Pullout Failure Mode Research Articles

Failure Study of Two Dissimilar Steels Joined by Spot Welding Technique

Resistance spot welding (RSW) process is of paramount importance in automotive industry for the fabrication of metallic components. Several dissimilar alloys could easily be joined by resistance spot welding. However, the joining of the stainless steel and galvanized carbon steel is challenging task since weld fusion zone properties are affected significantly. Indeed, the reliability of the component lies in the sound quality of spot weld. The overload failure mode of the weld zone was determined by preparing lap-shear specimens and then carrying out tensile-shear test. Microstructures and hardness of the weld nuggets were also brought under considerations. It was found that weld nugget size and strength of that sheet material which has lower electrical resistance are the controlling factors of the failure mode. The aim of this study was to find out the causes of spot welds failure in terms of parameters favoring the pull-out failure mode, role of fusion zone size (FZS), nugget and base metal by controlling the process parameters.

Bond strength of reinforcing bars considering failure mechanism

Abstract Because the bond strength between a reinforcement and concrete is affected by various factors, including the compressive strength of the concrete, concrete cover thickness and reinforcement geometry, the bond mechanism is very complicated. This study proposed an analytical model that estimates the bond strength of the steel reinforcement considering both the splitting and pullout failure modes based on mathematical modeling of the stress field in reinforcement and the surrounding concrete. The results of the comparison between the analytical results obtained by the proposed model and test results reported in the literature showed that the proposed model can adequately estimate the bond failure mode and bond strength of the collected test specimens.

Weld bonding process analysis for tensile shear strength and peel strength of weld bonded joints of dissimilar steel sheets

Evaluating the strength performance of resistance spot welded joints in dissimilar material is critical for their continued integration into the automobile and aerospace industries. The effect of joint strength is an important consideration in the design of welded structures. The aim of this paper is to evaluate the effect of the welding process parameters (welding current, weld time, and electrode pressure) on the mechanical performance of dissimilar weld bonds between austenitic stainless steel 304L and low carbon steel sheets. Mechanical properties of weld bonds are described in terms of bond strength, failure mode, and hardness of the joint. Weld bonding experiments were planned on the basis of full factorial design matrix. Weld bonded joint strength tests showed that the maximum tensile shear strength and peel strength were achieved at 6.4 kA, eight-cycle weld time with 3 kg/cm2 electrode pressure. The hardness value across the weld bonded fusion zone was not affected much with respect to varying the welding current. Pullout failure and tearing failure modes were observed during the tensile shear strength test of weld bonded joints. Application of adhesive layer at faying surfaces resulted not only in strengthening but also distributing the stress in weld bonded joints.

Microstructure and Mechanical Properties of Resistance Spot Welds for Fe-based Metallic Glass

The lap joints of Fe-based metallic glass ribbons were carried by resistance spot welding, and the microstructures of spot welds were investigated by X-ray diffraction and transmission electron microscopy. The results indicated that the perfect formations of joints without typical defects such as spatter were achieved with optimized parameters. Except for little nano-particle Fe2B, no other crystalline particle was detected by TEM, revealing that the most microstructure in spot weld remains amorphous. The maximum tensile-shearing force was 45.0 N with the optimized parameters of 1 kA weld current, 30 N electrode force and 0.02 ms weld time. The spot weld failed as pullout failure mode propagating along the interface of nugget zone. The study demonstrates that resistance spot welding is an effective and practical welding process for Fe-based metallic glass.

Effect of weld nugget size on failure mode and mechanical properties of microscale resistance spot welds on Ti–1Al–1Mn ultrathin foils

We use tensile–shear tests to investigate the failure modes of Ti–1Al–1Mn microscale resistance spot welds and to determine how the failure mode affects the microstructure, microhardness profile, and mechanical performance. Two different failure modes were revealed: interfacial failure mode and pullout failure mode. The welds that fail by pullout failure mode have much better mechanical properties than those that fail by interfacial failure mode. The results show that weld nugget size is also a principal factor that determines the failure mode of microscale resistance spot welds. A minimum weld nugget size exists above which all specimens fail by pullout failure mode. However, the critical weld nugget sizes calculated using the existing recommendations are not consistent with the present experimental results. We propose instead a modified model based on distortion energy theory to ensure pullout failure. Calculating the critical weld nugget size using this model provides results that are consistent with the experimental data to high accuracy.

