Dominant Failure Mode Research Articles

Experimental and numerical investigation on bearing behavior of hybrid thin/thick-ply composite laminates

Experimental and numerical studies were carried out to characterize hybrid thin- and thick-ply composite laminates and assess modelling capabilities. Five different composite laminates were manufactured using a single material system with varying proportions of thin plies (0%, 50%, and 100% thin-ply). Bearing tests were performed and the results from the tests were investigated. The results showed that performance, in terms of bearing strength at onset of damage and ultimate bearing stress, increased proportionally with the increasing amount of thin plies within the laminate. Microscopic examination of the failure modes for all laminates was performed at the center of the hole to determine the dominant failure mode. The numerical investigation uses a highly detailed mesoscale model previously validated for crash simulations but never used successfully to bearing damage areas. The results showed a good correlation regarding both the load response and the morphology of damage.

Seeding ductile nanophase in ceramic grains.

Transgranular brittle fracture is the dominant failure mode of brittle materials, including ceramics and ceramic matrix composites. However, strengthening these materials without sacrificing their toughness has been a big challenge. In this study, an innovative approach is proposed to achieve coordinated strengthening and toughening of ceramics-based composites by introducing specific ductile coherent nanoparticles into ceramic grains. As an example, the WC-Co cemented tungsten carbides were used to demonstrate how this brittle material can achieve ultrahigh strength without losing toughness by seeding metallic nanoparticles inside WC grains. The mechanisms for inducing the formation and modulating the amount, size, and distribution of such nanophase within the ceramic grains were disclosed. The fraction of transgranular ruptures of the brittle ceramic phase was reduced significantly due to the presence of the ductile coherent in-grain nanoparticles. Both the strength and strain limit of the cemented carbides were remarkably increased compared to their counterparts reported in the literature. The coordinated strengthening and toughening strategy proposed in this work is applicable to a broad range of ceramics and ceramic matrix composites to obtain superior comprehensive mechanical properties.

Superplastic-like flow behavior in Al0.2CoCrFeNiMo0.5 high entropy alloy

High temperature tensile experiments were performed on Al0.2CoCrFeNiMo0.5 high entropy alloy in the temperature range of room temperature (RT) to 900 °C. It exhibited good resistance to softening up to 700 °C, and thereafter a rapid decrease in the strength was observed. Superplastic-like tensile elongation of ∼ 275 % was observed at a strain rate of 1x10-3 s−1 and at a temperature of 900° C. Tensile experiments at different strain rates along with strain rate jump experiments at 900 °C showed a strain rate sensitivity of ∼ 0.32. Kernal Average Misorientation (KAM) maps at the gauge and grip portions along with texture pole figure analysis suggesting that dislocation glide might be the active deformation mode responsible for large tensile elongation. Cavitation along the secondary phase-matrix interphase was the dominant failure mode.

Impact response of filament-wound structure with polymeric liner: Experimental and numerical investigation (Part-A)

Filament wound pipelines and Type IV composite pressure vessels (CPVs) constitute polymeric liners and are extensively used to transport and store petroleum products, hydrogen, and compressed natural gas (CNG). The polymeric liner does not share much pressure load; hence, the composite layers share most of the load. The situation gets worse under transverse impact loads on such structures. For the polymeric liner to be effectively used in pipelines and CPVs, it is crucial to study impact response through testing and computational methods. This article presents experimental and numerical investigations of the transverse low-velocity impact response of filament wound samples. High-density polyethylene (HDPE) liner was adopted, and carbon fiber (T700) continuous filaments with epoxy resin were wound over the liner with several layers. A drop-weight impact loading with 40 J energy has been applied to the fabricated samples. The development of impact damage was assessed using the finite element method, and the damage modes have been discussed. The specimen remains unperforated at the chosen energy level. Though HDPE is ductile, however at impact loads liner damage was encountered, displaying a brittle fracture. At higher strain rates, the material reaches its brittle fracture point sooner, leading to failure. The material breaks as brittle due to its inability to dissipate impact energy quickly, resulting in fracturing instead of deformation. Fiber damage was scarcely seen; however, matrix damage has been the dominant failure mode at the chosen impact energy. Comparisons between the simulation and test findings were made, and they agreed on force-time and force-displacement histories.

