Shear Strength Of Joints Research Articles

Performance of the GH4169 Joint Using a Novel Ni-Based Amorphous Brazing Filler Metal

A novel Ni-Cr-Si-B filler metal (JNi-5) was designed and further fabricated into the amorphous brazing filler metal for joining the GH4169 alloy. The effect of brazing temperature on the microstructure and mechanical properties of GH4169 joints was investigated. The typical microstructure of the joint at 1030 °C is composed of four specific zones: the base metal (BM), heat-affected zone (HAZ), isothermal solidification zone (ISZ), and athermal solidification zone (ASZ). The typical microstructure of the joint is GH4169/(Nb, Mo)-rich boride+(Cr, Nb, Mo)-rich boride/γ(Ni)/Ni-rich boride+γ(Ni)/γ(Ni)/(Cr, Nb, Mo)-rich boride+(Nb, Mo)-rich boride/GH4169. As the temperature increased, the HAZ continued to widen and the ASZ depleted at 1090 °C and 1120 °C. Additionally, the borides within the HAZ coarsened at temperatures of 1090 °C and 1120 °C. At 1030 °C, the fracture path is in the ASZ, and the existence of the brittle phase in the ASZ provides the potential origin for crack growth. The fracture mode is a quasi-cleavage fracture. At 1060 °C, 1090 °C, and 1120 °C, the fracture behavior mainly happened in the HAZ, and the existence of borides in the HAZ provides the potential origin for crack growth. Namely, the shear strength of joints was principally dominated by the brittle precipitations in the HAZ. The fracture mode of these joints is the hybrid ductile. At 1060 °C, the shear strength of the obtained joint is the highest value (693.78 MPa) due to the volume fraction increase in the Ni-based solid solution. Finally, the optimized brazing parameter of 1060 °C/10 min was determined, and the corresponding highest shear strength of 693.78 MPa was obtained owing to the increased content of the Ni-based solid solution in the joint.

Enhancing resistance welding strength of carbon fiber/polycaprolactam thermoplastic composites through coupling agent‐modified metal heating elements

AbstractThis study investigates the impact of coupling agent‐modified resistance welding heating elements on the welding strength of carbon fiber‐reinforced polyamide 6 (PA6) thermoplastic composites. Silane coupling agent KH550 and titanate coupling agent UP‐201 were used to modify heating elements made of 304 stainless steel mesh. Optimal modification parameters for KH550‐modified stainless steel mesh (SSM) were determined using orthogonal experiments, resulting in maximum single lap shear strength (LSS) of 17.05 MPa under specific welding conditions. Comparative tests demonstrated the enhancement effect of UP‐201‐modified SSM on LSS. Additionally, two experimental schemes were used to study the synergistic enhancement effect of KH550 and UP‐201 on the LSS of resistance welded joints. The findings indicate that both coupling agents improve the welding strength, with significant differences in their individual and combined effects.Highlights This study explores carbon fiber reinforced Nylon 6, an innovative thermoplastic. Analyzed effects of modified heating elements on joint shear strength. Examined silane and titanate coupling agents' effects on weld joint shear strength. Investigated synergistic effects of silane and titanate agents on weld joint strength. Investigated the synergistic enhancement mechanism of silane and titanate agents.

Investigation of the accuracy of multi-input models using deep learning to estimate the tensile shear strength of adhesive joints

The correlation between the fracture surface images and residual tensile shear strength of adhesive joints immersed in water was investigated using deep learning. Multi-input models were used to investigate the effects of input parameters on the estimated strength. Specifically, the immersion time and temperature were added as inputs to the fracture surface image to identify the effects of multiple inputs and the conditions that contribute to the improved estimation accuracy. The estimation results showed that the highest accuracy was obtained when both immersion time and immersion temperature were added as input parameters. The variance in the estimated strength tends to be smaller for each additional parameter. To improve the accuracy of estimation using a multi-input model, approximate trends should be estimated for each input parameter alone. Conversely, the use of input parameters for which the trend cannot be estimated may reduce the estimation accuracy.

