Pullout Failure Mode Research Articles

Experimental investigation on the dynamic behavior of grouted splice sleeve connector under fast tensile loading

This paper presents an experimental program designed to investigate strain rate effects on the bond behavior of grouted splice sleeves connected with deformed steel bars. Thirty-six grouted splice sleeve specimens with different anchorage lengths were designed and tested under direct dynamic tensile loads with four loading strain rates (10−3, 10−1, 10° and 10+1 s−1). Strain gauges were employed to record the strain of the sleeve and rebar. The failure modes and the dynamic bond-slip relationships of specimens were obtained. The results show that the bond force capacity increases with an increase in the strain rate. However, the failure mode shifts from the steel bar fracture towards steel bar pullout as the strain rate increases. The mechanisms of a dynamic load transmission are described based on the experimental results. A dynamic analytical procedure incorporating the strain rate effects was developed to predict the bond force-slip relationships and was validated by comparing the experimental bond force-slip curves. The shifting of failure modes was attributed to the damage aggravation effects of the grouted mortar, which led to a reduced effective anchorage length and a steel bar pullout failure mode at high strain rates. In addition, based on the proposed analytical model, the required anchorage length of grouted splice sleeves at different strain rates was calculated and an empirical model was developed to determine the critical embedment length to facilitate engineering design.

Weldability study of dual phase and transformation induced plasticity automotive steels

Resistance spot welding studies at varying current with an 8 mm electrode on steel grades DP980, DP690, TRIP980 and TRIP780, established that peak strength with sound weld could be achieved at a current range of 9 to 10 kA, where the nugget diameter was between 6.9 and 7.5 mm. The joint efficiency, measured as hardening ratio was highest in TRIP690 at 2.22 and for higher strength grade it was between 1.37 to 1.51. The softening ratio in the HAZ associated with tempering of preexisting martensite, was 0.86 to 0.9. Higher fusion strength was associated with alloying content that increased resistance that increased weld pool fusion that enhanced the nugget diameter and hence the strength. The TRIP steel at high cooling rate showed martensite and retained austenite and the DP steel showed martensite content in higher grade and dispersed ferrite with martensite in the lower DP grade. The Tensile shear strength was lowest (16kN) for DP780, while for other grades it is between 20 to 22 kN. The strength enhancement in TRIP steel was due to higher weld diameter at higher current, where partial pull out failure mode was observed. At lower current, the interfacial pull out failure mode was observed with poor fusion and at high currents partial pull out at HAZ is observed. The Coach peel strength was highest at 3.2 kN for DP780, 2.2 kN for DP980, 2 kN for TRIP 690 and 1.7kN for TRIP 980 and follows the trend in TSS. The observed failure may be attributed to the high fusion strength in TRIP steel due to sound nugget and a microstructure of martensite with retained austenite. The lower strength with DP steels is attributed to low alloyed lath martensite in DP 980 and the lower grade DP780 is softer associated with ferrite dispersion in martensite. At very high currents, the fusion is good but there is pull out at HAZ due to the softening associated with the tempering of preexisting martensite that influenced the failure at HAZ failure mode.

AISI 2205 DSS for body-in-white automotive structure: effect of welding current and time on the performance of spot welded joint

Duplex stainless steel is an ideal candidate in the automotive sector leading to a significant weight reduction and enhancement in product safety. In the present work, two major influencing process parameters i.e. welding current and welding time have been considered to investigate the mechanical and metallurgical performance of resistance spot welded duplex stainless steel. Other important process parameters, such as electrode force, squeeze time and hold time have been kept constant throughout the process. Results show that tensile shear strength (TSS) increases with an increase in welding current as well as welding time due to more amount of heat generation at interface. However, excessive value of both results in the expulsion of weld material which significantly alters the nugget diameter and cause decrease in TSS. Moreover, the failure mode is changed from interfacial failure (IF) mode to pull-out failure (PF) mode at the higher value of welding current and time. Microstructural observation reveals that the fusion zone (FZ) is consisted of columnar grain structure, whereas heat affected zone (HAZ) contains equiaxed grain structure. Furthermore, the phase balance of austenite and ferrite is completely disturbed in the FZ and HAZ.

