Higher Ultimate Strength Research Articles

The effect of bamboo (Phyllostachys pubescens) cell types on the structure of hemicelluloses

Bamboo ( Phyllostachys pubescens ) is a promising high-performance material because of its large planting areas, fast growth, good adaptability, high ultimate strength and stiffness. Hemicelluloses in bamboo have been focused and studied, however, less effort has been dedicated to study on the components, distributions and structures of hemicelluloses in different cells for explaining the mechanism of bamboo growth. Here, we obtained dimethyl sulfoxide (DMSO)-soluble and alkali (NaOH)-soluble hemicelluloses from bamboo fibers (BF) and parenchyma cells (PC), which were separated from bamboo ( Phyllostachys pubescens ) by their density difference. Molecular weight analysis revealed that the molecular weights of DMSO-soluble and alkali-soluble hemicelluloses isolated from PC were higher than those isolated from BF. Chemical compositions and cell morphology was characterized by field emission scanning electron microscope (FE-SEM), high-performance anion exchange chromatography (HPAEC), and confocal Raman microscope (CRM). The results showed that the content of cellulose (36.32 %) was higher in BF with thicker wall, while the content of lignin and hemicelluloses (36.33 % and 19.39 %, respectively) was higher in PC with thinner wall. The Fourier transform infrared (FT-IR) spectra and nuclear magnetic resonance (NMR) technique analyses indicated that bamboo hemicelluloses were composed of O -acetyl- α - L -arabino-4- O -methylglucurono- β -(1→4)- D -xylan and β -(1→3) (1→4)-glucan. 1 H NMR showed that the acetylation degree of H D -Fiber (0.069) was lower than that of H D -Parenchyma (0.127). Particularly, the hemicelluloses isolated from BF were acetylated only on C3 position, while hemicelluloses isolated from PC were acetylated both on C2 and C3 positions. This work presents a novel understanding about hemicelluloses structures of different cell types in bamboo and holds promises for the high-value added utilization of bamboo in the fields of food-related productions and biorefinery. • Hemicelluloses isolated from bamboo fibers and parenchyma cells were firstly investigated. • Hemicelluloses from parenchyma cells were acetylated on C2 and C3 position. • Hemicelluloses from bamboo fibers were acetylated only on C3 position. • The major structure of hemicelluloses is O -acetyl- α - L -arabino-4- O -methylglucurono-(1→4)- β - D -xylan. • The second major structure of hemicelluloses is β -(1→3) (1→4)-glucan.

Microstructure and mechanical properties of Ta–Ti alloy by plasma-activated sintering

Tantalum-based alloys have developed rapidly in the fields of aerospace, nuclear industry, weapons, and national defense heavy industries due to their high melting point, low ductility-brittle transition temperature, and well ductility. However, pure tantalum exhibits low room-temperature strength and intergranular fracture, which is attributable to its strong adsorption to interstitial oxygen during sintering. In this work, high-strength Ta–Ti alloy is achieved by introducing Ti to consume oxygen by forming TiO2 and inhabiting the solution of oxygen in Ta alloys. The Ta–Ti alloys mainly consist of dense Ta matrix and dispersed TiO2 second phase. With the addition of 2 wt% Ti, the Ta–Ti alloy with high densification of 99.2% not only exhibits high ultimate bending strength of 1345 MPa from dispersion strengthening by TiO2 oxides, but also has good plasticity of 6% with a transgranular fracture and numerous dimple. The present work may facilitate the development and industrial application of Ta-based alloys.

Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.

A new approach to improve strength and ductility of laser powder deposited Inconel 718 thin-wall structure

Laser powder deposition of Inconel 718 superalloy has been considered as a promising technique for the restoration of damaged aerospace components. A novel gradient laser power (GLP) deposition method is proposed to build Inconel 718 thin-wall structures by gradually reducing laser powers. The method not only alleviates micro-segregation but also tunes detrimental Laves phases’ content, size and morphology by controlling the solidification conditions. Macroscopic features, geometrical characteristics (layer widths and layer heights), porosity, tailored microstructure, microhardness and room temperature tensile properties are systematically investigated. A unique microstructure containing discrete fine Laves phases and a mixture of equiaxed grains and fine columnar grains with no obvious texture is obtained in GLP samples due to the enhanced cooling process and multidirectional heat flux. The relationships among processing parameter, microstructure and mechanical properties are discussed in detail. Compared with samples deposited by the conventional constant laser power (CLP) deposition method, GLP samples exhibit an excellent combination of strength and ductility with considerable yield strength, high ultimate strength, prominent strain hardening exponent and superior ductility of 40%. The GLP method provides a useful strategy to tailor microstructures and improve mechanical properties by purposely manipulating processing parameters.