Resistance spot welding of MS1200 martensitic advanced high strength steel: Microstructure-properties relationship

This paper addresses the microstructure and tensile-shear mechanical performance of MS1200 Giga-grade martensitic advanced high strength steel resistance spot welds. The key phase transformations in MS1200 welds were lath martensite formation in the fusion zone (FZ) and upper-critical heat affected zone (HAZ), new ferrite formation in the inter-critical HAZ and martensite tempering in the sub-critical HAZ. The MS1200 welds were featured by a near matching hardness in the fusion zone and under-matching hardness in the heat affected zone (HAZ) compared to the base metal. At certain process window a complete nugget pullout and separation was observed with high post-necking tearing energy. The interfacial to pullout failure mode transition was explained in the light of FZ hardness as well as the HAZ softening associated with martensite tempering in the sub-critical HAZ. The load bearing capacity of MS1200 welds failed at interfacial mode was strongly depends on the FZ size as well as the FZ hardness. However, the peak load of welds failed at pullout mode was a function of HAZ softening as well as the plastic constraint in the HAZ associated with the hard upper-critical HAZ/FZ and martensitic BM.

In situ postweld heat treatment of transformation induced plasticity steel resistance spot welds

ABSTRACTTransformation-induced plasticity (TRIP) steel resistance spot welds are delicate to low-energy interfacial failure via crack propagation through martensitic fusion zone during cross-tension (CT) loading. This paper addresses the effect of three different types of in situ postweld heat treatment (PWHT) on the mechanical properties of TRIP steel resistance spot welds. Depending on the post weld second pulse current level, three different strengthening mechanisms were found including (i) martensite tempering with reduced hardness, (ii) refining of martensite packets with improved toughness and (iii) nugget re-melting/enlargement combined with possible reduction of grain boundary impurity segregation. All designed in situ PWHTs were enabled to promote pullout failure mode with improved load-bearing capacity and energy absorption capability during CT loading.

Fixation Strength of Polyetheretherketone Sheath-and-Bullet Device for Soft Tissue Repair in the Foot and Ankle

Tendon transfers are often performed in the foot and ankle. Recently, interference screws have been a popular choice owing to their ease of use and fixation strength. Considering the benefits, one disadvantage of such devices is laceration of the soft tissues by the implant threads during placement that potentially weaken the structural integrity of the grafts. A shape memory polyetheretherketone bullet-in-sheath tenodesis device uses circumferential compression, eliminating potential damage from thread rotation and maintaining the soft tissue orientation of the graft. The aim of this study was to determine the pullout strength and failure mode for this device in both a synthetic bone analogue and porcine bone models. Thirteen mature bovine extensor tendons were secured into ten 4.0 × 4.0 × 4.0-cm cubes of 15-pound per cubic foot solid rigid polyurethane foam bone analogue models or 3 porcine femoral condyles using the 5 × 20-mm polyetheretherketone soft tissue anchor. The bullet-in-sheath device demonstrated a mean pullout of 280.84 N in the bone analog models and 419.47 N in the porcine bone models. (p = .001). The bullet-in-sheath design preserved the integrity of the tendon graft, and none of the implants dislodged from their original position.