Enhancing Shear Strength in Hybrid Metal-Composite Single-Lap Joints Using Z-pins Fabricated via Fused Filament Fabrication

This paper investigates the interfacial shear strength of hybrid metal-composite single-lap joints (SLJs) reinforced with stainless steel Z-pins fabricated by fused filament fabrication (FFF). The joints were created by 3D printing an orthogonal array of 2 mm diameter steel Z-pins onto a steel substrate using FFF. The Z-pins were then embedded into a basalt fibre (BF)-fabric/epoxy resin composite using the Ultrasonically Assisted Z-FibreTM (UAZ) method to form a high-strength and tough interface. The results demonstrate that steel Z-pins produced via FFF effectively enhance the shear strength of the hybrid metal-composite SLJs, significantly improving joint performance. The study also explores the influence of Z-pin volume fraction and embedding height on SLJ shear strength. It was found that higher volume fractions and greater embedding heights of the Z-pins contribute to the increased shear strength. Compared to unreinforced joints, the maximum shear strength of the steel Z-pin reinforced joints increased by 120.1%. This enhancement is attributed to the effective energy absorption mechanisms, primarily facilitated by the frictional pull-out, plastic deformation and shear fracture of Z-pins accompanied by the formation of ductile dimples. These mechanisms suppress crack propagation and improve joint integrity. This study presents an innovative approach for fabricating hybrid metal-composite joints with enhanced toughness and strength.

Shear strength comparison of single lap and joggle lap adhesive joints in carbon fiber composites manufactured via vacuum-assisted resin infusion

The extensive utilization of composite materials has spurred the advancement of diverse joining techniques suitable for components constructed from such materials. This study focuses on the examination of two specific types of joints: single lap and joggle lap joints. The specimens utilized were composed of unidirectional carbon fiber composite combined with vinyl ester resin, manufactured via the vacuum-assisted resin infusion method. Vinyl ester adhesives were employed in the bonding process, with the joint surfaces undergoing sanding treatment prior to testing. Mechanical testing was conducted on the specimens according to ASTM D5868 standard, employing a constant crosshead speed until failure occurred. The test results reveal that the shear strength of single lap joints surpasses that of joggle lap joints. Within the single lap joint configuration, a mixed failure mode comprising both adhesive and cohesive failure is observed. Conversely, in joggle lap joints, substrate delamination is prevalent, suggesting the predominance of peel stress during loading.

Determining Rock Joint Peak Shear Strength Based on GA-BP Neural Network Method

The peak shear strength of a rock joint is an important indicator in rock engineering, such as mining and sloping. Therefore, direct shear tests were conducted using an RDS-200 rock direct shear apparatus, and the related data such as normal stress, roughness, size, normal loading rate, basic friction angle, and JCS were collected. A peak shear strength prediction model for rock joints was established, by which a predicted rock joint peak shear strength can be obtained by inputting the influencing factors. Firstly, the study used the correlation analysis method to find out the correlation coefficient between the above factors and rock joint peak shear strength to provide a reference for factor selection of the peak shear strength prediction model. Then, the JRC-JCS model and four established GA-BP neural network models were studied to identify the most valuable rock joint peak shear strength prediction method. The GA-BP neural network models used a genetic algorithm to optimize the BP neural network with different input factors to predict rock joint peak shear strength, after dividing the selected data into 80% training set and 20% test set. The results show that the error of the JRC-JCS model is a little bigger, with a value of 11.2%, while the errors of the established GA-BP neural network models are smaller than 6%, which indicates that the four established GA-BP neural network models can well fit the relationship between the peak shear strength and selected input factors. Additionally, increasing the factor number of the input layer can effectively improve the prediction accuracy of the GA-BP neural network models, and the prediction accuracy of the GA-BP neural network models will be higher if factors that have higher correlation with the output results are used as input factors.

Experimental study under thermal shock environment to investigate effect of welding width on properties of ultrasonically welded joints of multiple copper cables

Based on the ultrasonic welding technology, this study uses three different welding widths to weld copper cables with different specifications. The influence of welding width on the mechanical properties and microstructure of each group of welded joints was systematically studied for the first time. The thermal shock test was carried out for each group of welded joints under optimum welding width to simulate the influence of severe temperature change environment on joint performance. It is found that the cross-sectional area of joint is 20 mm2 and optimal welding width of joint composed of two and three cables is 7 mm. The optimal welding temperature of the joint composed of four cables is 5 mm. Under the optimal welding width, the average shear strength of two-cable joint reaches 309.4 N. The four-cable joint is only 232.2 N. Moreover, the welding strength weakens significantly as the number of cables and the peak temperature decreases. The high temperature of bonding interface is the key factor to form a good weld. The peak temperature during welding is negatively correlated with the porosity of joint and positively correlated with peeling strength of joint. In addition, the morphology of ultrasonically welded joints has changed obviously after thermal shock test. With the participation of oxygen, the surface of welded joint is gray and bright brass, while the interior of joint is purple due to lack of oxygen. Moreover, the phenomenon of atomic diffusion and thermal expansion generates joints which were initially in a mechanically interlocked form and welding interface of the metallurgical bond under the action of high temperature. So the maximum joint peel strength is slightly improved.

