Static Flexural Strength Research Articles

Static and cyclic behavior of high-performance concrete reinforced with hybrid steel fibers using notched and un-notched flexural specimen

In this paper, the static and cyclic behavior of high-performance concrete reinforced with hybrid steel fibers (HPFRCs) using notched and un-notched flexural specimen were experimentally studied. The term 'hybrid steel fibers' refers to using a combination of different steel fiber s in HPFRC mortar. Three HPFRC types, produced from an identical mortar, contained a same total fiber content of 2.0 vol% but different hybrid fiber systems as follows: 0.5, 1.0, 1.5 vol% long hooked fiber blended with 1.5, 1.0, 0.5 vol% short smooth, respectively. All flexural specimens were designed with a prism-shape having dimensions of 40 × 40 × 160 mm (width × depth × full length). Two specimen types were employed: un-notched and notched specimen with its depth of 5 mm at specimen bottom. The specimens were experimented under static and cyclic loading using a three-point bending test. Despite the lower peak static load, the notched specimen produced the higher flexural strength and critical stress intensity factor, regardless of the HPFRC types. Under cyclic loading, the number of cycles of the notched specimens showed lower than that of the un-notched specimens, for all the HPFRC types at same fatigue stress ratio. Besides, the higher static flexural strength seemed to produce the lower fatigue endurance limit, based on the proposed fatigue response curves built by regression technique.

Zirconia specimens printed by vat photopolymerization: Mechanical properties, fatigue properties, and fractography analysis.

The mechanical and fatigue properties of zirconia specimens printed by vat photopolymerization (VPP) were evaluated and compared with those of zirconia specimens milled by computer numerical control (CNC). Bar-shaped specimens were printed by stereolithography (SL) and digital light processing (DLP). CNC-milled specimens were used as control samples. The fracture toughness, hardness, and flexural strength properties of the zirconia specimens were evaluated via single edge V-notch beam tests, Vickers hardness tests, and 3-point bending tests. Dynamic fatigue tests were carried out in distilled water using a step-stress test. After static bending and dynamic step-stress testing, fractography analysis was performed. Statistical analysis was carried out to compare the fracture toughness, hardness, flexural strength, and fatigue cycle results of each group (α = 0.05). The fracture toughness values did not significantly differ among the groups (p>0.05). The flexural strength was 894.10MPa for SL, 831.46MPa for DLP, and 1140.39MPa for CNC. The flexural strength of CNC was greater than that of SL and DLP (p<0.01). The mean fatigue cycles were 23498.07 for SL, 19858.60 for DLP, and 31566.80 for CNC. The mean fatigue failure strength was 643.13MPa for SL, 530.63MPa for DLP, and 903.75MPa for CNC. The fatigue failure strength of CNC was greater than that of SL and DLP (p<0.05). Fractography analysis revealed material defects at the fracture origin for each group. A partially fused structure of the incompletely debonded resin could be observed in SL, and a porous region of incompletely sintered zirconia grains could be observed in CNC. The fracture toughness and hardness of zirconia printed by VPP are comparable to those of zirconia milled by CNC. However, zirconia milled by CNC has superior static flexural strength and dynamic fatigue resistance. Further studies are needed to explore the clinical applications of VPP-printed zirconia.

Investigation of Static Flexural Strength of Aluminium Honeycomb Panels with Varying Cell Sizes

Investigation of Static Flexural Strength of Aluminium Honeycomb Panels with Varying Cell Sizes

A bionic strong nanostructured soy protein-based adhesive enabled antistatic and self-extinguishing wood-based composites

Wood composites represent one kind of sustainable functional materials for interior decoration and packaging, but their tendency to generate static electricity poses discomfort and potential fire hazards. To address this huge challenge, we herein report a strong, conductive, nanostructured formaldehyde-free soy protein-based adhesive by mixing nanocellulose and tannic acid functionalized MXene, and soy protein, which is then used to create antistatic and fire-extinguishing wood composites. The resulted soy protein-based adhesive exhibited an exceptional bonding capability due to its bionic organic-inorganic hybridized crosslinking structure. With this soy protein-based adhesive, as-prepared wood composites achieved a static flexural strength of 14.08 MPa, meeting the demanding interior use requirement. Because of the presence of both MXene and quaternary ammonium salt in the adhesive, the resultant wood composite shows an electrical resistance of 3.123 × 109 Ω·cm, satisfying the antistatic requirements for wood-based composites, and a desired self-extinguishing ability. This work offers a promising strategy to create strong nanostructured bio-adhesive, which can be used for producing multifunctional wood composites as decoration and packaging materials.

