Pull-out Length Research Articles

Mechanical behavior and failure mechanism of 2D-SiCf/SiC composite under dynamic tensile loading through experimental and numerical investigation

The mechanical behavior of 2D-SiCf/SiC composite is investigated under both quasi-static (strain rate of 10-5 and 10-4s-1) and dynamic loading conditions (strain rate of 102s-1) through a combined experimental and numerical approach. The damage evolution process is monitored using digital image correlation, while failure mechanisms are analyzed through in-situ and post-test observations. Strain rate has a significant effect on tensile behavior of 2D-SiCf/SiC composite, including stress-strain behavior, damage accumulation process, fracture mode and fiber pull-out length. By integrating theoretical models with a detailed meso-scale finite element model, changes in constituent properties due to strain rate are quantified, and the evolution patterns of different damage modes under varying strain rates are explored. The study revealed that the strain rate effect is primarily driven by the enhancement of interfacial shear stress, matrix strength, and in-situ fiber strength as the strain rate increases.

Dynamic tensile intralaminar fracture and continuum damage evolution of 2D woven composite laminates at high loading rate

The intralaminar tensile failure of 2D woven composites under dynamic tensile load was investigated in this paper. Compact tension samples were tested at high loading rate with an electromagnetic Hopkinson bar system. The strain field was obtained with high-speed imaging and digital image correlation, and the J-integral method was employed to obtain the fracture toughness and corresponding R-curve. The continuum damage evolution of intralaminar failure was then analyzed by tracking the opening near the initial crack tip. It is found that the dynamic intralaminar fracture toughness is decreased by 51% compared to the quasi-static condition, the continuum damage evolution and its dependence on loading rate have been reported as well. The failure mechanisms were studied with thermal imaging and scanned electron microscopy, shorter fibre pull-out length and thinner failure process zone may be responsible for the reduced toughness at high loading rate.

Pull-out resistance of connected K-wires for osteosynthesis: development of a numerical model

A predictive finite element model was developed to investigate the best configuration of a fixation pins system consisting of two K-wires inserted in a synthetic model (Sawbones®) at different angles and secured to a connecting rod. Two key parameters were considered to determine the best configuration delivering the higher pull-out strength and lower pull-out length: the diameter and insertion angle. Results show that as the diameter and insertion angle increased, the pull-out force increased, while the pull-out length decreased. Results are successfully compared with available experimental data in literature. This model can be used as an alternative to experimental study.

Experimental and Parametric Study on Rotational Performance of Through-Tenon Joints in Traditional Timber Structures

ABSTRACT The rotational capacity of mortise-tenon joints is crucial for stability in traditional timber structures. However, these joints are influenced by various factors such as environmental conditions and internal features, impacting their rotational performance over time. To assess these influences, four groups of through-tenon joints with different small and large tenon lengths were constructed and tested. Deformation characteristics, hysteresis, bearing capacity, stiffness, and energy consumption of the joints were investigated. Finite element models were created and verified through testing. An orthogonal design scheme analyzed the effects of parameters and their interactions on rotational performance. The results indicated that increasing the length of the smaller tenon improved tenon pull-out length and ductility, while simultaneously reducing bearing capacity, stiffness, and energy dissipation. Tenon dimensions and the ratio of small tenon length to total tenon length were found to significantly impact peak moment. Critical parameters affecting rotational performance included tenon length, elastic modulus perpendicular to the grain, and the gap between the tenon and mortise.

Experimental and numerical analysis of CMCs mechanical properties under high-temperature thermal gradient environment

This paper carried out a high-temperature thermal gradient cycling test of ceramic matrix composites (CMCs), investigating the failure characteristics of CMCs in non-uniform high-temperature environments. The result shows that the damage characteristics of CMCs under thermal gradient environments are significantly different from those under uniform temperature environments. The SiC fiber pull-out lengths at different yarn fractures have obvious differences in the thermal gradient direction. The thermal stress damage propagation pattern of CMCs under the thermal gradient environment is revealed by numerical analysis, and its residual mechanical properties under different thermal gradient environments are predicted. The numerical results could be adopted as a theoretical basis and suggestions for temperature control of CMCs components in practical applications.

