Strength Retention Rate Research Articles

The excellent protection effects of silicon/ytterbium silicate bilayer environmental barrier coatings on SiCf/SiC composites

AbstractThe protection effects of an environmental barrier coating (EBC) consisting of silicon bond coat and mixed ytterbium monosilicate and ytterbium disilicate composite topcoat are directly evaluated by measuring the strength retention rate of SiCf/SiC composites completely wrapped up by the previous EBCs after soaking in a mixed oxygen and water vapor environment at 1300°C for up to 200 h. The results show that the mixed topcoat exhibits not only extremely excellent phase stability but also fantastic protection effects toward composites. After 200 h of corrosion, the fully protected composites are unveiled to present not only dramatically reduced weight gain ratios, less than .6%, compared to ∼10% for those unprotected ones, but also extremely higher strength retention rates, more than 90%, compared to only 10%–15% for those unprotected ones. Further, the fully protected composites show a quasi‐ductile load versus displacement curve, suggesting the retention of the oxidation‐prone pyrolytic carbon interphase of current composites.

Influence of moisture absorption on mechanical properties and damage mechanisms of three-dimensional six-directional braided composites under hydrostatic pressure

Fibre-reinforced composites have shown a growing interest in pressure-resistant materials for deep-sea use due to their excellent properties. This paper presents the influence of the moisture absorption on the mechanical properties and damage mechanisms of three-dimensional six-directional (3D6D) braided composites under hydrostatic pressure. The bisphenol A epoxy resin, bisphenol F epoxy resin, and hydrogenated bisphenol A epoxy resin, are chosen. SEM and X-ray Micro-CT are employed to investigate the moisture absorption, tensile and compressive damage before and after subjecting to the hydrostatic pressure. Results show that the bisphenol F carbon/epoxy composite has the lowest porosity at 0.082% among the three composite materials. The average moisture absorption was the lowest at 0.3755%. Furthermore, moisture is mainly transported along micro cracks in the matrix and the fiber-matrix interface under hydrostatic pressure. After the composites absorb moisture, the average tensile strength retention rates of bisphenol A carbon/epoxy composite, bisphenol F carbon/epoxy composite, and hydrogenated bisphenol A carbon/epoxy composites drop to 88.282%, 76.34%, and 66.43%, respectively. Moreover, their average compressive strength retention rates drop to 53.15%, 74.26%, and 83.45%, respectively. The tensile and compressive strengths of the 3D6D braided composites decreased significantly after moisture absorption, mainly due to fiber-matrix debonding and matrix cracking.

Firing properties and erosion resistance of hibonite-cordierite sagger

The sagger, an important storage and transportation component in the firing process of Li-ion battery cathode materials, is mainly fabricated using Al2O3–SiO2–MgO (cordierite-mullite/spinel) composites. Unfortunately, these materials are prone to react with the cathode resulting in secondary phases such as eucryptite (β-LiAlSiO4), which cause volume expansion and consequently damage the sagger. Moreover, this reaction leads to the delithiation of the cathode. In this study, hibonite with excellent alkali resistance was used as the main raw material, and cordierite, α-Al2O3 and zircon were introduced to investigate the firing performance and erosion resistance mechanism of hibonite-cordierite (CA6-M2A2S5) sagger. The results showed that the sagger exhibited the best overall performance after firing at 1380 °C for 3 h with a bulk density of 2.43 g/cm3, and cold and hot moduli of rupture of 21.07 MPa and 11.20 MPa, respectively. The samples exhibited a strength retention rate of 22.5% after five thermal cycles at 1100 °C for 30 min. At this firing temperature, a dense protective layer of anorthite was formed along the edges of the hibonite particles. This layer inhibited the reaction between the cathode and sagger, improving the sagger's resistance to erosion.