Flexural fatigue behavior of ultra-high performance concrete under low temperatures

Ultra-high performance concrete (UHPC) shows superior mechanical performance, which leads to increasing applications in infrastructure constructions that are subjected to different loading (i.e., flexure, tension, compression, etc.) and environmental conditions (ambient, freeze, etc.). Among them, the flexural performance of UHPC under low temperatures (i.e., sub-zero temperature) is still little understood especially under fatigue loading. To investigate the flexural fatigue properties of UHPC under low temperatures, eleven UHPC prisms are subjected to cyclic bending at different stress levels from 0.40 to 0.80 (the ratio between applied maximum fatigue stress and static flexural strength) and temperatures of 20 °C, -10 °C, and -20 °C. Results indicate that the fracture interfaces for specimens under static and fatigue loading exhibit distinct differences. No fiber buckling appears for the monotonically-loaded specimens, while for specimens under fatigue loading, fibers buckled and fractured. Low temperature improves the mechanical properties of UHPC under monotonic loading due to enhanced matrix strength. Conversely, low temperature adversely affects the flexural fatigue performance of UHPC due to the cold brittleness nature of matrix and steel fibers, leading to the accumulation of matrix deterioration and the fracture of steel fiber. When the temperature drops from 20 °C to -10 °C and -20 °C, there is a 15.0 % and 12.7 % decline in the flexural fatigue strength of UHPC, respectively. In addition, low temperature accelerates the degradation of UHPC, resulting in a larger and faster accumulation of fatigue deformation, including tensile strain, mid-span deflection, and fatigue deformation modulus.

Optimizing gypsum particleboard properties: An orthogonal analysis of pennisetum giganteum and phosphogypsum composites

Gypsum particleboard is attracting attention in the construction industry due to its excellent properties. However, the traditional raw materials for gypsum particleboard are facing a shortage of supply. In this study, we innovatively utilized bulk solid waste Phosphogypsum and Pennisetum giganteum for the first time to manufacture gypsum particleboard. This approach not only effectively addresses the issue of insufficient supply of traditional raw materials for gypsum particleboard but also provides a new pathway for the resource utilization of phosphogypsum. Through an orthogonal experimental design, we focused on optimizing the gypsum particleboard formulation, concentrating on factors such as density, the ratio of Pennisetum giganteum to gypsum (grass-plaster ratio), the ratio of water to gypsum (water-plaster ratio), and the size of the particles. The study determined that the optimal formulation parameters were a density of 1.2 g/cm³, a grass-plaster ratio of 0.20, a water-plaster ratio of 0.25, and a particle mesh number of 14. Under these conditions, the gypsum particleboard exhibited excellent performance, characterized by a static flexural strength of 6.5 MPa, a modulus of elasticity of 2010 MPa, an internal bond strength of 0.4 MPa, a 24-hour water-absorption thickness expansion rate of 2.2%, and an equilibrium moisture content of 1.6%, all meeting the American Society for Testing and Materials (ASTM) Standard D1037. These findings indicate that gypsum particleboards made with Pennisetum giganteum and phosphogypsum can perform comparably to those made with conventional materials. Additionally, a performance prediction model was established using Multiple Linear Regression Analysis (MLRA). The analysis revealed a significant linear relationship between the independent and dependent variables in the model, with the Analysis of Variance (ANOVA) significance levels being less than 0.05, demonstrating statistical significance. This result provides a theoretical basis for the future development of high-performance gypsum particleboard.