Mechanical performance of a bond-type anchorage system for CFRP cable exposed to elevated temperature

Both high-temperature pullout tests without and with pre-tension load were conducted on the bond-type anchorage system specimens with bonding medium of UHPC (Ultra-high Performance Concrete) for Carbon fiber reinforced polymer (CFRP) cable in order to fully understand the bonding behavior of CFRP cable-UHPC interface under high temperature. The variation laws of ultimate pullout load, average bond strength of CFRP cable-UHPC interface and slippage corresponding to ultimate pullout load were uncovered in two types of high-temperature pullout tests. Then, the bond performances of CFRP cable-UHPC interface in high-temperature pullout tests with pre-tension load ratio from 0.2 to 0.6 and target temperature in the range of 100–210 ℃ were compared to these in high-temperature pullout tests without pre-tension load in order to identify the effect of temperature-load path. Finally, theoretical models for determining average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable for the bond-type anchorage system under high temperature were developed by incorporating effects of high temperature and pre-tension load ratio. The obtained results demonstrate that the dominant failure mode of the bond-type anchorage system in high-temperature pullout tests is slip failure of CFRP cable-UHPC interface, and shear failure morphologies of embossed rid for CFRP tendon are closely correlated with target temperature. In high-temperature pullout tests without pre-tension load, the average bond strength of CFRP tendon-UHPC interface gradually decreased as the increasing target temperature, the corresponding attenuation ratios in temperature ranges of 25–300 ℃ and 300–400 ℃ are 84% and 47%, respectively. In high-temperature pullout tests with pre-tension load, the average bond strength of CFRP tendon-UHPC interface approximately linearly decreased as the increasing target temperature or pre-tension load ratio. The presence of pre-tension load results in acceleration of damage of CFRP cable-UHPC interface, and the damage degree is proportional to pre-tension load. The developed theoretical models of mechanical properties for the bond-type anchorage system exposed to high temperature can accurately predict average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable.

In-situ manipulation of TiB whisker orientation and investigation of its high-temperature mechanical properties in titanium matrix composites

“SPS pre-sintering + SPS reactive hot extrusion” (SPSHE) is a promising technique for manipulating the orientation of TiB whiskers (TiBw) in discontinuously reinforced titanium matrix composites (DRTMCs). In the current study, (12.4 vol % TiBw +2.9 vol % TiC)/Ti6Al4V composites were prepared using SPSHE technology, successfully achieving both the normalization of TiBw orientation and a high aspect ratio. Specifically, the [010] axis of TiBw was aligned with the extrusion direction, and the average aspect ratio was 24.86. Tensile tests were conducted on the DRTMC samples at temperatures of 873 K, 923 K, and 973 K. The results demonstrate that SPSHE significantly enhances the high-temperature strength of the composite. At 873 K, the DRTMC exhibited an exceptionally high tensile strength of 732.2 ± 20 MPa. The main strengthening mechanisms of the DRTMC include load transfer strengthening from TiBw and TiC particles, solution strengthening, fine grain strengthening and dislocation strengthening. Moreover, at 873 K and 923 K, the dominant failure mode of the reinforcement was a load-bearing fracture. However, as the test temperature increased to 973 K, a mixed failure mode of load-bearing fracture and interface debonding was observed in the reinforcement.

Investigating seismic behaviour of cold-formed steel moment frames with the welded through-plate flexural connection

The Cold-Formed Steel (CFS) construction in seismic regions requires carefully selecting and designing an approved seismic-force resisting system. Among the available seismically-resistant structural systems, the bolted CFS moment frames have recently gained some attention. However, given the currently existing design issues associated with the bolted connections in CFS moment frames, this paper seeks to conduct a numerical investigation into the potential substitution of bolt fasteners with the weld materials in CFS frames. The objective is to explore the possibility of including the welded connection as an alternative to bolted connections in subsequent editions of the ASCE 7 code. To this end, finite element models, consisting of two built-up CFS beams and twenty-three flare-bevel-groove and fillet weld specimens, are initially validated against the cyclically and monotonically loaded tests with data available in the relevant literature. Subsequently, the verified weld and CFS beam models are incorporated in the simulation of thirty-four CFS beam-to-column welded moment connections, each differing in beam dimension, weld length and size, and gusset plate thickness. The built-up beams comprise back-to-back and lip-to-lip double C-section profiles. Stress variations along the weld lines, derived initially from nonlinear finite element analyses and then computed from the theoretical elastic analysis, are compared to establish a basis for categorizing stress distribution patterns in the longitudinal welds. Finally, six CFS frames assembled with the welded moment connection and subjected to a combined column axial compression and cyclic lateral drift are examined, resulting in an estimated seismic modification coefficient, R, equal to 3.8. Overall, the welded moment connections demonstrate a stable seismic response with an average ductility ratio, μ, of 2.7. The dominant failure mode is a locally developed ductile fracture in the two end segments of the longitudinal welds, identified as critical regions.