Numerical study on the stiffness and ultimate strength of cold-formed steel C-shaped connectors under pull-out failure

ABSTRACT In this paper, cold-formed steel C-shaped connectors, as one of the most commonly used components in steel wall/framing systems, were investigated under the pull-out failure modes using a detailed numerical study. Finite element models were validated using the data obtained from an experimental program; and the results were compared with the current design equations. Finally, a new pull-out strength equation was proposed based on the critical parameters affecting the behaviour of C-shaped connectors. In addition, initial bending stiffness of C-shaped connectors was studied using a simplified analytical approach; and the results obtained from the proposed new stiffness equation were compared with the initial slope of experimental and numerical force-displacement curves. These comparisons confirm the accuracy of the new strength and stiffness equations in order to apply to the analytical methods such as component-based method in future works.

Anchorage behavior of Fe-SMA rebars Post-Installed into concrete

The unique self-prestressing behavior exhibited by Iron-based shape memory alloys (Fe-SMAs) coupled with the ease of application makes them suitable for numerous structural applications requiring post-installed reinforcement. However, the practical realization of Fe-SMA rebars as post-installed reinforcement systems entails an understanding of their bond behavior with concrete to ensure the use of adequate anchorage length for prestress transfer and prevention of premature failure. The bond behavior of cast-in-place and near-surface mounted Fe-SMA rebars with concrete has been investigated in detail in a few recent studies. However, no study has so far investigated the bond behavior of Fe-SMA rebars post-installed into concrete. To address this important knowledge gap, this paper presents an extensive experimental campaign aimed at evaluating the anchorage of post-installed Fe-SMA rebars in concrete. The experimental campaign comprised 23 specimens, with the variable parameters of the study including the bond length, state of Fe-SMA rebar (non-activated or activated), drill-hole size, strength of the adjacent concrete, type of rebar (plain, threaded, or deformed), and the type of loading history (monotonic or cyclic). The experimental results showed that for bond lengths ≥ 5db, the ribbed Fe-SMA rebars primarily fail in a pull-out failure mode and exhibit large inelastic rebar strains and load capacity at bond failure. The paper is concluded with the comparison of anchorage length predictions of conventional design models with the results of the current experimental testing campaign. The comparison demonstrates that the anchorage length recommendations of existing design standards are generally conservative for Fe-SMA rebars.

Modelling root–soil mechanical interaction considering root pull-out and breakage failure modes

Modelling root–soil mechanical interaction considering root pull-out and breakage failure modes

Resistance spot welding of NiTi shape memory alloy sheets: Microstructural evolution and mechanical properties

Resistance spot welding was used for welding superelastic NiTi shape memory alloy sheets. The microstructure of the welded sample showed a fully austenitic NiTi nugget without any visible weld defect due to the insignificant change in the transformation temperature during the welding process. Additionally, the fusion zone has a homogenous microhardness distribution with an average hardness value of ~340 HV, which is below the average hardness value for NiTi base material (~410 HV) because of the large grain size in the weld nugget. The perseverance of the superelastic response as a main functional property of NiTi alloy after the RSW procedure is significant. The welded sample failed via pullout failure mode during tensile shear loading conditions. Face digital image correlation imaging confirmed that strain is localized in the area around the nugget. The dominant fracture mode of the sample during tension-shear loading was ductile, and the EBSD results of the fracture area revealed the excessive deformation around the HAZ resulted in a transgranular fracture. Therefore, resistance spot welding is highly capable of providing a sound, straightforward and reliable joint between NiTi sheets.

Experimental evaluation of the bond Between concrete and GFRP bars with different surface treatments

The bond between glass fiber-reinforced polymers (GFRPs) and steel reinforcements to concrete is investigated in this study. The experimental program includes two different testing methods (beam tests and pull-out tests) on three different types of reinforcement with various materials, diameters, and surface treatments. For each type of reinforcement rebar and test method, three specimens were tested. A total of 12 beam tests and 12 pull-out tests were performed to analyze the effect of a bar´s diameter, the type of surface treatment, and the configuration of the test on the bond strength of the bar to the concrete. All but one of the bars investigated failed in the pull-out failure mode and showed good bonding behavior to the concrete. The results of the experimental investigation indicate that an increase in the diameter of GFRP bars causes a decrease in the bond stress when a beam bond test is performed and that the surface treatment of GFRP bars has a significant effect on the bond mechanism. Similar bond-slip behavior was observed in both testing methods.