Composition inhomogeneity reduces cracking susceptibility in additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy produced by laser powder bed fusion

Pre-alloyed and blended powders are frequently used feedstock options for additive manufacturing; however, nanoscale compositional inhomogeneities induced by blended powders are often ignored. This composition inhomogeneity is more pronounced in eutectic high-entropy alloys (HEAs) with small solidification ranges and sluggish diffusion effects. In this study, AlCoCrFeNi 2.1 eutectic HEAs were prepared by laser powder bed fusion (LPBF) using both pre-alloyed and blended powders. The alloy built using the pre-alloyed powder (PA) exhibited cellular structures that consisted of ordered body-centered cubic (B2) cells decorated with face-centered cubic (FCC) networks. The composition inhomogeneity in the alloy built using blended powders (BP) led to lamellar structures consisting of alternate FCC and B2 lamellas. The orientation relationships between FCC and B2 in both PA and BP were determined as {110} B2 //{100} FCC , < 001 > B2 //< 011 > FCC . The fine cellular structures in PA resulted in high ultimate strength (1400 MPa) but poor ductility. Solid-state cracking and delay cracking were observed in PA. The straight and extended FCC lamella in BP provided preferential channels and long distances for dislocation slippages, which combined high strength (1200 MPa) and ductility (10%). The improved deformation ability of BP enabled a strain-tolerant microstructure and eliminated the solid-state and delay cracking in as-built LPBF AlCoCrFeNi 2.1 alloys. • AlCoCrFeNi2.1 HEAs were additive manufactured by pre-alloyed and blended powders, respectively. • Cellular structures consisting of B2 cells and FCC networks were associated with cracks. • Lamellar B2/FCC structures resulted in an excellent combination of strength and ductility. • Composition inhomogeneity produced by blended powders eliminated cracks.

A strong ferritic high‐resistivity multicomponent alloy with tunable ordered coherent multicomponent nanoprecipitates

We design and investigate a ferritic multicomponent alloy with high electrical resistivity, low temperature coefficient of resistivity (TCR) in a wide-temperature range, high strength, and moderate deformability, aiming to overcome the bottlenecks limiting the development of cost-efficient high-quality resistors. The developed bulk alloy with nominal composition Fe55Cr28Al12Ti3Si2 (at. %) shows a body centered cubic (BCC) matrix phase embedded with ordered coherent multicomponent nanoprecipitates in as-cast condition, which enables a high resistivity of 183 µΩ·cm, a low TCR of -35 ppm/K (from 298 to 673 K), a high yield strength of 1055 MPa, a high ultimate compressive strength of 1980 MPa and a moderate uniform compressive strain of 33% (at 673 K). The fully coherent and ordered multicomponent L21 nanoprecipitates in the BCC-α matrix enhance the stress required for dislocation propagation, leading to the improved strength and work hardening ability, according to the comparative study on the alloy variants with and without nanoprecipitates. Also, the multicomponent L21 nanoprecipitates enable the effective tuning of Kondo-like scattering and contribute to the low TCR of the material. The work thus demonstrates a design strategy for low-cost precision resistance alloys to achieve high and stable resistivity in wide temperature ranges combined with high strength and moderate compressive deformability by introducing well-tuned ordered coherent multicomponent precipitates in multicomponent alloy systems.

Solidification characteristics and high temperature tensile properties of Ni-based superalloy IN713C

The solidification characteristics and high temperature tensile properties of IN713C superalloy were investigated using directional solidification methods at withdrawal rates of 10, 50 and 100 µm/s, respectively. The results show that carbide morphologies change from block and long strip to short rod and granular with increasing withdrawal rate. The increase of withdrawal rate promotes the microsegregation of Mo, Nb and Zr, and contributes to precipitation of the γ/γ’ eutectic and boride. With the withdrawal rate increasing from 10 µm/s to 50 µm/s, the high temperature yield strength, ultimate strength and elongation of the IN713C alloy increased by 11.8%, 18.3% and 64% respectively. The increase of the γ/γ’ eutectic and boride lead to slight decrease in strength when the withdrawal rate increased from 50 µm/s to 100 µm/s. The fractographic observation of tensile specimen indicates that the integrate carbide particles are an overwhelming majority at a higher withdrawal rate. When the withdrawal rate decreases, the particles become larger and more secondary cracks are generated. The morphology of carbides affects the tensile fracture mechanism of the alloy. With the decrease of carbide size, the crack source of the IN713C alloy changed from brittle carbides to the interface between carbide and matrix.