Research on the Mechanical Performance of a Mountainous Long-Span Steel Truss Arch Bridge with High and Low Arch Seats

The Loushui River Bridge is a mountainous long-span steel truss arch bridge with high and low arch seats. The design and construction of the bridge follow the principle of minimizing environmental damage and promoting sustainable development. In this article, the mechanical performance of this bridge is investigated experimentally and numerically at both the construction and operation stages. A series of validated finite element models were established for linear and nonlinear analyses by introducing geometric imperfections, geometric nonlinearities, and material nonlinearities. Then, several optimized models based on different types of design are compared with the original structure. The results indicate that the stability of the asymmetric bridge met the design requirements in both the construction and operation stages. However, the lateral stability and stiffness of the asymmetric bridge are weak due to the wind hazard that occurred in its mountain ravine. The out-of-plane instability from the short half-arch is the dominant failure mode, and the weakest area is where the arch ribs intersect with the bridge deck. It can be solved by adding more cross bracings without affecting the clearance above the bridge deck or by improving the material intensity of the arch.

A novel microstructure-informed machine learning framework for mechanical property evaluation of SiCf/Ti composites

In this work, a novel microstructure-informed machine learning (MIML) framework is proposed for the longitudinal ultimate tensile strength (UTS) evaluation and the construction of microstructure-property linkages of titanium matrix composites (TMCs). The main components of the MIML framework include (i) high-fidelity simulation and dataset generation using finite element method (FEM), (ii) the quantitative characterization of microstructures obtained by 2-point cross-correlation analysis and principal component analysis, (iii) the extraction of structure-property linkages based on support vector regression model and (iv) the validation of MIML by experimental data. The fiber breakage observed by advanced microstructure characterization is considered as the dominant failure mode during mechanical tests of TMCs, which is embedded in the FEM simulations. The MIML approach reaches capable accuracy in UTS prediction of TMCs using FEM-generated datasets and trained MIML is validated by experimental data. In addition, the permutation importance-based method is utilized to accurately identify the key feature parameters related to UTS. The first two principal components of microstructural reduced-order representation are recognized as highly relevant features for UTS. The well-trained MIML model is a promising tool in the evaluation of the mechanical property, and further provides a technical chain for the establishment of microstructure-property linkages of multi-phase composites.

An adaptive structural dominant failure modes searching method based on graph neural network

Dominant failure modes (DFMs) of structural systems are integral to life prediction and reliability assessment. However, the computational efficiency of existing DFMs searching methods is constrained by neglecting the structural non-Euclidean properties. To break free from this shackle, this paper proposes a DFMs searching algorithm based on the graph neural network (GNN). The proposed algorithm can adaptively identify graph samples representing DFMs via completing graph classification. First, the target structural system is converted into an undirected graph to preserve its topological features. Second, a hierarchical graph attention mechanism is developed to establish the mapping relationship between structure intrinsic properties and DFMs. Finally, two adaptive sample selection strategies are devised to iteratively search DFMs and supplement graph datasets. In order to reduce the number of reliability analyses, the algorithm will terminate prematurely when unable to identify new DFMs. A 2D truss and a 3D frame are selected to test the computational efficiency and stability of the algorithm. The search results indicate that, despite providing different initial training sets, this GNN-based algorithm still converges to DFMs consistent with the result of Monte Carlo Simulation (MCS). Compared to the genetic algorithm (GA) and the β-unzipping method, the proposed algorithm exhibits higher computational efficiency.

Experimental study on the seismic performance of non-compact H-section steel frames

In order to assess the seismic performance of steel frame systems with non-compact members, cyclic tests were conducted on three full-scale frames incorporating beams and columns of varying plate width-thickness ratios. The seismic performance of these specimens, including failure modes, hysteresis curves, load-bearing capacities, ductility, and energy dissipation capabilities was thoroughly examined. The test results indicated that the dominating failure mode observed in all the specimens was the local buckling deformation occurring at the beam end and column bottom zones, and the occurrence of the first concentrated local failure would lead to the ultimate load-bearing state of the frames. Moreover, the occurrence sequence and development degree of the buckling deformations had a significant effect on the seismic performance of the frames. These findings suggest that reasonable combinations of beam and column sections should be carefully considered to retain rational balance between load-bearing capacity, ductility and energy dissipation capabilities for non-compact frames.