Blast and tensile properties of tantalum/niobium lined SiC/SiC composite tubes for nuclear cladding

The mechanical performances such as tensile strength and blast property of metal lined SiC/SiC composite cladding tubes were investigated. Nb or Ta was selected as liner material, and the SiC/SiC composite layer was fabricated by winding and different precursor impregnation and pyrolysis (PIP) processes. The tensile strengths of different tube samples were measured at room temperature (RT) and 1200 °C, respectively. The blast property was investigated through the maximum water pressure of tubes. And the fracture microstructures were observed by SEM. The highest tensile strength at RT was 150.7 MPa. The blast strength was enhanced with the PIP process increasing from 1 to 4 cycles and the tube of 4 PIP cycles had the highest water pressure of 34.7 MPa. Compared with the metal tubes, the multi-layer structure improved tensile and blast properties significantly. The different processes such as PIP cycles and pyrolytic carbon (PyC) coating were important factors to enhance the mechanical performances of SiC/SiC-based tubes. However, the retention rate of tensile strength was only 18.5% at 1200 °C.

Research and Development of Organic/Inorganic Mixtures Compound Coated Antioxidants

For plastic thermal oxidative aging, it is inevitable that the material properties will decline and eventually lead to product damage. It is very important to improve the performance retention rate of materials under aging conditions and ultimately delay the damage to prolong the service life of products. In this study, nano-zinc oxide was selected as the compound auxiliary antioxidant of the main antioxidant 1010. Nano-zinc oxide is very obvious to improve the comprehensive performance of plastics. The retention rate of the tensile strength and elongation at break of the plastic in the test is significantly improved after hot air aging due to the small size effect of nano-zinc oxide increases the cross-linked network density, which is related to the realization of molecular-level bonding of polymer materials. This study not only innovated in the selection of materials which selected nano-zinc oxide as an auxiliary antioxidant, but also realized the coating structure of the main/auxiliary antioxidant by changing the process conditions, so as to finally realize the ideal mixing and distribution of the main/auxiliary antioxidant, to improve the mechanical properties of general-purpose plastics after introduction, and ultimately optimize the antioxidant properties.

Thermal degradation behavior of flame-resistant fabrics exposed to fires: effect of air gap type and thickness

The thermal degradation of flame-resistant fabrics reduces the protective ability of clothing and affects firefighters’ safety. Making clear the influence factors of fabric thermal degradation is important for predicting and prolonging the service life of fire-protection clothing. Experiments were conducted for open and sealed air gaps with different thicknesses under flame exposure. The degradation the of outer shell fabric was evaluated by observing the variation in fabric morphology, mass loss and tensile strength of specimens after heat exposure. The influence mechanism of the type and thickness of the air gap on thermal degradation was analyzed by the surface temperature curve and thermal stability of the fabric, as well as the microstructure of the fiber. The results indicated that the type and thickness of the air gap have a significant effect on thermal degradation, and a more serious negative effect was observed under the condition of an open air gap. After being exposed to heat fluxes of 30 and 50 kW/m2 for 40 s, the mass loss rates were 1.8% and 3.3% higher than those of the sealed air gap, and the tensile strength retention rates were 9.1% and 10.1% lower on average, respectively. Air gap type and thickness affected the heat storage and heat transfer efficiency in the fabric system by changing the heat transfer mode. The decomposition and fracture of the fabric were affected, which made the flame-resistant fabrics show different degrees of thermal degradation.

Performance Analysis of Soluble Bridge Plug Materials for Fracturing in Unconventional Oilfields

With the continuous in-depth development of oil and gas resources, unconventional oil and gas resources show great potential. In recent years, 70% of the proven oil and gas resources in China are unconventional oil and gas resources. Therefore, the development of unconventional oil and gas resources has a huge impact on the increase in the production capacity of the oil and gas resources in China. Staged fracturing of horizontal wells is the main technical measure to improve unconventional oil and gas production stimulation. In the fracturing process, the soluble bridge plug technology can not only effectively solve the problems of large investment in drilling and grinding of composite bridge plugs, high risks, self-locking of oil, casing deformation, etc., causing the bridge plug to be unable to be drilled and remove and affect subsequent production but also can successfully make up for the problems of subsequent production. The large-diameter bridge plug cannot achieve the full diameter of the wellbore and cannot carry out operations such as postproduction logging and refracturing, which can ensure the integrity of the wellbore to the greatest extent. In this paper, HNBR was used to modify MPU to prepare HNBR/MPU soluble rubber, and the effect of blending ratio on the vulcanization characteristics, mechanical properties, compatibility, thermal stability, and degradation behavior of composites was studied. The results showed that with the increase in the amount of HNBR, the degree of cross-linking of the composite material decreased gradually, and the mechanical properties decreased slightly. With the increase in the amount of HNBR, the thermal stability of the material decreases. The use of HNBR greatly reduced the degradation rate of MPU. When the amount of HNBR was changed from 20 phr to 40 phr, the tensile strength retention rate of the composite after soaking increased from 14.73% to 39.72%.