Nano-TiB whiskers reinforced Ti–6Al–4 V matrix composite fabricated by direct laser deposition: Microstructure and mechanical properties

Titanium matrix composites (TMCs) have attracted widespread research interest due to their excellent properties. Herein, TMC reinforced with quasi-continuous reticular nano-TiB whiskers (nano-TiBw) was fabricated via a direct laser deposition method. The network of TiB reinforcements was found to be equiaxial and dendritic, and the addition of boron was shown to be beneficial to the equiaxial transition and refinement of α grains. The interface between the nano-TiBw and Ti64 matrix was observed to be clean and flat. The microhardness of the TMC was 465.1 HV0.025, 31% higher than that of the Ti64 alloy. Compressive tests showed that the TMC exhibited high ultimate compressive strength and good plasticity due to the grain refinement of the matrix and load transfer effect of nano-TiBw. The lower friction coefficients, smaller wear tracks, and minor wear weight loss revealed the superior wear resistance of the TMC in comparison to that of the Ti64 alloy. The reticular TiBw was found to be responsible for reducing the sensitivity of the TMC to adhesive wear.

The Shearing Behavior of Nanowire Contact Pairs in Air and the Role of Humidity

A new technique based on optical microscope nanomanipulation is developed to permit optical observation of the shearing process between cantilevered nanowires (NWs). Real‐time observation of the deflection shape of NWs during shearing under controlled environmental conditions enables their shear stress evolution to be evaluated with respect to relative humidity (RH). The average static and kinetic shear strengths, and MPa, are found to be insensitive to the RH within the range of 40–60%. When the RH increased to 74%, the shear strength values increase to and MPa. When the RH decreases to 20%, a dramatic increase in the static and kinetic shear strengths is observed: and MPa. Water films absorbed on the surface of NWs within the RH range of 40–60% can lubricate their frictional interface and thus dramatically decrease the shear strength. At high RH of above , the viscous effects of a water meniscus condensed around the contact point between two NWs can significantly enhance the shear strength and dampen stick‐slip behavior. The detachment of two NWs is then controlled by the rupture of a meniscus bridge, leading to high ultimate shear strength value of several tens of MPa.

Failure Modes of RC Structural Elements and Masonry Members Retrofitted with Fabric-Reinforced Cementitious Matrix (FRCM) System: A Review

Much research has been conducted and published on the examination of the behavior of reinforced steel and concrete structures with a FRP system. Nevertheless, the performance of FRP differs from that of FRCM, particularly at high temperature and ultimate strength. The present study provides a review of previous research on structural elements (viz. beams, columns, arches, slabs, and walls) retrofitted with FRCM systems, taking account of various parameters, such as layers, composite types, configurations, and anchors for controlling or delaying failure modes (FMs). Additionally, this paper discussed the details of different FMs observed during experimental tests, such as crushed concrete or bricks, fiber debonding from substrate materials, slippage, fiber rupture, and telescopic failure for strengthened specimens. Moreover, this paper investigated where and how fractures may develop in structural elements retrofitted with the FRCM system under various retrofit scenarios. To this end, in addition to the review of the relevant literature, a large dataset has been compiled from different (RC) structural elements and masonry members. Next, a relationship is developed between failure modes (FMS) and influential parameters, i.e., the number of layers and the type of composite, based on this dataset. This can be used as a benchmark example in future studies, as there is no such basis available in the literature, to the best of the authors’ knowledge.