Probability-Based Design of Reinforced Rock Slopes Using Coupled FORM and Monte Carlo Methods

The efficiency of the first-order reliability method (FORM) and the accuracy of Monte Carlo simulations (MCS) are coupled in probability-based designs of reinforced rock slopes, including a Hong Kong slope with exfoliation joints. Load–resistance duality is demonstrated and resolved automatically in a foundation on rock with a discontinuity plane. Other examples include the lengthy Hoek and Bray deterministic vectorial procedure for comprehensive pentahedral blocks with external load and bolt force, which is made efficient and more succinct before extending it to probability-based design via MCS-enhanced FORM. The FORM–MCS–FORM design procedure is proposed for cases with multiple failure modes. For cases with a dominant single failure mode, the time-saving importance sampling (IS) and the fast second-order reliability method (SORM) can be used in lieu of MCS. Two cases of 3D reinforced blocks (pentahedral and tetrahedral, respectively) with the possibility of multiple sliding modes are investigated. In the case of the reinforced pentahedral block, direct MCS shows that there is only one dominant failure mode, for which the efficient method of importance sampling at the FORM design point provides fast verification of the revised design. In the case of the reinforced tetrahedral block, there are multiple failure modes contributing to the total failure probability, for which the proposed MCS-enhanced FORM procedure is demonstrated to be essential. Comparisons are made between Excel MCS and MATLAB MCS.

Improving the Understanding of Landslide Development in Alpine Forest Regions Using the InSAR Technique: A Case Study in Xiaojin County China

Employing a small baseline subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) and hotspot analysis, this study identified 81 potential landslides in a 768.7 km2 area of Xiaojin county, eastern Tibetan Plateau. Subsequent time-series deformation analysis revealed that these potential landslides are in the secondary creep stage. The newly identified landslides were compared to a landslide inventory (LI), established through field surveying, in terms of causative factors, including altitude, slope, relief amplitude, distance to river, distance to road, and slope curvature. From the comparison, the InSAR technique showed the following advantages: (1) it identified 25 potential landslides at high altitudes (>3415 m) in addition to the low-altitude landslides identified through the field survey. (2) It obtained approximately 37.5% and 70% increases in the number of potential landslides in the slope angle ranges of 20°–30° and 30°–40°, respectively. (3) It revealed significant increases in potential landslides in every relief amplitude bin, especially in the range from 58 m to 92 m. (4) It can highlight key geological factors controlling landslides, i.e., the stratigraphic occurrence and key joints as the InSAR technique is a powerful tool for identifying landslides in all dip directions. (5) It reveals the dominant failure modes, such as sliding along the soil–rock interface and/or interfaces formed by complicated combinations of discontinuities. This work presents the significant potential of InSAR techniques in gaining deeper knowledge on landslide development in alpine forest regions.

Analyzing the effect of fiber path curvature on the fracture behavior of braided composite cylinders; experimental study

AbstractDifferent failure modes occur in textile‐reinforced composite under applied loads. Fracture mechanism of braided composites are closely related to the geometry of braids. In the present study, fracture mechanism of glass/epoxy braided composite cylinders is investigated under tensile loads. For this purpose, glass/epoxy braided composites were fabricated using braids with braiding angles of 30°, 45°, and 57° to find the role of fiber path on the fracture mechanism. To determine the fiber path, helixes on the cylinders with aforementioned angles was considered and analyzed. New fixtures (jaws) were designed and manufactured for tensile testing of cylindrical composites. Tensile tests were carried out on the prepared samples to evaluate the failure modes of composites. The SEM micrographs of samples are provided after tensile test. Various failure modes were observed regarding the angle of the braid. Fiber breakage, matrix fracture, and debonding are the dominant modes that occur in braided composites proportional to the angle of braids. Fiber breakage is the dominant mode in the 30° angle braid reinforced composite, while the dominant failure mode in the 57° angle braid reinforced composite is matrix fracture. In composites with a braid angle of 45°, a combination of fracture modes occurred. In addition, energy absorption as well as specific energy absorption (SEA) of braided composite cylinders were also investigated and obtained from load–displacement curves. The results showed that the reinforced composite with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.Highlights Fiber breakage is the dominant mode at the 30° angle braid reinforced composite. The dominant failure mode at the 57° angle braid reinforced composite is matrix fracture. In composites with the braid angle of 45°, a combination of fracture modes occurred. The composite reinforced with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.