Properties of MgO–SiO2–K2HPO4 cement modified with ground blast furnace slag

In this article, a new chemically-bonded ceramic composite, called magnesium silicon potassium phosphate cement (MSPPC), without retarders, is prepared from dead-burnt magnesium oxide, silica fume and dipotassium hydrogen phosphate (K2HPO4 or DHP). MSPPC has excellent workability and mechanical properties, but the water resistance still needs to be improved (its strength retention rate is only 78.41% after 90 days of water immersion). Notably, in contrast to the acidic or near-neutral pH internal environment of traditional magnesium potassium phosphate cement (MKPC), the MSPPC system has a unique high-alkaline internal environment, which appears to have the natural alkali-activated conditions. In order to improve the water resistance, the effect of slag on MSPPC is studied. The results show that with the increase of slag content, the fluidity decreases, the setting time increases and the pH value of the hydration process rises. After 90 days of air curing, the specimens containing 10 wt % of slag can reach a maximum flexural and compressive strength of approximately 27.2 MPa and 124.8 MPa, respectively. The best water resistance is achieved when the slag content is 20 wt %, with a strength retention rate of 90.42% after 90 days of water immersion. The hydration mechanism of slag in MSPPC system is also different from that in traditional MKPC system. The hydraulic nature of slag can be effectively activated by KOH, K2SiO3 and MgSiO3 (the hydration products of MSPPC). The BSE-EDS, 29Si MAS NMR and SEM-EDS tests show that Ca, Al and Si elements in the slag are released into solution and combined with Si elements in the MSPPC system to produce C-(A)-S-H gels. Such gels wrap around the surface of the soluble substance and, together with the physical filling effect of the slag, contribute to the mechanical strength and water resistance of MSPPC.

Improvement in water resistance of magnesium oxychloride cement via incorporation of dredged sediment

Dredged sediment (DS) derived from dredging operations poses a potential threat to the ecological environment. The proper disposal and utilization of DS remains a challenge. In this study, magnesium oxychloride cement (MOC) was adopted as a sustainable carrier for effective recycling of DS. MOC pastes incorporated with DS or calcined dredged sediment (CDS) were subjected to multiscale characterization techniques to investigate the feasibility of combining MOC with DS. DS/CDS were found to enhance the water resistance of the MOC pastes despite the negative influence of dilution on their mechanical properties. Strength retention tests revealed that the compressive strength retention rate of MOC pastes blended with 10%–40% DS positively correlated with the DS content, and the modification induced by DS was superior to that by CDS. Multiple microscopic approaches were adopted to mechanistically elucidate the modification of MOC by DS/CDS. The results revealed that the addition of DS increased the porosity of the modified MOC pastes, thereby providing more channels for water intrusion. Interestingly, the improvement in the water resistance of the MOC paste was sustained with increasing DS content. Insoluble gel-like phases were observed throughout the MOC substrate and acicular phase 5 crystals, which impeded the intrusion of water and consequently improved the water resistance of the MOC pastes. Thermogravimetric and energy-spectrum analyses confirmed that the insoluble phases were composed of an amorphous Mg–Al–Si–Cl–H gel. The development of this MOC paste demonstrates a promising strategy for improving the water resistance of MOC products and alleviating the burden of DS on the environment.