Upper Bound Finite Element Limit Analysis of Pullout Characteristics of Normal-Stressed Circular Anchor Plate

In this paper, the pullout factor and failure mode of circular anchor plate at an inclined angle with the horizontal ground under the normal stress are studied with the method of the upper bound finite element limit analysis. The effects of soil cohesion, internal friction angle, anchor plate inclination angle, and embedded ratio on the pullout factor are investigated to reveal the evolution of fracture surface of the soil around anchor plate under limit state. It is noted that the analysis of variance is adopted to process a series of data related to pullout capacity for obtaining the expression of the anchor plate’s pullout factor. The results show that the internal friction angle is the key factor determining the pullout characteristics of the anchor plate. Particularly, the effect of the inclination angle on pullout capacity is highly correlated to the internal friction angle. For φ = 0 ° , failure zone around anchor plate is presented as localization plastic zone and pullout capacity is linearly related to soil cohesion. The effect of inclination angle on pullout resistance is less significant. For φ ≠ 0 ° , the failure mode around the anchor plate is developing into full failure zone extending from both sides of anchor plate to ground. It is clearly noted that angle between the failure surface and horizontal line is greatly affected by the inclination of the anchor plate. Moreover, the effect of the inclination angle on pullout factor increases with increasing internal friction angle, which should be considered in the evaluation of the pullout bearing characteristics of the inclined circular anchor plate.

Tensile and Pull-Out Behavior of Steel Reinforced Grout Connectors

Mortar-based composites are an emerging technology for the repair and strengthening of reinforced concrete and masonry structures. In most cases, the effectiveness of the retrofitting work relies on the substrate-to-composite bond capacity but in some applications, connectors are also used to prevent debonding and improve the performance of the retrofitted structure. Indeed, the use of connectors is recommended by design guidelines and suppliers are required to test them for acceptance. The paper presents a laboratory investigation on steel reinforced grout connectors, made by rolling ultra-high tensile strength steel textiles, comprising either galvanized or stainless-steel micro cords. Tensile tests were first carried out for mechanical characterization. Pull-out tests were then performed on connectors installed in holes drilled in wall panels and injected with either cement or lime mortars. Concrete, tuff masonry, brickwork and limestone masonry were used as substrate materials. Test results are commented to analyze the effect of textile rolling on tensile response, of textile and matrix properties on pull-out strength and failure mode, as well as to highlight their significance for design purposes.

Experimental Bond Behaviour of Glued-In Rod Connection for Mengkulang Glulam under Pull-Out Loading

Mechanical joint and adhesive joint are the two most common types of timber connections. In the case of timber construction, bonded-in rods offer a long-term, aesthetically acceptable alternative to some of the more conventional steel moment connections. Bonded-in rod connections in timber need many desirable attributes inefficiency, manufacture, performance, aesthetics and cost. This paper presents pull-out experimental testing for glued-in rod made of Mengkulang (tarrietia javanica) glulam joints. Hundred and seven (107) specimens were prepared, each with a single glued-in rod parallel and perpendicular to the grain. The steel treaded rod with a diameter of 12 mm, 16 mm and 20 mm with three numbers of adhesive (Sikadur-30) thicknesses of 2 mm, 3 mm and 4 mm were used in this experiment. The pull-out tests observations were on the effects of adhesive thickness, parallel and perpendicular grain directions and modes of failure of the specimens. The result obtained that 4 mm adhesive thickness was the strongest and parallel specimens showed better results than the perpendicular specimens. The pull-out failure modes are affected by the selected factors, i.e. the adhesive thickness, rod diameter and grain directions. Most of the specimens show failures in the timber besides the adhesive to timber interface.

Bond-Slip Relationship between Sand-Coated Polypropylene Coarse Aggregate Concrete and Plain Rebar.

Recycled plastic waste as an aggregate in concrete mixtures is one of the important issues in the construction industry since it allows the reduction of building weight and has beneficial effects on the environment. In addition, the bonding ability of this kind of lightweight concrete to reinforcement is also a prerequisite as a composite material in forming reinforced concrete structures. Therefore, in this study, the bond of plain rebar embedded in artificial lightweight aggregate concrete made from polypropylene plastic waste coated with sand was investigated. A pull-out test of nine group specimens was conducted to study the bond strength of 10 mm, 12 mm, and 16 mm diameter plain rebar embedded in polypropylene plastic waste coarse aggregates lightweight concrete (PWCAC), failure mode, and bond stress–slip relationship. The test results show that the bond–slip relationship and bond strength depend mainly on the bar diameter for PWCAC. Meanwhile, for all PWCAC specimens tested, the pull-out failure modes were observed. A bond equation for PWCAC was formulated by performing a regression analysis on the experimental results and afterward was combined with an existing bond–slip equation for normal concrete to have the bond–slip formulation for the lightweight concrete studied. The comparison between the model and experimental results indicates a close agreement.