Mechanical performance of adhesive bonded joints with 1C-PUR adhesive at different angles

Reforestation trees are an alternative to meet industrial needs, and one potential application is their use in prefabricated structures, such as glued laminated timber (glulam). This study aimed to evaluate the shear strength of Pinus sp. bonded joints made using a single-component polyurethane adhesive (1C-PUR). The joints were produced varying the angles between the wood fibers ranging from 0º to 90º and were tested subjected to shear under compression load and to shear under torsional load. The use of the Hankinson’s equation as an estimator of shear strength of glued joints and the percentage of wood failure were also evaluated. A total of 144 specimens were tested. Half of the total was subjected to shear test under compression load while the other half was subjected to shear test under torsional load. The wood laminates used to make the joints were previously divided into eight groups according to their apparent density. The results showed that the shear strength was affected by the bonding angle, especially for those tested under compression loads. The mechanical behavior of the shear test under compression was considered different from that of the test under torsion for six of the nine angles used in the study. It was also found that Hankinson’s equation can be used as an estimate of the shear strength of joints bonded on different angles when the tests are performed under compression loads. However, the equation was not appropriate for estimating the test results when shear was caused by torsional loads. Overall, the bonded joints presented satisfactory shear strength and low percentage of wood failure. Furthermore, the results of this research were in accordance to those found on similar research where other adhesives were used.

Influence of hygrothermal aging on the lifetime and mechanical properties of GFRP/Al adhesive joints

The study aimed to investigate the impact of hygrothermal aging on the degradation of mechanical properties and predict the lifetime of adhesive joints between aluminum alloy (AA6061) and glass fiber-reinforced epoxy (GFRP) composites. The adhesive joints were prepared in a single lap joint (SLJ) configuration and subjected to hygrothermal conditions to induce aging. Immersion tests were conducted at a water temperature of 70°C with varying aging periods (10, 18, 40, 54, 60, and 75 days) to assess the long-term performance and predict the lifetime of the joints. The tensile and shear strength of the adhesive joints were evaluated using a tensile test. The test was performed at room temperature (RT) with a speed rate of 1.3 mm/min. Among the different methods available for lifetime prediction, a semi-empirical approach was selected to analyze the changes in the mechanical properties of the adhesive joints. A comprehensive comparison was made between aged and unaged specimens. The experimental results revealed a reduction in the ultimate tensile and shear strength of the adhesive bonds over the 75-day aging period. The semi-empirical relationship used for long-term durability prediction of adhesive joint structures indicated a 78% decrease in ultimate tensile strength for the adhesive joints over a one-year aging period. This highlights the significant influence of hygrothermal aging on the mechanical properties of the investigated adhesive joints. During the aged periods, various failure modes were observed, including adhesive failure, cohesive failure, and structural failure.

Polyvinyl acetate wood adhesive stabilized with hydroxyethyl cellulose: synthesis and characterizations

Specifically, the conventional wood adhesive uses polyvinyl alcohol (PVA) as colloid to stabilise the polyvinyl acetate (PVAc) emulsion. Green materials are being used as a result of recent study on chemicals and alternative sources. This factor has made the substitution of sustainable biopolymers for petrochemicals considerably more important. An emulsifier, sodium lauryl sulphate (SLS), was used during the addition polymerization process to produce a hydroxyethyl cellulose-grafted-poly (vinyl acetate) (HEC-g-P(VAc)) emulsion from HEC and VAc. The purpose of the study was to increase the content of renewable materials in the emulsion. The adhesive films glass transition temperatures (Tg) have been identified via Differential Scanning Calorimetry (DSC). The performance of the PVAc emulsion-based adhesive in accordance with EN 204 and EN 205 standards was evaluated by measuring the tensile shear strength of wood joints under both dry and wet conditions. The viscosity of the adhesives significantly increased along with the addition of HEC. The application of HEC led to an increase in PVAc film hardness, which was confirmed by the film’s glass transition temperature. In an environment that was wet, after 24 h, the tensile strength of the sample containing HEC increased by 54% compared to a pristine sample, as per EN 204 and EN 205. Water resistance significantly increased in sample with HEC, as was found by measuring the water contact angle which is in line with wet strength. The overall study conclusion emphasises the superior water resistance and increased adhesion capabilities of PVAc emulsion-based wood adhesives stabilised by HEC.