Oxidation inhibition behaviors of environmental barrier coatings with a Si-Yb2SiO5 mixture layer for SiCf/SiC composites at 1300 °C

Atmospheric plasma spraying (APS) process was employed to produce four-layer Si/Si-Yb2SiO5/Yb2SiO5/LaMgAl11O19 environmental barrier coatings (EBCs) for SiCf/SiC composites with SiC sealing layer. The bending strength of the specimens after isothermal oxidation was investigated. The specimens with EBCs especially thanks to the Si-Yb2SiO5 mixture layer showed a high bending strength retention rate with “psesudo-plastic” fracture. The Si-Yb2SiO5 mixture layer could remarkably enhance the oxidation resistance and also prolonged the life of the EBCs. Such obvious improvements in the Si-Yb2SiO5 mixture layer were attributed to that Yb2SiO5 reacted with TGO (SiO2) to in-situ form a dense Yb2Si2O7 layer, which was conducive to control the thickness of the TGO and prevent the prolongation of the cracks.

Microstructure, high-temperature mechanical and dielectric properties of novel Si3N4 f/SiNO wave-transparent composites

Continuous Si3N4 fiber reinforced SiNO matrix composites (Si3N4 f/SiNO composites) were innovatively prepared for long-time high-temperature resistant wave-transparent materials of hypersonic aircraft. The microstructure, high-temperature mechanical and dielectric properties of Si3N4 f/SiNO composites were investigated in detail. The as-fabricated Si3N4 f/SiNO composites have homogeneous SiNO matrix distribution for the special winding process, which is beneficial for the mechanical strength and wave-transparent properties. The average tensile strength and flexural strength at room temperature is 87.8 MPa and 171.2 MPa respectively, which suggests Si3N4 f/SiNO composites have excellent mechanical strength. The tensile strength value decreases to 54.6 MPa after heat-treated at 1000 ℃ for the surface reactions between the SiNO matrix and Si3N4 fibers. After heat-treated at 1550 ℃, the composites have the tensile strength value of 24.2 MPa for the high strength retention rate of Si3N4 fibers at this temperature. Si3N4 f/SiNO composites have excellent room temperature dielectric properties and excellent dielectric stability in different frequency bands (7–18 GHz). The dielectric constant values vary from 3.69 to 3.75 while the dielectric loss attains the order of 10−3. The dielectric constants and dielectric loss of Si3N4 f/SiNO composites are relatively stable from RT to 800 ℃. The as-fabricated Si3N4 f/SiNO composites that have excellent high temperature resistance and dielectric properties are the ideal high temperature wave-transparent composites.

Study on polyetheretherketone prepreg manufactured by aqueous system of powder impregnation

AbstractAiming to improve safety and stability in manufacturing poly‐ether‐ether‐ketone (PEEK) prepreg by powder impregnation, the aqueous system combined with surfactant and thickener was proposed in this paper. Based on surface tension method, the effects of surfactants and concentration on dispersion efficiency of PEEK powders were studied, and concentration of surfactants was determined. The effect of thickener concentration on suspension stability was analyzed, and ingredients of aqueous system were optimized by mechanical tests. The results show that, dispersion efficiency would reach maximum when surfactant concentration at critical micelle concentration, but not affected by the type of surfactant. Network association mechanism of thickener could improve stability of suspension, which holding time was increased from 40 min to 4 h. The good dispersion effect and long times stable system improved the coefficient variation of resin mass fraction, which was reduced from 7% to 4%. Compared with circulating system, the mechanical test results showed that the tensile strength kept unchanged, but interlayer properties were associated with carbon residue mass, the lower the residue carbon mass, the higher the interlayer strength retention rate, the optimized ingredient was Aerosol OT 75%E solution. Aqueous system has characteristics of safety, green, and low cost, which fits the demands of industrial production of prepreg.