Characteristics of Resistance Spot Welded Ti6Al4V Titanium Alloy Sheets

Ti6Al4V titanium alloy is applied extensively in the aviation, aerospace, jet engine, and marine industries owing to its strength-to-weight ratio, excellent high-temperature properties and corrosion resistance. In order to extend the application range, investigations on welding characteristics of Ti6Al4V alloy using more welding methods are required. In the present study, Ti6Al4V alloy sheets were joined using resistance spot welding, and the weld nugget formation, mechanical properties (including tensile strength and hardness), and microstructure features of the resistance spot-welded joints were analyzed and evaluated. The visible indentations on the weld nugget surfaces caused by the electrode force and the surface expulsion were severe due to the high welding current. The weld nugget width at the sheets’ faying surface was mainly affected by the welding current and welding time, and the welded joint height at weld nugget center was chiefly associated with electrode force. The maximum tensile load of welded joint was up to 14.3 kN in the pullout failure mode. The hardness of the weld nugget was the highest because of the coarse acicular α′ structure, and the hardness of the heat-affected zone increased in comparison to the base metal due to the transformation of the β phase to some fine acicular α′ phase.

Analysis of the stiffness and load-bearing capacity of glued laminated timber beams reinforced with strands

In this paper a benefit of glulam pinewood beams reinforced strands is discussed. In the first phase, series of pull-out tests were performed on specimens made up of different types of glue (melamine-urea-formaldehyde, epoxy and others) to detect pull-out force and failure mode of a specimens. In the second phase, series of equal cross-section glulam beams with strand and rod reinforcement were theoretically analysed using transformed cross-section method. Additionally, series of experimental testing were made. Benefits of strand reinforcement use as glulam beams’ reinforcement were identified and examined the possibility of one glue type application in all operations of reinforced glulam beams manufacturing.

Resistance spot welding of martensitic stainless steel: Effect of initial base metal microstructure on weld microstructure and mechanical performance

This paper addresses the microstructure-properties relationship during resistance spot welding of martensitic stainless steel (MSS). The effect of the initial base metal microstructure (ferritic microstructure in annealed condition vs. partially tempered martensitic in quench and tempered condition) on the weld microstructure evolution is highlighted. Regardless of the initial base metal microstructure, the fusion zone exhibited a predominantly martensitic structure plus some δ-ferrite. The heat affected zone (HAZ) in the quenched and partially tempered (Q-PT) sheet was featured by formation of martensite and carbide in upper-critical zone and tempering of martensite in sub-critical zone. The latter caused pronounced softening in the HAZ compared to the base metal. However, the HAZ in the annealed sheet exhibited hardening compared to the base metal due to the formation of a dual phase microstructure composed of martensite plus carbide. Nor high strength mismatch between fusion zone and base metal (when welding in the annealed condition), neither severe HAZ softening (when welding in the Q-PT condition) did not promote pullout failure mode. The consistently predominant interfacial failure of the MSS welds was governed by the low fracture toughness of the fusion zone.

Resistance spot welding of dissimilar austenitic/duplex stainless steels: Microstructural evolution and failure mode analysis

The paper addresses the microstructural evolution and failure mode analysis for dissimilar resistance spot welding of austenitic and duplex stainless steels. Microstructural examination by optical and scanning electron microscopes revealed that pre-existing TiC particles in the base metal microstructure of the duplex stainless steel were responsible for changing the nature of solid state phase transformations in heat affected zone and columnar to equiaxed transition grain structure in fusion zone due to heterogeneous nucleation. Moreover, it was found that simultaneous occurrence of constitutional liquation of these TiC particles as well as grain boundary sweeping mechanisms led to grain boundary liquation in the heat affected zone of the investigated duplex stainless steel. Failure analysis after the tensile-shear testing revealed that in the partial thickness-partial pullout failure mode fracture initiates in a similar manner as pullout failure mode; and it was found that the work hardening ability of the parent metals is the key controlling factor for crack initiation site.