In-situ synchrotron diffraction study on compressive deformation behavior of Mg92Y5Ni3 alloy mostly composed of LPSO

The compressive deformation behavior of the as-cast and as-extruded Mg92Y5Ni3 (at.%) alloy mostly composed of long period stacking ordered (LPSO) phase was studied by in-situ synchrotron radiation combined with the analysis of deformation traces after compression at different applied stress. The as-cast alloy has random texture, while the as-extruded alloy has a typical basal texture with basal plane parallel to extrusion (compression) direction. Prior to macro-yielding, some softly oriented grains are preferentially plastically deformed, leading to micro-yielding. The micro-yielding behavior of both as-cast and as-extruded alloys is controlled by basal slip, the as-extruded alloy has higher micro-yielding strength than the as-cast alloy. The activated deformation mode near the macro-yielding point is prismatic slip in both as-cast and as-extruded alloys, and as the hard oriented grains dominate in the as-extruded alloy, the compressive yield strength of the alloy is increased from 217 MPa to 535 MPa after extrusion. The kinking activated following the prismatic slip can introduce a large number of dislocations in the as-extruded alloy, resulting in high strain-hardening rate of 3000 MPa, high ultimate compressive strength of ∼800 MPa and plastic strains above 10%.

Improving the mechanical properties of polycaprolactone using functionalized nanofibrillated bacterial cellulose with high dispersibility and long fiber length as a reinforcement material

Nanofibrillated bacterial cellulose (NFBC) produced in the presence of hydroxypropylcellulose (HPC) (HP-NFBC) is amphiphilic and has a very long fiber length (>15 μm). In this study, polycaprolactone (PCL)-grafted HP-NFBC (HPNFBC-g-PCL) was prepared via ring-opening polymerization from the hydroxy groups on the HP-NFBC surface as initiation sites. The mechanical properties of the nanocomposites containing PCL homopolymer and HPNFBC-g-PCL were investigated. The nanocomposite with 13 wt% cellulose was the stiffest film with the highest ultimate strength and Young’s modulus of 57.3 and 661.3 MPa, respectively. HP-NFBCs grafted with PCL of different molecular weights (20, 15, and 9 k) were also prepared to study the effect of the graft length on the mechanical properties of the nanocomposites. Grafting HP-NFBC with a higher molecular weight (20 k) PCL led to an enhanced ultimate strength and Young’s modulus. These results suggest that HP-NFBC can serve as an excellent reinforcement material.

Structural Performance of Different Forms of Corrugated Plate Shear Walls under Dynamic Loading

Steel plate shear wall systems are currently utilized in resisting seismic loading in multistory buildings within seismic prone regions. They consist of infill plates that are bounded by a surrounding frame. Nonlinear push over and cyclic analyses were carried out to study different forms and configurations of horizontal trapezoidal corrugated steel plate shear walls, namely singly corrugated, doubly corrugated as well as perforated corrugated steel plate shear walls. A finite element model was developed for a horizontal trapezoidal corrugated steel single plate shear wall (OPSW) using Abaqus software. It was validated. Thereafter, while maintaining the original overall properties, a parametric study was carried out to investigate the effect of changing plate thickness, plate width/height ratio, deeper corrugations, providing double plates, as well as perforations on the seismic behavior of steel plate shear walls. The paper aims at achieving a better understanding of the main parameters that control the optimum performance of the horizontal trapezoidal corrugated steel shear walls. Few studies have discussed this matter, so the current study comes to fill the gap. It is concluded that double horizontal trapezoidal corrugated plate shear walls (DPSW) are very efficient shear wall systems. They experience stable hysteretic cyclic loops. They have higher shear stiffness, higher buckling load, and higher ultimate strength as well as higher residual strength than OPSW. They also experience higher ductility and more energy dissipation compared to OPSW. Perforations were found to reduce the contribution of the corrugated plate shear wall in resisting the seismic forces, as well as the subsequent reduction of the wall strength and stiffness.

Production of transverse magnetic field annealed brass band and how the production process influences the mechanical properties, as well as their correlation and compliance