Effects of seawater temperature and NaCl concentration on interlaminar shear behavior of CFRP laminates

The aim of this paper is to study the interlaminar shear behavior of CFRP in critical service conditions. The specimens were immersed in the prepared artificial seawater for 7 months to investigate the ageing time, ambient temperature and salt concentration effects. Analytical balance was used to weight the samples for analyzing the dynamic moisture absorption behavior. Short beam shear tests were carried out to evaluate the interlaminar shear properties. Scanning electron microscopy (SEM) was used to observe the ageing damage and failure morphology. The results show that moisture absorption behavior of composites follows Fickian diffusion law. Moisture absorption rate and the maximum absorption content are mainly affected by ambient temperature but not by NaCl concentration. Compared with ageing time and NaCl concentration, the shear stiffness and shear strength are more sensitive to aging environmental temperature. After exposed in 3.5%–70 °C seawater environment for 7 months, the retention rate of shear strength is only 68.8% and the failure displacement decreases by 20.5%. The shear strength increases first and then decreases with the increase of the maximum moisture absorption, which is mainly related to the release of curing shrinking stress and the damage of interface properties. The shear properties degradation after aging is mainly related to the damage of materials induced by environment (delamination, fiber/matrix interface debonding and matrix cracking).

Solvent-free rapid degradation of epoxy composites and recycling application of high performance carbon fibers through the synergic catalysis effect of molten salts and titanium dioxide

Along with the massive application of the carbon fiber reinforced polymer (CFRP), the quantity of CFRP wastes are rapidly increasing, becoming an urgent issue to be resolved. Here, an effective solvent-free treatment method was proposed to recycle carbon fiber/epoxy composite wastes and reclaim the carbon fibers with high performance. The resin matrix composed of tetra-functional epoxy/aromatic amine system which is widely used in aircraft components can be decomposed rapidly in KCl/ZnCl2 molten salts due to triggered C-N bond cleavage under the catalytic effect of cations at 350 °C in 90 min, and TiO2 can facilitate the removal of pyrolysis carbon within 10 min subsequently. In addition, the reclaimed fibers had similar chemical structure and graphitization degree to the commercial fibers, and also the tensile strength retention rate was up to 97.8%. The reclaimed carbon fibers showed a comparable reinforcing effect for the polypropylene in comparison to the commercial fibers, without visible influence on processability, thermal stability and crystallization behavior of matrix, showing valuable application potential in the field of composite materials. Therefore, this study devised a novel high-efficiency technique applicable for industry to reclaim high-performance carbon fibers from epoxy composite wastes under a mild condition, which showed a significant application value in term of the environmental protection and sustainable development.

Assessment of the mechanical properties and water stability of nano-Al2O3 modified high ductility magnesium potassium phosphate cement-based composites

The large-scale application of high ductility magnesium potassium phosphate cement-based composites (HDMPKC) is limited by the poor stability of magnesium potassium phosphate cement (MKPC) in water or a humid environment. Nano-Al2O3 (NA) was incorporated into the HDMPKC to improve its water stability. The effects of NA content on the workability, compressive strength, flexural behavior, and water stability of the HDMPKC were examined. The results showed that compared with the HDMPKC without NA, 2–6% NA had little effect on the workability; when the NA content was less than 8%, the compressive strength, cracking strength, flexural strength, ductility index, and toughness index were significantly improved. Meanwhile, the NA could improve the strength retention rate, ductility index retention rate, and toughness index retention rate of the HDMPKC that are more than 100%, slightly lower than 100%, and around 100%, respectively, indicating an improved water stability. The scanning electron microscopy results showed that for the matrix with NA, the surface was smooth, and the structural integrity was relatively good, with fewer cracks, which prevented water from entering the matrix and thus resulted in good water stability. Moreover, the NA could improve the bonding between the matrix and fibers, improving the mechanical properties of the HDMPKC.