Experimental study on the seismic performance of a full-scale two-story traditional timber frame on sloped land

In traditional timber structures built on hilly areas, columns of varying lengths are utilized to accommodate sloped terrain. This structural feature renders these structures more susceptible to seismic damage than structures built on flat land. To investigate the seismic performance of traditional timber structures on sloped land, the quasi-static test was conducted on a full-scale two-story timber frame on sloped land (FSL), while an identical frame on flat land (FFL) was served as a comparative reference. This study analyzed the deformation characteristics, bearing capacity, and energy dissipation capacity of the frame on sloped land, as well as its weak positions and failure mechanisms. The test results indicate that the frame on the upper ground is the weak position compared to the frame on flat land. Short columns of the upper frame have greater inclination angles, leading to larger pull-out lengths of the mortise-tenon joints, and the column foot becomes more susceptible to slipping and lifting. Although the FSL has a greater bearing capacity than the FFL under the same horizontal displacement, it experiences a more significant deformation and is more prone to tenon failure and column foot sliding out of the foundation stone. With excessive deformation, gravity becomes a detrimental factor for structures on sloped land to resist horizontal overturning moments, which would accelerate the collapse of the structure.

Influence of interfacial microstructure on the mechanical properties of SiC/SiBCN composites

SiC/SiBCN composites were prepared via polymer infiltration and pyrolysis technique (PIP) and the influence of the interfacial microstructure on the mechanical properties of the composites was investigated. In this paper, an amorphous SiOC layer was observed at the fiber-matrix interface for the first time. Formation of the SiOC layer stems from SiO gas formed inside the ceramic matrix may diffused towards the interface and reacted with the carbon-rich layer of SiC fibers to form Si atom. Si atom dissolved in the O–C molecular network to form a 100 nm chemical bonding SiOC layer, which caused the SiC fibers to pull out in a whole bundle and the pull-out length was short, leading to a composite flexural strength of only 143 ± 30 MPa. By introducing SiC coating, SiC fibers were effectively protected from chemical reactions, and the coating acted as a barrier to the diffusion and migration of the matrix elements to the interface and weakened the interfacial bonding strength (IFBs), in which IFBs decreased from 266 ± 19 MPa to 170 ± 10 MPa. Hence, the flexural strength of composites increased up from 143 ± 30 MPa to 388 ± 16 MPa.

Tensile properties of 2D-C/SiC composites at temperatures up to 1873 K at wide-ranging strain rates

We determined the tensile properties of 2D-C/SiC composites at temperatures up to 1873 K with a wide range of loading rates (10−3 s−1 and 400 s−1) in argon and air. We developed a high-temperature Hopkinson tensile bar with tensile strength based on the loading rate, temperature, and oxidation. Under high loading rates, tensile strength was influenced by the nucleation of multiple cracks and the improvement of C-fiber pull-out length and interface strength. In argon, material component performance and thermal residual stress influenced the 2D-C/SiC high-temperature tensile properties. In air, oxidation damage significantly affected the tensile properties of 2D-C/SiC regardless of loading rate or temperature. This led to lower tensile strength and higher strain rate sensitivity. Our observations can enhance the understanding of the failure mechanism of thermo-chemo-mechanical coupling in 2D-C/SiCs and will provide guidance for safe application in extremely high-temperature conditions.

Direct shear strength of UHPC considering size effect: Theoretical model and experimental verification

The direct shear performance of UHPC is of great importance for UHPC members in some practical cases, such as shear key and corbels. However, there are seldom available theoretical methods in existing studies for determining the direct shear strength of UHPC. A theoretical model was developed in this study to predict the direct shear strength of UHPC which was supposed to be the superposition of those contributions of UHPC matrix and fibers. In this model, the shear contribution of fibers was theoretically determined using the average contribution rate of fibers in the force direction, i.e. the fiber effective factor Kf. This coefficient comprehensively revealed the effects of fiber orientation distribution, fiber efficiency and effective pull-out length. The fiber effective factors Kf in zones constrained by no, one-side and two-side moulds are 0.283, 0.408 and 0.641, respectively. The size effect caused by the wall effect of formwork was also considered in the determination of shear contribution of fibers based on Kf. The direct shear test on 14 UHPC Z-shape specimens was performed to verify the proposed model. Test results indicated that both the fiber content and the specimen size had certain influence on the direct shear strength of UHPC. The comparison with the predicted values showed that the proposed model provided relatively good predictions of the direct shear strength of UHPC.