This paper examines the effect of the thickness h, the deformation reached during the last cold rolling operation&nbsp;&epsilon; and the final normalized annealing mode v on the mechanical properties of brass band. The paper looks at the correlation between the ultimate strength &sigma;в, elongation and hardness HV in terms of their meeting the specification. The production of L68 brass band involved semi-continuous casting, hot rolling to the thickness of 6 mm and cold rolling to h = ~0.56&ndash;0.96 mm with intermediate annealing at H = 1.5&ndash;2.7 mm ensuring the deformation&nbsp;&epsilon; within 62 to 72%. The intermediate and final continuous annealing lines are equipped with three-phase TFIH (Transverse Flux Induction Heating) units. An intermediate annealing mode has been established that ensures the grain size of 40&ndash;80 &mu;m. The strip travel speed was varied as follows during final annealing: &nu;&nbsp;= 30&ndash;46 m/min. The authors determined the stochastic dependences of the properties on&nbsp;&nu; , h and &epsilon;, as well as the annealing modes that are necessary to achieve each property. Actual correlations HV(&sigma;в), &delta;(&sigma;в) within the specified ranges were considered versus the properties of the band produced by deformation. It was established that the cold rolling process, together with the heat treatment mode, has an effect on the properties of annealed band and, vice versa, on the heat treatment mode that is necessary to achieve the required properties. With hardness being the same, the induction heat annealed brass band has a higher ultimate strength в than the band produced by normalized final deformation. As a result, the linear relationship &sigma;в = f(HV) of the rolled band produced by normalized final annealing is shifted in relation to the optimum position of such relationship within the specified limits adopted in the period when the rolled band was exclusively produced by final deformation. Consequently, the final annealing mode ranges that are necessary for achieving certain properties within the specified ranges, do not match, thus making the task of having the resulting properties hit the above ranges more challenging. Thus, it is proposed to use online control and annealing control to eliminate rejects, and to use the annealing mode-required property relationships obtained from the given data for setting up the initial process mode.

Interfacial shear and flexural performances of steel–precast UHPC composite beams: Full-depth slabs with studs vs. demountable slabs with bolts

Two types of steel–precast ultra-high-performance concrete (UHPC) composite beams were investigated in this study, which can be vastly used in accelerated bridge construction (ABC). One of them contains full-depth slabs with stud shear connectors embedded in shear pockets, while the remaining one adopts demountable slabs with high-strength friction-grip bolts (HSFGBs). Four-point bending tests were conducted on six large-scale composite beams to investigate the interfacial shear and flexural performance of such innovative types of steel–precast UHPC composite structures. The failure modes, vertical deflection, horizontal interfacial slip and the stain distribution at mid-span cross-section were investigated. The experimental results indicated that the cracking patterns and failure modes of the composite beams were highly dependent on the slab concrete types and the degrees of shear connection. The composite beams adopting UHPC slabs achieved larger cracking resistance and higher ultimate strength than those containing normal-strength concrete slabs and favorable ductility. Similar trends were also presented by the composite beams with large degrees of shear connection. The composite beams with HSFGBs showed enhanced load capacities and larger vertical deflections and horizontal interface slips at peak load than those adopting stud shear connectors. Additionally, the composite beams that failed in shear connector fractures presented shear resistance–interface slip relationships comparable to their push-out counterparts. Finally, theoretical formulas based on rigid plastic analysis were proposed for predicting the flexural capacity of both types of composite beams.

Effect of chromium addition on the copper binder structure, properties and adhesion to diamond

The study covers the effect of chromium on the structure, mechanical properties, and adhesion of alloys used as a binder for metal-diamond composites. Cu–Cr powder mixtures were obtained by high-energy ball milling in a planetary centrifugal mill. This process was used to obtain two-phase Cu–Cr powders with uniformly distributed submicron Cr particles. Cu–Х%Cr compact samples (where Х = 10, 30 and 50 %) were obtained by hot pressing. It was found that Cu–30%Cr compact samples showed the best mechanical properties (9 times higher as compared to pure copper). These alloys feature a hardening mechanism based on the Hall–Petch law. The resulting alloys have a homogenous ultrafine structure, which results in high ultimate bending strength (2330 MPa). Chromium addition to the copper binder considerably increases its adhesion to diamond in metal-diamond composites due to chemical interaction between chromium included into the binder and diamond carbon with Cr3C2 carbide formation.

Structure, Morphology, and Permeability of Cellulose Films.

The work is focused on the study of the influence of the cellulose type and processing parameters on the structure, morphology, and permeability of cellulose films. The free volume of the cellulose films was evaluated by the sorption of n-decane, which is a non-solvent for cellulose. The structural features of the membranes and their morphology were studied using X-ray diffraction, IR spectroscopy, SEM, and AFM methods. The characteristic features of the porous structure and properties of cellulose films regenerated from cellulose solutions in the N-methylmorpholine-N-oxide (NMMO) and cellophane films were compared. Generally, cellulose films obtained from solutions in NMMO have a higher permeability and a lower rejection (as measured using Orange II dye) as compared to cellophane films. It was also found that the cellulose films have a higher ultimate strength and modulus, whereas the cellophane films are characterized by higher elongation at break.