Web Stiffening of Additive Manufactured Polylactide (PLA) Railroad Tracks Using Fiberglass Wrapping

Three-dimensional (3D) printed railroad tracks can properly address the rendering of a variety of topographic profiles of naturally occurring landscapes and reduce construction costs. Load tests of PLA railroad tracks found that web failure is a dominant failure mode. This paper evaluates the web stiffening strategies of additively fabricated PLA railroad tracks for rail-guided, micro-people movers (MPMs). To strengthen the track web, web-widening with additional PLA material and stiffening using composite reinforcement using glass fiber reinforced polymer (GFRP) wrap have been investigated. The composite wrapping technique was conducted by bonding fiberglass cloth to both sides of the web using a polymeric resin. Flexural load tests were conducted on the specimens with different infill volume percentages. A linear trend was observed on the peak bending capacities of specimens with PLA infill fiber contents ranging between 20% to 100%. Different failure modes were observed for the different percentage specimens during the tests. When compared to their unreinforced counterparts, the 60% infill specimen had the largest increase in strength about 1,500 N in bending with the addition of GFRP wrap. The tangent stiffnesses of all samples were calculated which showed the 100% infill specimen had the highest increase of approximately 50%. The wrapping reinforcement was found to significantly modify the failure mechanisms of the 3D-printed tracks with different infill volume percentages. The strengthening of the 3D-printed tracks using GFRP wrapping is also shown to be similar to the widening of web sections of the additively printed railroad tracks.

Effect of Irrigation with Different Solutions on Push out Bond Strength of Root Canal Obturation Materials

Evaluate push out bond strength (PBS) of endodontic obturation materials after washing by NaOCl, EDTA, and MTAD. Materials and methods: 30 mandibular premolars were utilized. Root canal instrumentation of all samples was achieved by ProTaper universal files to size F4. Samples were distributed to 3 groups; each group involved 10 samples as the following: Group1- samples were lastly washed by 5 ml of 5.25% NaOCl for 5 minutes. Group2- samples were lastly washed by 5 ml of 17% EDTA for 5 minutes. Group3- samples were lastly washed by 5 ml of MTAD for 5 minutes. All samples were filled by single cone technique with AH Plus sealer, and F4 ProTaper gutta-percha cone. 3 sections of 2 mm thickness were transected from every sample at 3, 7, and 11 mm from root apex, which represented apical, middle, and coronal sections consecutively. PBS was tested by universal digital testing device. Failure modes were assessed by stereomicroscope at 40 X magnification. Lastly, collected data was analyzed statistically. Results: MTAD group revealed significant greatest mean of PBS followed by EDTA group, and NaOCl group revealed significant least mean of PBS. In all groups, greater mean of PBS was in coronal section followed by middle section while, lesser mean of PBS was in apical section though, the differences among them were not significant within the same group. Mixed and cohesive failures were most dominant modes of failure in MTAD, and EDTA groups. While, in NaOCl group adhesive, and mixed failures were most dominant. Conclusions: last washing with MTAD is better than that with EDTA, and NaOCl in terms of greatest PBS.

Bond properties between lapped steel rebars and UHPC under direct tension

Ultra-High Performance Concrete (UHPC) is a highly advanced cement-based composite that offers higher mechanical properties and exceptional durability over Normal-Strength Concrete (NSC). Bond properties between steel rebars and UHPC are the key to designing reinforced UHPC structures. The goal of this study was to characterize the bond properties between lapped steel rebars (uncoated) and UHPC. A total of 20 modified pullout tests having two-row lap splices were performed to examine the variation of diameters of 10, 14, 20, 25 and 32 mm. It was shown that the splitting of UHPC covers was a dominant failure mode, and samples with smaller bar diameters exhibited good ductility. Higher bond strengths were found in samples with smaller bar diameters. Specifically, bond strengths in samples having diameters of 20 mm, 25 mm, and 32 mm showed reductions of 14.8 %, 27.6 %, and 35.2 % in comparison to those featuring a diameter of 10 mm. The distributed curves of bond stress with two peaks were identified when maintaining a lapped length of four times the bar diameter. Furthermore, the mechanical model for lapped steel rebars in UHPC and the theoretical equation for calculating the bond-splitting strength and minimum lapped length were presented and validated by the available studies.

