: type II boundary, direct fusion boundary, and transition fusion boundary. There are DDCs in the transition fusion boundary of the O-G zone, and liquefaction cracks caused by composition segregation in the inner of overlayer. The microstructures on both sides of the O-A fusion boundary are γ phase and uniaxial austenite, respectively, and there is no evident transition zone. Microstructures on both sides of the A-G fusion boundary are equiaxed austenite and austenite-ferrite (lath-skeleton-short rod). The average microhardness and shear strength of the O-A-G fusion border overlayer is the highest, 241 HV and 782 MPa respectively, and the microhardness decreases to 215 HV at DDCs defect. The microhardness and shear strength of base metal are 212 HV, 661 MPa, respectively. The microhardness and shear strength of the girth weld are 192 HV, 600 MPa, respectively. The maximum shear work of O zone is 1.62 J, and the minimum O-G fusion boundary is 1.12 J.

Prediction of Weld Tensile-Shear Strength using ANN Based on the Weld Shape in Aluminum Alloy GMAW

Weld shape and size generally determine the quality of gas metal arc welding. Auto parts manufacturers prescribe the size and shape of the weld because they can indicate the mechanical properties of the weld. It is impossible to evaluate the quality of all welds through destruction inspection. Therefore, research on welding quality inspection using laser vision sensors as a non-destructive inspection method is underway. Although the external profile of the weld can be measured using a laser vision sensor, studies to predict the weld strength are insufficient. In this study, an artificial neural network (ANN) model was developed to predict the welding strength of the lap-fillet weld of an aluminum alloy. Input date for weld size was obtained in two ways. In the first method, a bead profile was acquired using a laser vision sensor, whereas the size of the weld was obtained through the acquired bead profile. In the second method, the size of the weld was obtained directly from cross-section analysis. The output data on the strength of the weld was obtained through a tensile shear test. Two models for predicting the tensile shear strength based on ANN were developed. By predicting the tensile strength of both models, the average error rate was within 10%, but the prediction accuracy using the laser vision sensor was better than that of the cross-sectional method.

Investigation of welding defects in friction stir spot welding of plastics

In friction stir spot welding applications, there are some factors that provide welding strength, welding performance and the formation of defects that may occur in welding. Among these factors, machine parameters and welding tool design should be compatible with each other. If these factors are not chosen appropriately, the welding will not be of the desired quality. In this study, high density polyethylene sheets were joined using friction stir spot welding technique. It has been determined that some of the joints made have low weld strength, defects on the weld surface and around the stir zone. By investigating the causes of these defects, suggestions were made to prevent these defecs It has been observed that these defects are not repeated in the welds made with the suggestions made and it has been determined that high weld strength can be obtained. The highest weld strength and performance were obtained by 0.2–0.4 mm plunge depth, 45–60 s stirring time, 700–900 tool rotation speed and 30 mm shoulder diameters. In order to obtain a perfect weld in friction stir spot welding, it was determined that a homogeneous mixture should be formed between the stirring zone and the thermo-mechanically affected zone. Low weld strength was obtained in all joints with defects detected in these regions. Low weld strengths and weld defects were detected at dwell times of less than 30 s, at all tool rotational speeds with a stirring time of less than 45 s, at a plunge depth greater than 0.4 mm, and at low tool rotation speeds.

Metallurgical and mechanical properties of hydrogen charged carbide-free bainitic weld metals

Hydrogen embrittlement is a major concern during the welding of high-strength steels. The susceptibility of the welds to hydrogen embrittlement increases with increase in weld strength. The ever-increasing demand to increase the strength of steels necessitates the development of novel welding procedures and fillers to produce welds of high strength and with resistance to hydrogen embrittlement. In this current work, the susceptibility of carbide-free bainitic weld metals to hydrogen embrittlement is studied with varying volume fractions of constituent phases. Using three different weld metal compositions, six different weld metal microstructures of carbide-free bainite were generated. The hydrogen saturation behaviour of the various weld metals was studied by cathodic electrolytic charging and subsequent diffusible hydrogen measurements by the hot extraction method. Tensile tests were conducted on various weld metals with and without hydrogen charging to evaluate their susceptibility to hydrogen embrittlement. The results show that the carbide-free bainite weld metals are highly resistant to hydrogen embrittlement despite their very high strength.