Experimental Study on Bond Characteristics of Adhering Sand and Ribbed Surface FRP Bars with Concrete

The mechanical performance of fiber reinforced polymer (FRP) reinforced concrete structure is directly affected by the bond behavior between concrete and FRP bars, which is obviously different from steel bars. The bond characteristics of adhering sand and ribbed surface FRP bars (ASRSFBs) and plain FRP bars were investigated in pullout tests and compared to that of ribbed steel bars and plain steel bars, respectively. Results of the tests indicated that ASRSFBs showed good bond capacity with concrete and the bond strength and slip values of the profiled FRP bars were a little lower than that of ribbed steel bars, while the plain FRP bars were proved to be unable to serve as reinforcement owing to far lower bond strength than that of plain steel bars. Moreover, the specimens reinforced with ASRSFBs exhibited a pull-out failure mode, and the adhering sand on the surface of FRP bars were ground into powder-like. Shear slip was found between ribbed protrusion and core fiber of FRP bars, causing longitudinal shear-bond failure. It was concluded that the bond strength was controlled by the type of resin.

Pull-out behavior of straight steel fibers from asphalt binder

The interaction between a straight steel fiber and the surrounding asphalt matrix is investigated through single fiber pull-out tests and numerical simulations. Based on experimental observations from 240 pull-out tests for various temperatures, displacement rates, and fiber dimensions, pull-out failure modes are classified into three types: matrix, interface, and mixed failure modes. The experimental data suggests that there is a critical shear stress beyond which fiber-binder interface debonding will occur. Detailed finite element analyses employing a nonlinear viscoelastic constitutive model for asphalt are carried out to explain the observed test results. The numerical simulations show that the stress distribution along the fiber surface varies substantially with temperature and fiber dimensions. At −20°C, the concentration of interfacial shear stress becomes significant as the embedded aspect ratio of fibers becomes higher, and causes a decrease in the value of average interfacial shear stress at the onset of the interface debonding. The simulations also showed that this stress concentration decreases at 0°C as the contribution of viscous behavior becomes more significant. The simulation results confirm that the shear bond strength between steel fiber and asphalt binder is 6.9MPa, and it is independent of temperature, loading rate, and fiber dimensions within the ranges used in the study.

Simulation analysis of large-diameter post-installed anchors in concrete

Large-diameter anchors are one of the important connection components in the reinforcement of industrial facilities. In the present study, a finite element (FE) model of large-diameter post-installed anchor system is appropriately established to investigate its pull-out performance and failure modes observed in the prototype experiments. The applicability of the proposed model is discussed through comparison of its results with experimental results (e.g., in terms of the ultimate load, corresponding displacement, and failure modes), and the parametric sensitivity based on the numerical results is studied. The results showed that the pull-out behavior could be well simulated using the proposed model. The progressive failure evolution process of the large-diameter anchor can be revealed by computational load–displacement curves. Thus, the proposed model of a large-diameter post-installed anchor can enable reliable design of anchor systems for industrial reinforcements.

Effect of embedment length on pullout behavior of amorphous steel fiber in Portland cement composites

For using amorphous steel fibers (ASF) in Portland cement composites, the performance of ASF was evaluated by a pullout test and compared to that of a hooked-end steel fiber (HSF). The embedment length of the fiber (5.0, 8.0, and 12.5mm), compressive strength of the mortar, and number of fibers were considered the test variables. The results showed that a single ASF had a greater maximum applied load (Pmax) than a single HSF; however, at a mortar compressive strength of 30–42MPa, its bond strength (τmax) and pullout energy (Ef) decreased by 40.9–55.8% and 16.9–79.7%, respectively, compared to those of a single HSF. Furthermore, in the pullout failure mode, the Ef of 4 ASFs, which have a volume fraction equivalent to a single HSF, was 2.10–3.04 times higher than that of a single HSF. Based on the Ef of ASFs, an embedment length of 5–8mm is recommended to provide the most effective ASF reinforcement effect to a mortar with a compressive strength of up to 40MPa.

Failure modes of spot welds in quasi – static tensile – shear loading of coated steel sheets.

Failure modes of resistance spot welds of steel sheet largely depends upon the complex interplay between the weld geometry, fusion zone and heat affected zone. Steel sheet are potential material for automobile industry and aerospace. The present article investigates the mode of failure of resistance spot welded joints of 0.8 mm thickness sheet by tensile observed. There is critical fusion size to ensure nugget pullout failure mode in tensile- shear test. Scanning electron microscope (SEM) images shows that the failure mode are partially pullout and partially interfacial.