Effects of Electrode Combinations on RSW of 5182-O/AlSi10MnMg Aluminum

Aluminum is a key lightweight material for reducing vehicle weight and improving fuel efficiency and is used in wrought, extruded, and cast forms. There is little research on resistance spot welding (RSW) of wrought-to-cast dissimilar aluminum alloys. For this paper, two types of electrodes were developed, and 2.3-mm 5182-O wrought and 4-mm AlSi10MnMg die cast sheets were welded by RSW with different electrode combinations. The results demonstrate that electrode geometry significantly influences the weld nugget morphology, weld performance, and failure mode. The proprietary Newton ring electrode produces the largest weld nugget size and consistent weld performance. Through the optimized electrode combination, severe weld nugget migration problems can be addressed for RSW of dissimilar aluminum alloys. Furthermore, the fracture crack under the tensile shear load always starts from the AlSi10MnMg side but not on the 5182-O side due to work hardening and concentration of stress regardless of whether the welds failed in the interfacial failure or pullout failure modes.

Microstructure and mechanical properties of nanosecond pulsed laser welded Al–Cu–steel laminated structures

Al–Cu–steel laminated structures with configurations of Al/Cu/steel and steel/Cu/Al were obtained via nanosecond pulsed laser welding. Cavities occurred at the bottom welds in two joints. Full-penetration welds occurred more easily in steel/Cu/Al joints compared to Al/Cu/steel joints. The metallurgical reaction of Al and Fe was impeded by Cu. The eutectic (α-Al+θ) and θ-CuAl2 phases were predominant at the Al/Cu interface in the steel/Cu/Al joints, while (Cu, Fe) was the main phase in Al/Cu/steel joint. The average lap shear force of the Al/Cu/steel joints (51.2 N) was superior to that of steel/Cu/Al joints (37.2 N). The fracture for both joins occurred at the Al/Cu interface. The fracture morphologies indicated that smaller connection width and Al/Cu IMCs caused the weld pullout failure (WPF) mode in steel/Cu/Al joints. The larger connection area and presence of (Cu, Fe) solid solution were responsible for the interfacial shear failure (ISF) mode in Al/Cu/steel joints.

Microstructural and mechanical characterization of steel-DP780/Al-5052 joints formed using resistance element welding with concealed rivet cover

Resistance element welding (REW) with a concealed rivet cover (Q235) was used to join steel-DP780 and Al-5052. The macroscopic morphology and the microstructure were observed using optical microscopy and scanning electron microscopy. The mechanical properties of the joint were also tested. The results show that the intermetallic compound (IMC) formed at the Q235/Al interface is FeAl3, while the IMCs formed at the DP780/Al interface are Fe2Al5 and FeAl3. The welding current has a significant influence on the nugget size, peak load, average hardness of aluminum heat-affected zone, and the bearing area of the aluminum plate. There are three fracture models of the countersunk rivet REW joint under a tensile-shear force: the interface failure fracture model, the fusion pullout failure fracture model, and the heat-affected zone failure fracture model. At a welding current of 18 kA, the nugget pullout failure mode is observed, and the best mechanical properties of the joint are obtained. The shear resistance of the joint can reach up to 5712 N.

Similar and dissimilar resistance spot weldability of Q&P980 and TWIP1180 steels

The resistance spot weldability of the newly developed TWIP1180 and Q&P980 with different thicknesses was evaluated. The different sheet thicknesses, heat conductivities and melting points caused that the Q&P/TWIP spot welds showed significantly asymmetric weld nuggets, and correspondingly influenced the tensile shear properties and failure modes of the spot welds. Pullout or partial pullout failure modes were obtained for the Q&P/Q&P and Q&P/TWIP combinations under proper welding currents, while only interfacial failure mode was observed for the TWIP/TWIP combination owing to the high strength and large thickness. Furthermore, the proper welding lobe for the Q&P/TWIP combination was obtained, which was crucial for the application of TWIP1180 and Q&P980 in automobile industry.

Effect of hole perpendicularity error and squeeze force on the mechanical behaviors of riveted joints.