Burr formation mechanism and morphological transformation critical conditions in grinding of nickel-based superalloy honeycomb cores

Nickel-based Superalloy Honeycomb (NBSH) is widely used in aerospace field due to the high temperature resistance, high specific strength and light weight. However, the NBSH is extremely prone to form burrs during processing. The unreasonable burr morphology causes insufficient welding strength or false welding between NBSH and skin, resulting in premature failure of the parts. Hence, the burr formation mechanism and morphological transformation critical conditions in grinding NBSH were investigated based on finite element method (FEM) and experiments. Furthermore, the orthogonal experiments were carried out to investigate the effects of grinding parameters on burr and obtain the suitable parameter intervals to restrain the flash burr formation. The results indicate that due to the absence of supporting material, the extruded material of edge transforms into the Fourth Deformation Zone (FDZ). The FDZ rotates a certain angle due to the extrusion of abrasive particle, which leads to the fact that the FDZ cannot be removed and remains on the honeycomb wall, thus forming micro burr. If the material removal per unit time is large, the chip is not removed from FDZ. The parts that should have been chips are bonded with micro burr to form a flash burr. To restrain the flash burr formation, the suitable intervals of grinding depth, grinding speed and feed speed are 5–15 μm, 60–70 m/min and 500–1000 mm/min, respectively.

Submerged ultrasonic plastic welding: A computational and experimental investigation

Thermoplastics hold utmost importance in the day-to-day life of modern-day society, being widely employed in water transport and storage vessels commonly made from thermoplastics such as PVC, i.e., polyvinyl chloride, and PP, i.e., polypropylene. This urge for a joining technique is applicable even with water in the vessel or the submerged case. The present investigation explores ultrasonic welding as an option to weld thermoplastics in water-submerged conditions. We have performed FEM simulations and experimental validation to prove the viability of the proposed ultrasonic welding process used in welding PVC and PP in water-submerged conditions. The discussed results demonstrate a decrease in melting and degradation of adherend material at the weld interface while welding PVC and PP in water-submerged conditions and attaining 65.78% and 107% of weld strength, unlike their open-air counterparts, respectively.

Investigating the Welding Parameters in Friction Stir Welding of Yellow Brass 405-20

This research presents the numerical and empirical efforts to investigate the effect of friction stir welding (FSW) parameters on the weld temperature, weld strength, and weld hardness for novel brass known as yellow brass 405-20. The numerical approaches used to measure the weld temperature and weld strength were studied for the first time for yellow brass 405-20 and their validations via empirical studies. Two numerical models were simulated including transient thermal analysis and static structural analysis. Thermal distribution leading to maximum weld temperature during FSW of yellow brass was investigated via both simulations and experiments. Moreover, the ultimate tensile strength, namely the weld strength, was measured numerically and validated from its empirical counterpart. Finally, weld hardness was measured empirically to explore the joint health. A maximum temperature of 598 °C was recorded, which was much below the melting point of brass. Joint strength of 228 MPa was observed, which is 83% of the base brass strength. Microscopic examination of the weldment revealed the underlying mechanisms of less weld strength as compared to the parent brass material strength.

Mechanical properties of high strength steels and weld metals at arctic low temperatures

This paper attempts to acquire fundamental knowledge on the mechanical properties of high strength steels and the corresponding high strength weld metals at arctic low temperatures. Two types of high strength steels (Q890, Q960) and three types of high strength weld metals (made of ER100S-G, ER110S-G, ER120S-G feedstock wires) were tested at arctic low and ambient temperatures ranging from −75 °C to 25 °C. Tensile coupon specimens for steel materials were directly extracted from high strength steel plates, whilst robotic gas metal arc welding was employed to fabricate the tensile specimens of weld metals. The tensile coupon specimens were designed as per ASTM E8M and wire-cut into shapes. Twenty-three tensile coupon tests on high strength steels and eighteen tensile coupon tests on high strength weld metals were carried out. Coupon specimens were tested in liquid nitrogen cooling chamber to mimic the arctic low temperature environment. The stress–strain responses and key mechanical properties of high strength steels and weld metals at both ambient and arctic low temperatures are presented and discussed. Prediction equations for key mechanical properties, including the Young’s modulus, yield stress and ultimate tensile strength, of high strength steels and weld metals at arctic low temperatures were proposed.

Joint performance of medium carbon steel-austenitic stainless steel double-sided TIG welds

Abstract AISI 1040 and AISI 304 steel plates of 10 mm were joined without pretreatment by double-sided TIG arc welding (DSAW). Joints were manufactured by using welding currents of 420, 440, and 460 A. The microstructural variations in the interface of the weld samples were defined by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and microhardness analysis. V-notch impact and tensile tests were done to detect the weld strength of the weld samples. In DSAW welding of different steels, a full penetration joint was achieved without opening the weld edge. The current intensity had a major effect on the symmetrical and hourglass shape in welds. Welding at 460 (A) showed acceptable joint quality. Tensile and impact energy quantities of welded joints had significant ratios. Fractures in the weld metal of the samples were ductile mode.