All-Suture Anchors: Biomechanical Analysis of Pullout Strength, Displacement, and Failure Mode

To evaluate the biomechanical and design characteristics of all-suture anchors. All-suture anchors were tested in fresh porcine cortical bone and biphasic polyurethane foam blocks by cyclic loading (10-100N for 200 cycles), followed by destructive testing parallel to the insertion axis at 12.5mm/s. Endpoints included ultimate failure load, displacement at 100 and 200 cycles, stiffness, and failure mode. Anchors tested included JuggerKnot (1.4, 1.5, and 2.8), Iconix (1, 2, and 3), Y-knot (1.3, 1.8, and 2.8), Q-Fix (1.8 and 2.8), and Draw Tight (1.8 and 3.2). The mean ultimate failure strength of the triple-loaded anchors (564 ± 42N) was significantly greater than the mean ultimate failure strength of the double-loaded anchors (465 ± 33N)(P= .017), and the double-loaded anchors were stronger than the single-loaded anchors (256 ± 35N)(P < .0001). No difference was found between the results in porcine bone and biphasic polyurethane foam. None of these anchors demonstrated 5mm or 10mm of displacement during cyclic loading. The Y-Knot demonstrated greater displacement than the JuggerKnot and Q-Fix (P= .025) but not the Iconix and Draw Tight (P > .05). The most common failure mode varied and was suture breaking for the Q-Fix (97%), JuggerKnot (81%), and Iconix anchors (58%), anchor pullout with the Draw Tight (76%), whereas the Y-Knot was 50% suture breaking and 50% anchor pullout. The ultimate failure load of an all-suture anchor is correlated directly with its number of sutures. With cyclic loading, the Y-Knot demonstrated greater displacement than the JuggerKnot and Q-Fix but not the Iconix and Draw Tight. JuggerKnot (81%) and Q-Fix (97%) anchors failed by suture breaking, whereas the Draw Tight anchor failed by anchor pullout (76%). All-suture anchors vary in strength and performance, and these factors may influence clinical success. Biphasic polyurethane foam is a validated model for suture anchor testing.

Microstructure and Tensile-Shear Properties of Resistance Spot Welded 22MnMoB Hot-Stamping Annealed Steel

The present paper deals with the joining of 22MnMoB hot-stamping annealed steel carried out by the spot welding process. Microstructural characterization, microhardness testing and tensile-shear testing were conducted. The effects of the welding parameters, including the electrode tip diameter, welding current, welding time and electrode force upon the tensile-shear properties of the welded joints, were investigated. The results showed that a weld size of 9.6 mm was required to ensure pullout failure for the 1.8-mm-thick hot-stamping annealed steel sheet. The welding current had the largest influence upon the tensile-shear properties of the 22MnMoB steel welded joint. The bulk resistance should play an important role in the nugget formation. In pullout failure mode, failure was initiated at the heat-affected zone, where softening occurs owing to the tempering of martensite.

Fracture toughness of martensitic stainless steel resistance spot welds

The paper is focused on the strength and fracture toughness of AISI420 martensitic stainless steel resistance spot welds under the tensile-shear loading. The failure behavior of AISI420 spot welds was featured by quasi-cleavage interfacial failure with low load bearing capacity and weak energy absorption capability which was a function of the weld fusion microstructure, predominately carbon and chromium rich martensite plus δ-ferrite. Fracture toughness of the fusion zone proved to be the most important factor controlling the peak load of the spot welds made on AISI420 failed in interfacial mode. A geometry-independent fracture toughness of the weld nugget (c.a. 23 MPam0.5) was determined using fracture mechanics concept. Through modeling it was found that there is a critical fracture toughness which beyond that the pullout failure mode can be obtained which is a function of sheet thickness and tensile strength of the base metal.