In the automatic drilling and riveting process, the perpendicular error of the hole is inevitable, which has a great influence on the assembly quality. In the current research, the shear and pull-out behaviors of riveted joints under different perpendicularity errors and squeeze forces were investigated and compared by the quasi-static tests. The fracture of the failed samples was characterized by a scanning electron microscope and the formation process of fracture was discussed. The failure mechanisms of riveted joints were analyzed in detail to guide engineering applications. The test results demonstrated that the shear load and pull-out load of riveted joints increased slightly with the increase of the tilt angle from 0° to 4°. The perpendicularity error did not affect the shear and pull-out failure modes of the riveted joints. However, the squeeze force had a significant effect on the failure modes of the pull-out samples. Fracture analysis showed that the failure of all shear samples occurred at the rivet shaft. Besides, when the squeeze force increased from 15 kN to 23 kN, the failure modes of the pull-out samples changed from the sheet to the rivet itself.

Influence of scan line spacing on nanosecond pulse laser welding of 6063 Al to steel thin sheets

Nanosecond pulsed laser welding of 316L stainless steel and 6063 aluminum alloy thin sheets was performed. The influence of scan line spacing on the joining process was clarified. Large explosive hole and hot cracking defects including radial cracks and arc-shaped cracks occurred in the joint caused by excessive heat accumulation when the line spacing was 0.02 mm. The joints without oxidation were obtained. The thermal-induced penetration increment (TIPI) decreased with the increase of line spacing and reached the maximum value of about 162.24% with the line spacing of 0.02 mm. Fe2Al5 and FeAl phases probably were produced at all the line spacings. However, FeAl and α-Fe phases in the form of banding structures were possibly generated only with the line spacing of no less than 0.06 mm. The shear force test results indicated that the maximum shear load of 158.8 N was achieved at the line spacing of 0.06 mm due to the large bonding area and fewer defects. Three fracture paths, namely, button pullout failure (BPF), interfacial failure (IF) and mixed fracture (MF) mode of BPF and IF were produced. The heat affected zone was the origin of BPF mode. Local deformation, pores and Fe-Al brittle phases led to the fracture paths of IF and MF.

A Unified Model for Analyzing Comprehensive Behaviors of Deepwater Anchors

Anchors may exhibit various complicated behaviors in the seabed, especially for deepwater anchors including gravity installed anchors (GIAs) and drag embedment plate anchors (drag anchors), stimulating the development of an efficient analytical tool that applies to a variety of anchors. The present paper introduces a unified model for analyzing different anchor behaviors in both clay and sand, consisting of unified concepts, mechanical models, and analytical procedure. The kinematic behaviors of the anchors are classified uniformly as three types, i.e., diving, pulling out, and keying. By utilizing the least-force principle, various anchor properties, such as the ultimate pullout capacity (UPC), failure mode, movement direction, embedment loss, and kinematic trajectory, can all be determined by the combination and analysis of the three behaviors. Applications of the model are demonstrated summarily, by solving the UPC and the failure mode of anchor piles and suction anchors, the kinematic trajectory of drag anchors in a single soil layer or layered soils, the maximum embedment loss (MEL) of suction embedded plate anchors (SEPLAs) and OMNI-Max anchors, and the kinematic behavior of OMNI-Max anchors. Compared to existing theoretical methods, this unified model shows strong applicability and potentiality in solving a variety of behaviors and properties of different anchors under complicated seabed conditions.

Evaluation of Mechanical and Thermal Properties of Jute and Ramie Reinforced Epoxy-based Hybrid Composites

ABSTRACT In this study, the hybrid composites were prepared from ramie and jute natural as reinforcement, an epoxy polymer as a matrix, and SiC and cellulose as fillers via hand layup process. Mechanical and thermogravimetric analysis was carried out to quantify the effect of reinforcement on hybrid composites and evaluate their mechanical properties and thermal stability. The mechanical tests showed improvement in tensile and flexural strength of the hybrid composites with increasing content of bidirectional woven ramie fiber, and decreased with increased content of chopped jute fiber. The Izod impact test results revealed that chopped jute fiber form could resist more impact load when compared with woven ramie mat fibers. Hence, the impact energy increased with the increased content of chopped jute fiber in the hybrid composites. The surface morphological analysis of hybrid composites revealed the fiber pullout, cracks, and other failure modes of the hybrid composite using SEM analysis.