Effect of interface temperature on low‐velocity impact response of injection over‐molded short/continuous fiber reinforced polypropylene composites

AbstractInjection over‐molded short/continuous fiber reinforced composites are a unique class of materials for fabricating lightweight components having complex geometries in automotive manufacturing due to their higher specific mechanical properties, lower assembly cost, and short production cycle time. The influence of interface temperature on the low‐velocity impact response of short/continuous fiber‐reinforced polypropylene was experimentally investigated by varying the melt temperature. The over‐molded specimens fabricated at an interface temperature considerably higher than the melting point of polypropylene exhibited a 12% enhanced peak load with less impact damage compared with specimens over‐molded at a lower interface temperature. Optical analysis of impacted specimens over‐molded at lower interface temperature revealed interface debonding and insert delamination. Whereas insert delamination alone was observed for the specimens fabricated at higher interface temperature. The specimens over‐molded at high interface temperature exhibited less impact energy absorption and high compression strength after impact because of their strong interfacial adhesion.Highlights Impact energy absorption is less if melt temperature is high in injection over‐molding. Higher melt temperature enhances interface bonding by raising interface temperature. Interface debonding and insert delamination are the dominant impact failure modes. The compression strength after impact has increased with higher melt temperature. Impact and compression strength after impact is governed by the interfacial strength.

Comparative Evaluation of Application of Universal Bonding on the Microtensile Bond Strength of Light Cure and Dual Cure Composites Bonded to Dentin.

Objectives: There is limited knowledge on the efficacy of universal adhesives when used in different etching modes. The aim of this study was to evaluate the microtensile bond strength (µTBS) to dentin using universal adhesives with light-cure and dual-cure composites. Materials and Methods: In this in vitro experimental study, the occlusal third of 60 caries-free human molars were removed and the exposed surfaces were treated and allocated to 10 groups (N=6). Two different bonding agents (Single Bond Universal, G-Premio) were used to bond 2 different composite resins (Z250 light-cure and CoreFlo DC dual-cure) to dentin, using etch-and-rinse (E&R) and self-etch (SE) modes. Single Bond 2 was applied in E&R mode on wet dentin to serve as control. The specimens were sectioned into 1×1 mm2 sticks with a precision saw. A microtensile testing machine was used to measure the µTBS of the specimens with a crosshead speed of 0.5 mm/min. Data were analyzed using three-way ANOVA and Bonferroni post-hoc test (α=0.05). Results: The Single Bond Universal group in SE mode with light-cure composite yielded the highest (39.24MPa), and the G-Premio SE group with dual-cure composite produced the lowest (13.65MPa) mean µTBS (P<0.05). The dominant failure mode was adhesive, in all groups. Conclusion: The bonding agent had a significant effect on µTBS of composite to dentin, but different composites and different etching modes were not significantly different in this respect.

Tensile behavior and failure modes of expansion anchors in High-Performance Steel Fiber Reinforced Concrete (HPSFRC)

To investigate the tensile(pullout) behavior of expansion anchors in High-Performance Steel Fiber Reinforced Concrete(HPSFRC), 30 valid unconfined tension(pullout) tests on expansion anchors, studying the effects of different steel fiber content(0.0 %, 0.5 %, 1.0 %, and 1.5 %), embedment depths(25 mm, 35 mm, and 45 mm), and anchor diameters(10 mm and 12 mm) on the tensile behavior of anchors. A total of seven failure modes, including different types of mixed modes, are observed. The incorporation of fibers reduces the anchorage stiffness, increases the ductility, and improves the post-peak performance of the tensile behavior of anchors. Effective embedment depth(Hef)exerts a great influence on the failure mode; as Hef increases, the dominant failure mode transits from the concrete breakout to the pull-through and mixed failure modes, and finally the steel failure mode. The increase in Hef also leads to increases in the ultimate tensile strength of the anchor(Nu) and the anchorage ductile. For the same Hef and fiber content, compared to the smaller diameter(D), Nu for the larger diameter is larger but the pullout ductility is weaker. A modified model considering the influence of steel fibers is proposed to predict Nu of CB mode in HPSFRC, and it results in more accurate predictions compared to the existing prediction models(CCD model, Toth model). An existing prediction model for PT mode in normal concrete has been proven to be applicable for anchors HPC/HPSFRC.