Mechanics guided data-driven model for seismic shear strength of exterior beam-column joints

This study presents an enhanced predictive model for the seismic shear strength of exterior beam-column joints (BCJs). Initially, the principles of strut-and-tie mechanism and variable selection procedures were first utilized to identify the most influential parameters. Subsequently, an evolutionary algorithm, specifically multigene genetic programming (MGGP), was utilized to search for the near-optimal predictive model. The dataset used to develop, train, and test the proposed model was compiled from previously published tests, focusing specifically on cyclically loaded exterior BCJs that encountered shear and flexure -shear failures. The prediction performance of the developed model was assessed through various statistical measures, and then compared with that of other existing models. Additionally, sensitivity analyses were also performed to identify the influence and importance of each design parameter. The results demonstrated that the methodology employed in this study yielded an elegant model that adheres to the underlying mechanics and provides higher prediction accuracy compared to existing models. Furthermore, the sensitivity analyses showed that BCJ shear strength positively correlates with concrete compressive strength, beam reinforcement, joint transverse reinforcement, column intermediate vertical reinforcement, and axial load ratio, while it negatively correlates with the joint aspect ratio. Among these design parameters, beam reinforcement has the greatest influence on the model response, followed by concrete compressive strength. Conversely, column intermediate vertical reinforcement and axial load ratio have the least impact on the model response. The notable prediction capabilities and robustness demonstrated by the developed model render it an efficient design tool with promising potentials for adoption by practicing engineers and for consideration in design guidelines.

Ultrasonic joining of carbon-reinforced polyamide with oak wood for manufacturing sustainable hybrid structures

The feasibility of manufacturing strong and lightweight hybrid joints of carbon fiber-reinforced polyamide (PA6-15CF) and oak wood using ultrasonic energy was successfully demonstrated. Before joining, a groove pattern was generated on the surface of the wood platelets by laser texturing. Wood platelets with and without texturing were joined with the polymer using the ultrasonic joining (U-Joining) process. Mechanical interlocking at the polymer-wood interface was improved, as the grooves and open vessels on the surface of the textured wood platelets were filled with the polymer composite. Therefore, the lap-shear strength of joints with textured wood was 9.2 ± 0.7 MPa, whereas the shear strength of joints with untextured wood was just 4.1 ± 0.8 MPa.

Study on microstructure and mechanical properties of vacuum brazing TC4 titanium alloy with Ti-37.5Zr-15Cu-10Ni amorphous filler metal

Ti-37.5Zr-15Cu-10Ni amorphous brazing filler metal was employed to join TC4 titanium alloy by vacuum brazing. This work investigated the effect of brazing temperature and holding time on the interfacial microstructure and mechanical properties of TC4/Ti-Zr-Cu-Ni/TC4 joints. Results indicate that the increasing brazing temperature above 900 ℃ and prolonging the holding time both promoted the formation of α-Ti + (Ti, Zr)2(Cu, Ni) eutectoid phases and acicular Widmanstätten. The shear strength of joints increased with elevating brazing temperature and the maximum value was 223.9 MPa obtained at 940 °C. When prolonging the holding time at the brazing temperature of 900 ℃, the shear strength increased firstly and then dropped. When the brazing temperature was 900 °C, the microhardness in the reaction layer was highest, reaching 572 HV0.1, which was caused by the formation of (Ti, Zr)2(Cu, Ni) intermetallic compounds. As the brazing temperature rose to 940 °C, the microhardness in the reaction layer decreased to 427.5 HV0.1.