Evaluation of strain based ECA method in DNVGL-RP-F108

Pipelines may be subject to strain-controlled external loads exceeding yield strength of materials due to many causes, e.g., soil settlements and ground movement. There are several strain based fracture mechanics assessment methods to determine the maximum tolerable defect sizes in girth welds in pipelines. One of these methods is the DNVGL-RP-F108 procedure which was developed from a joint industry project for assessing reeled pipes and has been used for both offshore and on-shore pipelines. However, as with other methods, it requires the weld strength either even- or over-matching the parent steel which may be difficult to achieve for high strength steels. There are also uncertainties about the adequacy of the DNVGL-RP-F108 guidance addressing the effects of internal pressure and welding-induced residual stresses. In this study, the maximum tolerable defect sizes in the girth welds of an X70 spiral welded pipeline were determined using the DNVGL-RP-F108 approach. The effects of several variables on the assessment results, including weld strength mismatch, stress-strain curve magnitude, internal pressure level, fracture toughness, residual stresses and misalignment, were also investigated. A comprehensive finite element analyses were performed to verify the crack driving force determined by the DNVGL-RP-F108 approach. It was found that the DNVGL-RP-F108 approach can be conservatively applied to girth welds with a weld strength under-match by 5% in all cases, and even by 10% for most cases, for the conditions investigated. It was also revealed that use of this guidance could be unduly conservative for strength over-matching welds.

Large depth to width ratio friction stir welding joint obtained by novel designed tool with double pin

A novel welding tool with a double pin structure was proposed to solve the problem of difficult weld formation with a large depth to width ratio (DWR). Experiments revealed that the novel welding tool could achieve non-defect joints for four common engineering aluminum alloys (2A12-T6/5052-H32/6013-T6/7075-T6), with a DWR of 0.59–0.67. Due to the difference in the direction of material flow between the upper pin and the pin effect, impact slow flow zone was formed in the joint center. The maximum ultimate tensile strength of the 7075-T6 aluminum alloy double pin friction stir welding (DPFSW) joint reached 450.38 MPa, which was 85.8% of the base material. Analysis of the tensile fracture location revealed that the stirring zone of the advancing side and weld nugget zone occurred local blockage, resulting in joint failure. • In this paper, a novel welding tool with a double-pin structure is proposed, and it is demonstrated through experiments that the novel welding tool can achieve defect-free joints with DWR of 0.59–0.67 for four common engineering aluminum alloys. • The DPFSW joint can be divided into seven zones, where the ISFZ is caused by the different flow directions of the upper and lower layers of the DPFSW material, and the interior of this zone consists of a mixture of fine and coarse grains. • The numerical simulation results are consistent with the actual tensile results and the modeling is reasonable. PA and PB are the locations where partial blockage occurs in SZ-AS and UWNZ/DWNZ, which are the weak zones of the joints. • DPFSW joints are greatly influenced by the welding speed. At a welding speed of 100 mm/min, the joint strength was the highest, reaching 450.38 MPa, or 85.8% of BM.

Prediction of the Ultimate Tensile Strength (UTS) of Asymmetric Friction Stir Welding Using Ensemble Machine Learning Methods

This research aims to develop ensemble machine-learning methods for forecasting the ultimate tensile strength (UTS) of friction stir welding (FSW). The substance utilized in the experiment was a mixture of aluminum alloys AA5083 and AA5061. An ensemble machine learning model was created to predict the UTS of the friction stir-welded seam, utilizing 11 FSW parameters as input factors and the UTS as a response variable. The proposed approach used the Gaussian process regression (GPR) and the support vector machine (SVM) model of machine learning to build the ensemble machine learning model. In addition, an efficient technique using a differential evolution algorithm to optimize the weight for the decision fusion was incorporated into the proposed model. The effectiveness of the model was evaluated using three datasets. The first and second datasets were divided into two groups, with 80% for the training dataset and 20% for the testing dataset, while the third dataset comprised the test data to validate the model’s accuracy. The computational results indicated that the proposed model provides more accurate forecasts than existing methods, such as random forest, gradient boosting, ADA boosting, and the original SVM and GPR, by 30.67, 49.18, 16.50, 48.87, and 49.33 %, respectively. In terms of prediction accuracy, the suggested technique for decision fusion surpasses unweighted average ensemble learning (UWE) by 10.32%.