Fatigue Property Evaluation of Sustainable Porous Concrete Modified by Recycled Ground Tire Rubber/Silica Fume under Freeze-Thaw Cycles

As an environmentally friendly pavement material, porous concrete in seasonal frozen region is often subjected to repeated loads and freeze-thaw cycles. Therefore, the fatigue property of porous concrete under freeze-thaw is extremely important. However, few researches have been reported on the topic. Based on this background, this paper investigates the flexural fatigue property of ground tire rubber/silica fume composite modified porous concrete (GTR/SF-PC) with experimental and mathematical statistical methods. The flexural fatigue life of GTR/SF-PC under different freeze-thaw cycles (0, 15, 30) was tested with three-point flexural fatigue experiment at four stress levels (0.70, 0.75, 0.80, 0.85). Kaplan Meier survival analysis and Weibull model were adopted to analyze and characterize the flexural fatigue life. The fatigue life equations of GTR/SF-PC under different freeze-thaw cycles were established. The results indicate that, duo to the addition of ground tire rubber and silica fume, the static flexural strength of GTR/SF-PC is not significantly affected by freeze-thaw cycles. The flexural fatigue property of GTR/SF-PC is gradually deteriorated under the action of freeze-thaw cycles. Compared with 0 freeze-thaw cycles, the average flexural fatigue life of GTR/SF-PC decreases about 15% and the fatigue failure rate increases about 50% after 30 freeze-thaw cycles, respectively. The fatigue equations with different reliabilities of GTR/SF-PC show that the reliability is inversely proportional to fatigue life, therefore, the appropriate fatigue equation considering freeze-thaw effect is necessary for fatigue design of porous concrete.

PENGARUH POSISI SAMBUNGAN KONSTRUKSI KAYU TERHADAP DEDAIN PRODUK MEBEL BERBAHAN DASAR KAYU

Wood furniture products were one of the commodities that have a dominant contribution compared to other furniture materials to the Indonesian economy. In furniture products, the connection system was a weak point in the construction, so a detailed analysis was needed regarding the factors that affect the strength of the construction and the effectiveness of the wood connection system. The purpose of this study was to determine the quality of the wood used as outdoor chair material by carrying out several tests to obtain wood density, moisture content, MOR and MOE values and then carrying out impact tests on actual outdoor chair products. The results showed that the teak wood used in the raw material for making the product had a moisture content of 12% with an average density of 0.68 g/cm3. The results of the static flexural strength test showed that the MOE of the tested teak was 107,108 kg/cm2 and the MOR value was 1,018 kg/cm2. The compressive strength value parallel to the fiber is 536 kg/cm2. The teak sample tested was included in strong class II which is quite strong as a raw material for furniture such as outdoor chairs. Analysis of the results of the construction design found that the type of construction used was tenon mortise, cracks at the joints occurred because the tenon was too close to the head of the wood. Based on the product test results, after the product with a new construction design was made, by lowering the tenon mortise position 3 mm from the initial position. The crack that occurs in the product is caused by an error in product construction design and not from the quality of the product raw materials used.

Study on the suitability of rice straw and silicate cement

In order to study the feasibility of preparing cement particle board by compounding silicate and rice straw shavings, this paper explored their compatibility by detecting the heat of hydration of both by HPLC and characterized by FTIR, SEM and XRD. The results suggested that rice straw contained a certain amount of sugars soluble in water as well as organic carboxylic acids, having toxic effects on the hydration of silicate cement and could retard the hydration reaction of silicate cement. The addition of rice straw would inhibit the generation of crystals of hydration products in the early stage of silicate cement hydration, which makes it difficult for the C-S-H gel to build a dense spatial mesh, resulting in the poor compatibility of rice straw with silicate cement. The verification experiments exhibited that the static flexural strength of straw cement particleboard was far lower than the standard value of CB/T 24312–2009 cement particleboard, indicating that rice straw was unsuitable for direct apply for the preparation of rice straw silicate cement particleboard, and the compatibility regulation of rice straw and silicate cement was required.

Acrylic Resin Filling Cell Lumen Enabled Laminated Poplar Veneer Lumber as Structural Building Material

Wood is a viable alternative to traditional steel, cement, and concrete as a structural material for building applications, utilizing renewable resources and addressing the challenges of high energy consumption and environmental pollution in the construction industry. However, the vast supply of fast-growing poplar wood has bottlenecks in terms of low strength and dimensional stability, making it difficult to use as a structural material. An environmentally friendly acrylic resin system was designed and cured in this study to fill the poplar cell cavities, resulting in a new type of poplar laminated veneer lumber with improved mechanical strength and dimensional stability. The optimized acrylic resin system had a solid content of 25% and a curing agent content of 10% of the resin solid content. The cured filled poplar veneer gained 81.36% of its weight and had a density of 0.69 g/cm3. The static flexural strength and modulus of elasticity of the further prepared laminated veneer lumber were 123.12 MPa and 12,944.76 MPa, respectively, exceeding the highest flexural strength required for wood structural timber for construction (modulus of elasticity 12,500 MPa and static flexural strength 35 MPa). Its tensile strength, impact toughness, hardness, attrition value, water absorption, water absorption thickness expansion, and water absorption width expansion were 58.81%, 19.50%, 419.18%, 76.83%, 44.38%, 13.90%, and 37.60% higher than untreated laminated veneer lumber, demonstrating improved mechanical strength and dimensional stability, significantly. This method provides a novel approach to encouraging the use of low-value-added poplar wood in high-value-added structural building material applications.