Experimental study on shear mechanical properties of concrete joints under different unloading stress paths

In order to study the shear mechanical properties of rock joint under different unloading stress paths, the RDS-200 rock joint shear test system was used to carry out direct shear tests on concrete joint specimens with five different morphologies under the CNL path and different unloading stress paths. The unloading stress paths include unloading normal load and maintaining constant shear load (UNLCSL), unloading normal load and unloading shear load (UNLUSL), unloading normal load and increasing shear load (UNLISL). The results show that the peak shear strength, cohesion, internal friction angle, pre-peak shear stiffness and residual shear strength of concrete joints under CNL path increases with the increasing JRC and normal stress. Under the UNLCSL path, under the same initial shear stress τ1, instability normal stress σi decreases with the increasing JRC, and normal stress unloading amount Δσn increases with the increasing JRC. Under the same JRC, σi increases with the increase of τ1, and Δσn decreases with the increasing τ1. Under the same JRC and σi, τi is significantly smaller under the UNLCSL path than the CNL path. Under the same JRC, the cohesion under the UNLCSL path is less than the CNL path, and the internal friction angle is higher than that the CNL path. Under the same JRC and σi, τi is the largest under the path of CNL and UNLISL, followed by the UNLCSL path, and τi under the UNLUSL path is the smallest. Compared with the CNL path, the variation range of the specimen internal friction angle is within 3% while the average decrease percentage of the specimen cohesion reaches 37.6% under the UNLCSL path, UNLISL, and UNLUSL. Therefore, it can be inferred that the decrease in cohesion caused by normal unloading is the main reason for the decrease in joint instability shear strength. After introducing the correction coefficient k of cohesion to modify the Mohr-Coulomb criterion, the maximum average relative error after correction is only 3.5%, which is significantly improved compared with the maximum average relative error of 56.9% before correction. The research conclusions can provide some reference for the accurate estimation of shear bearing capacity of rock joints under different unloading stress paths, which is of great significance to the stability evaluation and disaster prevention of rock mass engineering.

The influence of false heartwood of European beech (Fagus sylvatica L.) on tensile shear strength of lap joints

The influence of false heartwood of European beech (Fagus sylvatica L.) on tensile shear strength of lap joints

Reaction mechanisms and mechanical properties of SiCf/SiC composite and GH536 superalloy joints using CoFeNiCrMn high-entropy alloy filler

To meet the service conditions and strength requirements of turbine stator blades and the inner and outer rings of aero engine casings, CoFeNiCrMn high-entropy alloy filler was used to braze SiCf/SiC/GH536 joints. This study investigated the effects of holding time on the joints' microstructure and mechanical properties. Key phases identified in the welded joints include MoNiSi, FCC, and Cr23C6 near the composites, with brittle Ni3Si and Fe2Si intermetallic compounds forming due to filler diffusion. Optimal brazing parameters were found to be 1220 °C for 30 min with a shear strength of 64.28 MPa. The study also highlighted that increased holding time at the same temperature enhances diffusion at the joint, increasing brittle intermetallic compounds, initially improving shear strength, which then declines. Microstructural and fracture morphology analyses revealed that insufficient insulation time leads to poor welding and stress concentration at pores, causing cracks. Excessive insulation time results in joint fractures due to the brittleness of Ni3Si and Fe2Si intermetallic. Thus, joint shear strength correlates with welding quality and intermetallic compound distribution.

Seismic performance of new detailing RCS connection with different axial compression ratio and FBP thickness

Reinforced Concrete column and Steel beam (RCS) structural system has been extensively studied due to the effective use of concrete and steel material and cost efficiency. Bearing failure and constructability were two main issues of RCS joint in practical engineering. To improve these two deficiencies, the authors proposed a whole-section diaphragm type RCS joint. This study aimed to examine the impact of axial compression ratio and face bearing plate (FBP) thickness on the seismic behavior of the proposed joint. In this research, six RCS joint specimens were designed to achieve joint failure and tested under cyclic loading. Shear failure was identified as the typical failure mode. The results revealed that higher axial, compression ratio could lead to higher cracking loads, with improved load-carrying capacity, stiffness, and energy dissipation capabilities. Additionally, the joint bearing distortion reduced as the axial compression ratio increased. All specimens displayed spindle-shaped hysteresis loops while the specimen without axial compression exhibited pinching effect. The presence of parallel FBPs significantly improved the shear capacity. However, as the thickness of the parallel FBPs increased from 6 mm to 10 mm, the load-carrying capacity showed limited enhancement. Moreover, a comparative analysis of current calculation methods was conducted. The results demonstrated that the AIJ and CECS347:2013 formulas showed acceptable accuracy in predicting the joint shear strength. These findings validated the applicability of the existing methods for proposed composite joints, while the effect of the axial compression ratio required further evaluation.