Consumable pin-friction stir spot welding of Al-Mg-Si alloy via pre-created hole and refilling: Microstructure evolution, defects, and shear/tensile failure load

Since Al-Mg-Si alloys are widely used in the transportation industry, it is important to produce a sound and robust weld between the sheets of these alloys. The focus of this work is on the tensile-shear and cross-tension strengths of the consumable pin-friction stir spot welds (CP-FSSWs) without an exit-hole between the Al-6061 aluminum sheets. Before welding, a hole was created at the joint region in the base sheets and then, it was filled using a rotating consumable pin. The tensile-shear, cross-tension, and microhardness tests were employed to evaluate the mechanical properties of the spot welds. The results showed that the pre-created hole was entirely filled during the welding process. While a complete bond was formed between the consumable pin and the lateral surface of the hole, there were three distinct regions at the interface of the pin and the bottom of the hole: complete bond, kissing bond, and defects. Enhancement of the tool rotational speed decreased the area of the complete bond in the weld compared to the other regions. A linear relationship existed between the bonding area and weld failure load in the cross-tension test. The proposed relationship approved the impact of the swirly region at the interface of the base sheets on the weld strength. While in the cross-tension test, the weld failure load decreased from ∼2800 to ∼1950 N, it improved from ∼10,500 to ∼12,000 N in the tensile-shear test with enhancement of the tool rotational speed from 700 to 2000 rpm. The hardness measurements demonstrated that there was no common heat affected zone softening after CP-FSSW.

PENGARUH POSISI SHIELDED METAL ARC WELDING (SMAW) GERAK SPIRAL KAMPUH V TERHADAP KEKUATAN TARIK DAN STRUKTUR MIKRO BAJA KARBON RENDAH

The purpose of this study was to determine the relationship between the position of shielded metal arc welding (SMAW) with spiral motion V on the tensile strength and microstructure of low carbon steel. The research was conducted by welding V-coated low carbon steel with horizontal 2G, vertical 3G and overhead 4G. The test results show that the welding position does not have a significant effect on the tensile strength of low carbon steel welds, where the 3G vertical position provides a higher tensile strength value than the 2G horizontal position and 4G overhead. The microstructure of acicular ferrite (AF) in the vertical position looks dominant uniformly and tightly.

Investigation of Intermetallics Formation and Joint Performance of Laser Welded Ni to Al

In this paper, laser welding Ni to Al using pulsed wave (PW) and continuous wave (CW) lasers was investigated. Weld quality and strength were evaluated in terms of cross-section examination, intermetallic compounds formation, microhardness, shear test and 90-degree peel test. The results show that deep penetration welding Ni to Al causes high melting pool temperature and severe material mixing, which could result in dominant AlNi3 and AlNi intermetallics (IMCs) in the weld. These IMCs could significantly increase the hardness of the welding zone, but could also lead to the formation of defects, as well as reducing the ability to withstand the shear force and peel force applied to the weld. In comparison, using process optimization to maintain a shallow penetration or form a weld-braze joint, low melting pool temperature and minimum material mixing can be achieved. Hence, low-hardness Al3Ni IMCs are prevalent in the weld. This helps generate a defect-free dissimilar weld joint to withstand higher shear force and peel force. The findings show promising applications, such as the battery management system of electric vehicles, in which joining a Ni adaptor to an Al bus bar is required.

Phenomenological 2D and 3D Models of Ductile Fracture for Girth Weld of X80 Pipeline

Welding is the main method for oil/gas steel pipeline connection, and a large number of girth welds are a weak part of the pipeline. Under extremely complex loads, a steel pipeline undergoes significant plastic deformations and eventually leads to pipeline fracture. A damage mechanics model is a promising approach, capable of describing material fracture problems according to the stress states of the materials. In this study, an uncoupled fracture 2D model with a function of fracture strain and stress triaxiality, two uncoupled 3D fracture models, a consider the effect of Lode parameter stress-modified critical strain (LSMCS) model, and an extended Rice–Tracey (ERT) criterion were applied to X80 pipeline girth welds. Comprehensive experimental research was conducted on different notched specimens, covering a wide range of stress states, and the corresponding finite element models were established. A phenomenon-based hybrid numerical–experimental calibration method was also applied to determine the fracture parameter for these three models, and the stress triaxiality of the influence law of the tensile strength was analyzed. The results showed that the proposed fracture criterion could better characterize the ductile fracture behaviors of the girth welds of the X80 pipeline; however, the prediction accuracy of the 3D fracture model was higher than that of the 2D fracture model. The functional relationship between the tensile strength and stress triaxiality of the X80 pipeline girth welds satisfied the distribution form of the quadratic function and increased monotonically. The research results can be used to predict the fracture of X80 pipeline girth welds under various complex loads.