Effects of stitching yarn types on flexural fatigue properties of 3D stitched carbon fiber composites

This work investigated the static bending and flexural fatigue properties of 3D stitched composites with different stitching yarns. The carbon and PBO fibers were adopted to reveal the effects of stitching yarn types on the fatigue characteristics and failure propagation of 3D stitched composites at low-stress levels by a high-speed camera. The results show that different stitching yarn types affected the static flexural strength of 3D stitched composites but did not affect their modulus. In addition, different stitching yarn types changed the fatigue failure mechanism of 3D stitched composites. The fatigue life of 3D stitched composites can be effectively improved by using PBO fibers since the PBO fiber can effectively delay shear crack growth and prolong the period of the catastrophic failure stage. This work proposed a new scheme for improving the mechanical properties of stitched composites.

Synergy in Flexure of High-Performance Fiber-Reinforced Concrete with Hybrid Steel Fibers

In this paper, the synergistic flexural behaviors of high-performance fiber-reinforced concrete (HPFRC) under static and cyclic loading were experimentally investigated. The HPFRCs were composed of an identical mortar matrix but different embedded fiber types and contents as follows: HPFRC0 (no fiber, 0.0% by volume), HPFRC1 (macro steel fiber, 1.5% by volume), HPFRC2 (micro steel fiber, 1.5% by volume), and HPFRC3 (hybrid fiber, 1.0% by volume macro steel fiber blended with 0.5% by volume micro steel fiber). All flexural specimens with the dimensions of 40×40×160 mm were tested under static and cyclic loading using a three-point bending fixture. The HPFRCs with embedded fibers demonstrated the clear enhancements in static flexural resistances of up to 3.54 times higher in flexural strength and 2.16 times higher in deflection capacity in comparison with the plain HPFRC. Under cyclic loading, the fatigue stress ratio, defined as the ratio of the fatigue stress amplitude to the static flexural strength, was changed to perform the fatigue behaviors of the HPFRCs. The endurance limits of the HPFRCs were observed more than 10,000 cycles at the fatigue stress ratio of 0.15, and exceeded 1,000 cycles at the fatigue stress ratio of 0.5. The order of the HPFRC series in terms of static flexural strength, static deflection capacity and fatigue life at the stress amplitudes more than 5 MPa were as follows: HPFRC3 > HPFRC2 > HPFRC1 > HPFRC0. A synergy behavior of the HPFRCs was observed for static flexural strength, static deflection capacity, and fatigue life with the stress amplitude more than 5 MPa. In addition, two models of the fatigue responses of the HPFRCs were built to predict the fatigue life of the HPFRCs according to applied cyclic load.

Investigation into the effects of various processing treatments on the flexural performance of carbon fiber reinforced polymer-bamboo scrimber composites

ABSTRACT Carbon fiber-reinforced polymer (CFRP) laminates can significantly improve the flexural performance of the bamboo scrimber. This study evaluated the effects of three fabrication methods (one-time hot pressing, secondary hot pressing, and secondary cold pressing) on the flexural performance of CFRP-bamboo scrimber composites. Four-point bending experiments and theoretical analysis were conducted to study the failure modes, flexural performance, load-displacement relationships and strain curves over time of CFRP-bamboo scrimber composites. Besides a theoretical model was proposed to describe the flexural stiffness of CFRP-bamboo scrimber composites. The results indicated that the CFRP-bamboo scrimber composite specimens demonstrated four failure modes depending on the treatment methods. Overall, the static flexural modulus of the one-time hot pressed specimens was superior (up to 1.93 times that of the untreated bamboo scrimber specimen), and the static flexural strength of the secondary cold pressing specimens was superior (up to 3.58 times greater than that of the untreated bamboo scrimber specimen), although neither the static flexural modulus nor the static flexural strength of the secondary hot pressing specimens was satisfactory. Finally, it was illustrated that the theoretical models, established to describe the load-displacement, could accurately predict the experimental results.