Regulating the Tensile Properties of a Nano‐Lamellar Austenitic Stainless Steel via Cryogenic Electropulsing

Electropulsing treatment (EPT) in the liquid nitrogen (LN) circumstances, referred to as LN‐EPT, is utilized to regulate the microstructure and tensile properties of a cold‐rolled 316L austenitic stainless steel. The electropulsing effects between the samples treated in the ambient environment at room temperature (RT) and in the LN temperature are compared. The results confirm that the LN‐EPT‐processed samples can also realize a fully recrystallized microstructure, and even the Joule heat is significantly suppressed compared with the RT‐EPT samples. The tensile properties of the LN‐EPT samples show both higher yield strength and higher ultimate strength while keeping considerable elongations compared with the RT‐EPT samples because of the finer recrystallized structure in the LN‐EPT samples. This attempt of LN‐EPT may shed some new light on developing the cryogenic electropulsing‐assisted forming methods for metals in the future.

Composite-to-metal joining using interference fit micropins

Interference fit micropinning is a novel joining method that involves inserting thin pins with a size interference into an array of ultra-thin holes to create high strength structural joints. An experimental and finite element (FE) modelling study demonstrates the high structural properties of composite-to-metal joints using interference fit micropins. The joint studied consisted of plates of carbon-epoxy laminate and aluminium alloy joined using an array of steel micropins (505 μm diameter) with a close interference (1%) to the holes. The interference fit micropins are effective at creating composite-to-metal joints with high specific ultimate strength and ductility. The capacity of micropins to provide composite-to-metal joints with high structural properties under lap shear and peel load conditions is demonstrated. The effect of the spacing and number of micropins on the joint properties is evaluated.

Molecular-Level Elucidation of a Fracture Process in Slide-Ring Gels via Coarse-Grained Molecular Dynamics Simulations

Slide-ring (SR) gels with slidable cross-linked cyclic molecules exhibit considerably higher fracture toughness than conventional fixed cross-link (FC) gels. However, the mechanical properties of SR gels are still unsatisfactory, and thus, these gels cannot be practically applied. Therefore, molecular scale insights into the fracture mechanism of SR gels are required to improve their mechanical properties. This study conducted tensile strain simulations of FC and SR gels using a coarse-grained molecular dynamics (CGMD) method to elucidate the fracture mechanism of SR gels. The CGMD simulations showed that the SR gels exhibited higher fracture toughness than the FC gels. In the FC gels, the axis chains easily broke under a low strain because fixed cross-links constrain the polymer chain, resulting in stress concentration on the axis chains. On the contrary, in the SR gels, the axis chains did not break until a high strain was applied because the cross-linked cyclic molecules slide not to accumulate stress concentration. The analysis of the fracture mechanism of the SR gels revealed that the chain-ends are the origin of the fracture in the SR gels. The cross-linked and un-cross-linked cyclic molecules slide on the axis chains and are stacked around the chain-ends. The stacked cross-linked cyclic molecules induced stress concentrations around the chain-ends. Next, we investigated the effect of coverage on the SR gels. We found that low-coverage SR gels exhibited higher fracture toughness and ultimate strength than high-coverage SR gels because the stacked un-cross-linked cyclic molecules prevent cross-linked cyclic molecules from sliding, leading to a low fracture toughness caused by the stress concentration at the chain-ends. The axis chains of the low-coverage SR gels with a high fracture toughness deformed to the strain direction until a high strain. Thus, the low-coverage SR gels showed a high orientation toward the strain direction. A high orientation contributes to the uniform distribution of mechanical stress on the chains, leading to a high ultimate strength. Although the SR gels generally exhibit a low ultimate strength, SR gels with a low coverage ratio of 5% showed a higher ultimate strength than FC gels. Finally, we propose that, compared with the high-coverage SR gels, the low-coverage SR gels exhibit both higher fracture toughness and ultimate strength, based on the atomistic insight pertaining to the mechanism by which the low-coverage SR gels possess free space for cross-linked cyclic molecules to move to the chain-ends until a high strain is applied.