Relationship between interfacial shear strength and impact strength of injection molded short glass fiber-reinforced thermoplastics

Short glass fiber-reinforced thermoplastics (SGFRTPs) are being used to reduce carbon dioxide emissions from transportation equipment, especially domestic vehicles, because of their properties and because they are lighter than metal or ceramic materials. Interfacial shear strength (IFSS) strongly affects mechanical properties of SGFRTPs, such as the impact strength. In recent years, investigations of IFSS and impact strength have been very active. Positive correlation between these properties is often reported, but no clearly defined quantitative relation has been found. This study used the short beam method and the notched Charpy impact test to elucidate IFSS and the impact strength of injection-molded SGFRTPs with varying fiber contents: IFSS decreases concomitantly with increasing fiber content; the notched Charpy impact strength increases concomitantly with increasing fiber content. Fiber pull-out occurred along the entire fracture surface. Findings confirmed that fiber pull-out occurred with both crack initiation and propagation, indicating that energy absorption in the impact test was entirely attributable to the frictional energy necessary for fiber extraction. Based on this conclusion, a mechanical model was developed to explain the notched Charpy impact strength of SGFRTP injection molded products in terms of their IFSS, pull-out fiber length, and fiber orientation angle. The impact strength calculated using the predicted results shows good agreement with the experimentally obtained results.

Characterizing and predicting the relationship between translaminar fracture toughness and pull-out length distributions under distinct temperatures.

The translaminar fracture toughness reflects the damage tolerance of a fibre-reinforced composite under longitudinal tension, which often governs the final failure of structures. One of the main energy-dissipation mechanisms that contributes to the translaminar toughness of composites is the fibre pull-out process. The present study aims to quantify and model the statistical distribution of fibre pull-out lengths formed on the translaminar fracture surface of composites, for the first time in the literature; this is done under different temperatures, so that the relationship between pull-out length distributions, micromechanical properties and the translaminar fracture toughness can be established. The fracture surfaces of cross-ply compact tension specimens tested under three different temperatures have been scanned through X-ray computed tomography to quantify the extent of fibre pull-out on the fracture surfaces; the distribution of pull-out lengths showed alarger average and larger variability with an increase in temperature, which also lead to an increase in translaminar fracture toughness. A similar trend has been captured by the proposed analytical model, which predicts the pull-out length distribution based on the analysis of quasi-fractal idealizations of the fracture surface, yielding an overall accuracy of more than 85%. This article is part of the theme issue 'Ageing and durability of composite materials'.

Determination of fibre tension fracture toughness of composite laminates at high loading rate

The dynamic fracture toughness of composite laminates in fibre tension failure mode is characterized here with compact tension (CT) sample, at loading rate of 25 m/s using bi-directional electromagnetic Hopkinson bars. Digital image correlation (DIC) with high-speed imaging is employed for obtaining the full-field strain fields. A dynamic J-integral method is proposed to analyse the dynamic fracture toughness, the kinetic energy and inertia effects involved in dynamic loading and crack propagation process has been analysed and calibrated. The fracture toughness of fibre tension failure at high loading rate is found to be about 25% lower than that in quasi-static load regime, and the R-curve effect under high loading rate is not significant than that in quasi-static load regime. It is suggested from X-ray CT and SEM images that the fibre pull-out length and size of failure process zone is reduced with increase in loading rate.

A mesomechanics-based analysis on the flexural behavior of ultra-high-performance concrete (UHPC) with different steel fiber lengths