Rotational flexural strength of cylindrical brittle specimens

AbstractConventional static flexural strength testing of brittle cylindrical rods only subjects a small fraction of the entire specimen's area or volume to the maximum tensile stress. Thus, a nonconservative measured strength likely results since most flaws on the surface or in the bulk are not subjected to a sufficiently high tensile stress that can cause fracture. To mitigate this, a rotational flexural tester and corresponding test method were developed whereby rotation and monotonically increasing three‐point flexure were superimposed to investigate fracture response of solid glass cylinders. This combination of rotation and flexure subjects more area and volume of a cylindrical test specimen to tensile stress than a standard static (nonrotating) flexural test. As anticipated, failure stresses were lower for the rotational flexural test. Expressions for effective area and volume are provided for rotating solid rods and tubes subjected to three‐point, four‐point, uniform, and uniformly distributed load bending configurations.

Effects of tool coating and tool wear on the surface quality and flexural strength of slotted CFRP

Machining of carbon fibre reinforced polymer (CFRP) is abrasive and causes significant tool wear. The effect of tool wear on static flexural strength is investigated, using edge trimming with uncoated carbide and chemical vapour deposition (CVD) diamond coated burr style tools. Edge rounding (ER) criteria along with flank wear are used to observe tool degradation with ER shown to preferentially wear allowing the tool to become cyclically sharper and duller, corresponding to fluctuating dynamometer readings, a novelty for CFRP machining. Areal surface metrics degraded for an uncoated tool due to changes in cutting mechanism, whilst for up to 16.2 m of linear traverse, the coated tool showed limited changes. Tool wear, caused by edge trimming 7.2 m of CFRP, using an uncoated carbide tool, provided a flexural strength reduction of up to 10.5 %, directly linking tool wear to reduced mechanical strength.

Damage and Fatigue Failure of Conventional and Bulk-Filled Resin Composites

Objectives: Resin-based composites are the most widely used dental restorative materials. Bulk-fill resin composites are of rising interest as they can be clinically applied in thicker increments compared to conventional composites. The purpose of the study was to evaluate the flexural fatigue strength of a conventional and bulk-filled resin composite placed incrementally or non-incrementally. Methods: Resin composite specimens were fabricated using either a conventional (Brilliant EverGlow?) or a bulk-fill (Fill-Up!TM) resin composite by either non-incremental filling (2 × 2 × 25 mm3) or in increments of (1 × 2 × 25 mm3). Specimens were stored in distilled water for 24 h or thermocycled for 5000 cycles. The static flexural strength (σ), flexural fatigue limit (FFL) after 105 cycles and post-fatigue flexural strength (PFσ) were measured. Data were analyzed using ANOVA, with a post-hoc Tukey’s test to compare mean FFL (p σ and PFσ compared to conventional composites regardless of incremental cure or thermocycling (p σ and FFL for conventional composites but not bulk-filled composites. There was no significant difference in PFσ compared to σ after 24 h storage, but a significant increase in PFσ after thermocycling (p < 0.05). Conclusions: The type of composite rather than incremental placement had a greater effect on flexural strength, suggesting that operator placement technique had less influence than material selection. Thermocycling in combination with cyclic loading caused a strengthening effect in the composites, likely due to the absorption and dissipation of stresses, thereby enhancing resistance to fracture.

Enhancement and underlying mechanisms of stainless steel wires to fatigue properties of concrete under flexure