Regression prediction model for shear strength of cold joint in concrete

The shear resistance of cold joint in concrete is influenced by various design parameters. Traditional mechanical models typically consider only a limited number of parameters to predict the shear strength of cold joints. This research aims to explore the complex nonlinear relationship between design parameters and cold joint shear strength using statistical method and machine learning technology. The goal is to develop a more accurate, reliable, and engineering applicable regression model for predicting shear strength. A dataset of 546 Z-shaped shear specimens characterizing cold joint in concrete was constructed, involving a total of 16 variables that may affect shear performance. Correlation analysis and recursive elimination were adopted to eliminate correlated and insignificant variables based on their importance. Multiple linear regression (MLR), random forest regression (RFR), and support vector machine regression (SVR) prediction models for cold joint shear strength were established based on rigorously screened variables and comprehensively evaluated using multiple methods. It was found that the most significant factors influencing the shear strength of cold joints are concrete strength, interface shear key, product of interface reinforcement strength and its reinforcement ratio, normal stress, fiber length of new concrete, casting method of the new concrete, and product of the fiber length and its tensile strength of old concrete. The MLR, SVR, and RFR models all exhibited superior performance relative to traditional mechanics-based models with regard to shear strength prediction of cold joints. The RFR model is recommended for predicting the shear strength of cold joints due to its superior evaluation indexes in comparison to the MLR and SVR models, and variable sensitivity analysis shows that it does not yield common-sense errors.

Effect of Feed Rate on Shear Strength and Macrostructure of Friction Stir Welding Dissimilar High Density Polyethylene-Polypropylene Joint

The connection of dissimilar materials is complicated, too. This connection is due to differences in physical and mechanical properties, but with the development of technology, dissimilar materials can be joined using solid-state welding methods. Dissimilar joints can produce a good combination of structure and mechanical properties. One of them is friction stir welding, which is used to connect sheet materials. The welding process of this research uses a conventional vertical milling machine. This study aims to determine the maximum shear strength and welding defects against variations in the feed rate of lap joints dissimilar high-density polyethylene with polypropylene. The machining parameters used in this experiment were 4 mm pin tool diameter, 2360 rpm rotation speed, 9 mm/min, 12 mm/min, and 16 mm/min feed rate. The results showed that the highest shear strength was obtained using the 12 mm/min feed rate variation of 3.11 N/mm. It can be seen in the macrostructure that the incomplete defects produced are less than the other welding process variations.

Effects of Minor Zn Dopants in Sn-10Bi Solder on Interfacial Reaction and Shear Properties of Solder on Ni/Au Surface Finish.

Sn-10Bi low-bismuth-content solder alloy provides a potential alternative to the currently used Sn-Ag-Cu series due to its lower cost, excellent ductility, and strengthening resulting from the Bi solid solution and precipitation. This study primarily investigates the interfacial evolution and shear strength characteristics of Sn-10Bi joints on a Ni/Au surface finish during the as-soldered and subsequent isothermal aging processes. To improve the joint performance, a 0.2 or 0.5 wt.% dopant of Zn was incorporated into Sn-10Bi solder. The findings demonstrated that a 0.2 or 0.5 wt.% Zn dopant altered the composition of the intermetallic compound (IMC) formed at the interface between the solder and Ni/Au surface finish from Ni3Sn4 to Ni3(Sn, Zn)4. The occurrence of this transformation is attributed to the diffusion of Zn atoms into the Ni3Sn4 lattice, resulting in the substitution of a portion of the Sn atoms by Zn atoms, thereby forming the Ni3(Sn, Zn)4 IMC during the soldering process, which was also verified by calculations based on first principles. Furthermore, a 0.2 or 0.5 wt.% Zn dopant in Sn-10Bi significantly inhibited the Ni3(Sn, Zn)4 growth after both the soldering and thermal aging processes. Zn addition can enhance the shear strength of solder joints irrespective of the as-soldered or aging condition. The fracture mode was determined by the aging durations-with the brittle mode occurring for as-soldered joints, the ductile mode occurring for aged joints after 10 days, and again the brittle mode for joints after 40 days of aging.