This study investigates the flexural behavior of UHPC materials containing steel fibers of varying lengths. Mesomechanical analysis is performed according to the analytical pullout model, using actual measured fiber distributions. The flexural behavior of UHPC after cracking is simulated by superposing the fiber bridging and matrix softening curves. Subsequently, the evolution of stress–strain along the axial crack of UHPC is evaluated under different loading conditions. The obtained results indicate that longer steel fibers can efficiently improve the flexural behavior of UHPC. Moreover, the actual fiber orientation and pullout length distributions can be well fitted by two-parameter probability distribution (PDF) and Gaussian functions, respectively. Based on the micromechanical analysis, the fiber bridging behavior is overestimated under the assumption of 2D random fiber distribution, and it is underestimated under the assumption of 3D random fiber distribution. Interestingly, the length of the shear lag zone is independent of the fiber length, which is about 20.16 mm. The obtained results demonstrate that the compressive stress and strain at the top of the tested specimen gradually transform into tensile stress and strain at the opposite side. Interestingly, the stress of the specimens with fiber length of 20 mm are slightly higher than the specimens with fiber lengths of 6 and 13 mm, and the strain just lower than the specimens with fiber lengths of 6 and 13 mm in all crack propagation stages, respectively. This indicates that, in addition to the number of steel fibers, the stress/strain dispersion depends on fiber length.

Effect of fiber bending induced matrix shear behavior on machined surface quality in carbon fiber reinforced plastic milling

Fiber bending by the cutting tool is one of the dominant causes of fiber pull-out on machined surfaces during CFRP milling. During the bending, the polymer matrix between the fibers is subjected to shear stress resulting in fiber-matrix debonding. The increase in the debonding length causes an increase in the fiber pull-out length. In milling, not all the new surfaces created by tool-workpiece engagement become the machined surface. However, during this process, the strain energy absorbed by the deformed matrix is released into fiber-matrix debonding along the fibers which can cause fiber pull-out on the machined surface. In this study, shear strain energy of polymer matrix due to fiber bending during milling tool-workpiece engagement was calculated with the geometrical relationship between fibers and a cutting edge. We found that the increase in Ra and Rz of the machined surface had clear tendencies to the increase in the calculated energy.

Effect of steel fiber-volume fraction and distribution on flexural behavior of Ultra-high performance fiber reinforced concrete by digital image correlation technique

This paper investigated the effect of steel fiber-volume fraction (0.5%, 1.0%, 1.5%, and 2.0%) and distribution on the flexural behavior of ultra-high performance fiber reinforced concrete (UHPFRC). Digital image correlation (DIC) was used to obtain the crack propagation behavior of UHPFRC under bending load. With increasing fiber-volume fraction, the crack-propagation path becomes more zigzagged. Based on the flexural response of UHPFRC and fiber distribution on the crack plane, a correlation between fiber distribution characteristics and flexural behavior was discussed. The fibers number per unit area for S0.5, S1.0, S1.5, and S2.0 were 7, 14, 21, and 31, respectively. The fiber pull-out length in cracked zone with different fiber-volume fractions was about 3.56 mm. The fiber orientation factor (ηθ) of S0.5, S1.0, S1.5, and S2.0 were 0.80, 0.79, 0.69 and 0.61 respectively. A quadratic relationship between the ηθ and the fiber pull-out number is proposed. The flexural-tensile strength ratio (β) is about 2.52 for UHPFRC exhibiting deflection hardening behavior. Finally, the post-cracking tensile behavior of UHPFRC was analyzed based on the matrix softening and fiber bridging curve models by the inverse analysis method. The tension softening curves obtained from the tri-linear softening curve analysis exhibited good agreement with the experimental results.

Thermomechanical fatigue behaviors and failure mechanism of 2.5D shallow curve-link-shaped woven composites

Thermomechanical fatigue (TMF) performance is one of the most challenges for aero-engine materials. This work experimentally elaborated the in-of-phase (IP) TMF behaviors and failure mechanism of high-temperature resistant 2.5D woven composites (2.5DWCs) for the first time. In this study, both fatigue load and thermal load varying from 160 °C to 260 °C are synchronously imported in the form of trapezoidal wave. An experimental platform consisting of quasi-static mechanical tester, strain collection device, heating/cooling equipment and temperature control system was firstly established. The relationship between stress level and TMF life was obtained. The fracture morphologies were investigated using scanning electron microscope (SEM) and X-ray computed tomography (Micro-CT). Results show that the TMF behaviors of 2.5DWC exhibit a low cycle fatigue characterization with a fatigue limit of 0.75 stress level. The hysteresis loops gradually shift to the right, confirming an elongation of specimen during the TMF. It indicates a reduction of inclination angle of warp yarns. Particularly, the failure behavior is fiber-dominated brittle fracture mode, without clear necking phenomenon. The fiber pull-out length and the extensive debonding are more severe than those failed in the static loading. Finally, a probable failure mechanism for the TMF behaviors of 2.5DWC is proposed.