In this study, the enhancement of stainless steel wires (SSWs) to the flexural fatigue performance of reactive powder concrete (RPC) including fatigue life and fatigue stress-strain hysteresis relationship as well as fatigue damage were investigated, and the underlying mechanisms were explored through microstructure observation and characteristic analyses of hydration products. The average flexural fatigue life of RPC is increased by 636.6%, 558.3% and 1010.7% at the maximum stress levels of 0.7, 0.8 and 0.9 when 1.5 vol% SSWs are incorporated. The method of moments and method of maximum likelihood are employed to calculate the scale and shape parameters for fatigue life subscribed to Weibull distribution. The calculated ratio of flexural fatigue endurance limit to static flexural strength for SSWs reinforced RPC reaches up to 0.64. The incorporation of SSWs decreases the flexural failure damage of RPC by 41.5% and converts the long and link-up micro cracks into emission cracks centered on SSWs. Benefited from the large specific surface area of SSWs, abound of silica fume with pozzolanic activity absorbs on the surface of SSWs and continues to hydrate, reducing the surrounding water-binder ratio to form a microstructure enhancement zone with SSWs as the core and improve the homogeneity of RPC. This can be confirmed by the decrease of porosity, Ca(OH)2 crystal orientation index and molar ratio of CaO to SiO2 for calcium silicate hydrate gels. SSWs can also enhance the fatigue performance of RPC by transmitting hydration heat, inhibiting the initiation and propagation of micro cracks especially at the initial stage of fatigue load, bridging cracks and being pulled-off. The excellent flexural fatigue properties and homogeneous microstructures of SSWs reinforced RPC make it particularly suitable for large-span and ultra-thin elements in extreme service environments.

Enhancement Research on Piezoelectric Performance of Electrospun PVDF Fiber Membranes with Inorganic Reinforced Materials

The electrospun PVDF fiber membranes with the characteristics of light weight, strong signal and measurability, have been widely applied in the fields of environment, energy sensors and biomedical treatment. Due to the weakness of the piezoelectric and service properties, the conventional PVDF fiber membranes cannot meet the operating requirements. Based on the obtained optimal technological parameter of electrospun pure PVDF fiber membranes (P-PVDF) in the previous experiment (unpublished), three inorganic reinforced substances (AgNO3, FeCl3·6H2O, nanographene) were respectively used to dope and modify PVDF to prepare composite fiber membranes with the better piezoelectric performance. The morphology and crystal structure of the hybrid fiber membranes were observed and detected by scanning electron microscopy and X-ray diffraction, respectively. The results showed that the dopant could effectively promote the formation of β-phase, which can enhance the piezoelectric performance. The mechanical properties test and piezoelectric performance test exhibited that the static flexural strength, the elastic modulus, and the piezoelectric performance were improved with the addition of dopant. In addition, the influence on the addition of dopant and the doping modification mechanism were discussed. Finally, the conclusions showed that the minimum average diameter was obtained with the 0.3 wt% addition of AgNO3; the piezoelectric performance reached the strongest with the 0.8 wt% addition of FeCl3·6H2O; the mechanical properties were best with the 1.0 wt% addition of nanographene.

Studying the behavior of geopolymer concretes under repeated loadings

This article investigates utilization of polypropylene microfibers as reinforcement in geopolymer concrete to enhance the ductility characteristics since the geopolymer concrete is considered a brittle material. The polypropylene microfibers were added to geopolymer concrete at the fiber volume content of 0.5%, 1.0%, and 1.5%. In this article, a slump test and compressive strength were tested for geopolymer concretes to measure the effect of polypropylene microfibers on geopolymer concretes. Also, static flexural strength and dynamic loading were applied to find out the attitude of polypropylene fiber-reinforced geopolymer concrete and to measure both the deflection and number of load cycles until failure. While comparing the results with reference geopolymer concrete, all samples were tested at 28 days and, finally, a statistical test was carried out. The results concluded that the use of polypropylene microfibers improves the compressive strength and enhances the properties of polypropylene fiber-reinforced geopolymer concretes, increases the loading for the appearance of the first crack, and decreases the deflection of polypropylene fiber-reinforced geopolymer concretes compared with reference geopolymer concrete.

Flexural fatigue properties and failure propagation of 3D stitched composites under 3-point bending loading

This work investigated the static and fatigue properties of 3D stitched composite and 2D laminated composite subjected to three-point bending loads. Four stress levels were carried out to investigate fatigue characteristics of the composites. The failure propagation of the composites and their fracture morphology were captured in detail using the high-speed camera. The results demonstrated that the static flexural strength of 3D stitched composite was lower than 2D laminated composite but the modulus of 3D stitched composite was higher than that of the latter. Besides, the fatigue failure mechanism of 3D stitching composite was dependent on the stress levels. Though the fatigue life of the 3D stitching composite was not as good as 2D laminated composite, the failure of stitching thread proved to be able to judge the catastrophic damage of the 3D stitching composite, which is important for indicating the safe use of the composite structure.