Magnetic resonance imaging analysis of screw in-type lateral anchor pull-out in large to massive rotator cuff repair in patients older than 60 years.

BackgroundThis study was performed to identify the incidence of screw in-type lateral anchor pull-out in patients older than 60 years who underwent rotator cuff repair for large to massive rotator cuff tear (RCT).MethodsWe reviewed 25 patients over 60 who were diagnosed with large to massive RCT and underwent arthroscopic rotator cuff repair in our hospital from March 2017 to February 2021. Preoperative tear size (anterior to posterior, medial to lateral) was measured via preoperative magnetic resonance imaging (MRI). All 25 patients underwent MRI scanning on postoperative day 1 and at 3 months after surgery. The change of anchor position was measured in axial views on MRI images postoperative day 1 and 3 months after surgery. And it was statistically compared according to bone mineral density (BMD), sex, and number of lateral anchors.ResultsTwo MRIs (postoperative day 1 and 3 months) in 25 patients were compared. Anchor pull-out occurred in six patients during 3 months (6.7%), and the mean pull-out length difference was 1.56 mm (range, 0.16–2.58). There was no significant difference in the number of pull-out anchors, degree of pull-out difference by comparing BMD (A, BMD≤-2.5; B, BMD>-2.5), sex, or number of anchors used in each surgery (C, two anchors; D, three anchors) (p>0.05).ConclusionsPull-out of screw in-type anchors was rarely observed and the mean pull-out length difference was negligibly small in our study. The screw in-type lateral anchor seems to be a decent option without concern of anchor pull-out even in elderly patients.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Surface morphology on carbon fiber composites by rotary ultrasonic milling

Carbon-carbon composites (C/C composites) is typical high temperature resistant material. Therefore it is applied in solid rocket motor (SRM) throat mostly. Because the throat is mostly single piece and mini-batch, which is not suitable for mold forming. Usually, numerical control machining is still the main method. Due to high strength and heterogeneous composites, the machining damage defects are obvious and quality is poor. Thus, from the perspective of C/C composites ablation resistance, rotary ultrasonic machining technology effect on C/C composites surface defects and damage is investigated. Moreover, the influence of ultrasonic vibration on fiber cutting angle and machined surface morphology is analyzed. Meanwhile, based on comparative experiment, fiber pull-out length and surface porosity are presented as characterization parameters. The results show that ultrasonic vibration not only improves fiber cutting angle effectively, but also reduces pores and cracks on machined surfaces. Moreover, it reduces fiber pull-out length by 10%–50% numerically when along fiber milling. When fiber is perpendicular to the cutting direction, the pull-out length becomes shorter. The above study provides a theoretical basis for subsequent machined damage influence on ablation resistance of C/C throat.

Dynamic triaxial compressive response and failure mechanism of basalt fibre-reinforced coral concrete

The dynamic triaxial mechanical properties of basalt fibre-reinforced coral aggregate concrete (BFRCAC) were studied using the split Hopkinson pressure bar device with an active confining. The results revealed that the dynamic triaxial compressive strength and dynamic triaxial elastic modulus of BFRCAC increase with an increase in strain rate and confining pressure. The increase in confining pressure reduces the strain rate effect of the dynamic triaxial compressive strength and dynamic triaxial elastic modulus, and the increase in strain rate reduces the confining pressure effect of the dynamic triaxial compressive strength and dynamic triaxial elastic modulus. Furthermore, the critical strain of BFRCAC increases with an increase in the strain rate but decreases with an increase in the confining pressure. The confining pressure reduces the damage degree of BFRCAC; as a result, the failure mode of BFRCAC changes from longitudinal splitting failure to shear failure. The increase in the confining pressure and strain rate reduces the pull-out length of basalt fibre (BF). The addition of BF improves the strain rate effect of the dynamic mechanical properties of coral aggregate concrete (CAC), reduces the failure degree of CAC, and increases the shear failure characteristics of CAC.