Torrefaction pretreatment facilitated solvents-resistant and stable wood-plastic composites

Solvents-resistant and stable wood-plastic composites have been successfully obtained via combined torrefaction pretreatment, extrusion, and injection molding processes that applied torrefied sweet sorghum slag (SS) fibers as reinforcing fillers and high-density polyethylene (HDPE) as thermoplastic polymer matrices. Comparing with intact SS fibers, torrefaction pretreatment caused deacetylation and severe decomposition of hemicellulose (decomposed nearly 95% under 300 °C) in SS fibers, which was favorable for the formation of porous structures on the surface of SS fibers and the increase in their hydrophobicity. Thus the resultant composites exhibited enhanced mechanical properties (max tensile strength of ~24.84 MPa, flexural strength of ~32.63 MPa, and toughness of ~2.50 MJ/10−3), and promising solvents resistance (e.g., H2O, acid, alkali, salt, and ethanol) and stabilities (e.g., thermal, and dynamic mechanical stabilities). The mechanical strength retention rates of HDPE/torrefied SS (300 °C) composites maintained above 95% after socking in common solvents for 7 days. Moreover, torrefaction took advantages of short processing time, energy-saving, low-cost, and high mass yield when compared to the traditional carbonization, which paved an efficient and scalable biomass fibers pretreatment strategy to construct highly stable wood-plastic composites and extended their application areas like constructing materials and some extreme circumstances.

Preparation and characterization of corundum ceramics doped with Fe2O3 and TiO2 for high temperature thermal storage

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe2O3 and TiO2 were prepared via a pressureless sintering. A Fe2O3–TiO2 system with different Fe2O3/TiO2 ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe2O3 and TiO2 rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe2O3/TiO2 ratio led to a new phase of FeAlTiO5, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO5 and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe2O3/TiO2 ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.

The use of artemisia sphaerocephala Krasch. gum as an eco-friendly stabilizer to improve the mechanical properties of disintegrated carbonaceous mudstone

Carbonaceous mudstone is widely distributed in many areas. Its disintegrated material has attracted great interest as a low-cost embankment filler. However, the poor mechanical properties of the disintegrated carbonaceous mudstone (DCM) prevent its widespread application. In this paper, we report the use of artemisia sphaerocephala Krasch. gum (ASK gum) to improve the mechanical properties of DCM. A series of DCM/ASK gum mixtures containing 0 to 8% ASK gum have been prepared and examined by direct shear, unconfined compressive strength, dry-wet cycle, and permeability tests. When 4% ASK gum is incorporated, the unconfined compressive strength of the mixture cured at a duration of 14 days increases by 380%. After 8 dry-wet cycles, the strength of the DCM/ASK gum mixture is 6.4 MPa, which is 12.8 times higher than that of untreated DCM, and the strength retention rate is 61.5% compared to that of 45.5% for untreated DCM. When the normal pressure is 100 kPa, the shear strength increases by 50.0%. In addition, the permeability coefficient was reduced to only 15.9% at 96% compaction degree when only 1% ASK gum is introduced. Scanning electron microscope measurements disclose that the ASK gum can cross-link the DCM particles to form a compact and flat structure, which explains the improved mechanical properties. As both DCM and ASK are abundant, low-cost, and environmentally friendly, the mixture with substantially improved mechanical properties can be a very promising filling material for embankment application.

Relationship between Anti-Wrinkle Property of Cotton Fabrics and Crosslinking Properties of Glycosyl Polyaldehydes and Polyuronic Acids Finishing Agents: A Molecular Simulation Study

In this paper, monosaccharide (glucose and fructose), disaccharide (sucrose and trehalose), trisaccharide (raffinose) and tetrasaccharide (stachyose) were selected as the research objects and the glycosyl polyaldehydes and glycosyl polyuronic acid anti-wrinkle finishing agents were prepared via selective oxidation. The anti-wrinkle properties of their finished fabrics were analyzed, the molecular radius, the number of reactive groups, the number of reaction sites and the number of rotatable bonds of the finishing agent were calculated to evaluate its diffusion rate and crosslinking characteristics inside the cellulose. Through molecular simulation, the number of possible conformations of the anti-wrinkle finishing agent with the single cross-linked state was calculated, and the distance between different cross-linking points was measured, and the relationship between the effective cross-linking radius and the anti-wrinkle performance was studied. The results showed that trehalose polyaldehydes, raffinose polyaldehydes, trehalose polyuronic acid, and raffinose polyuronic acid finished fabrics had an excellent anti-wrinkle property, the strength retention rates of the fabrics were all above 68%, and the whiteness index was above 70. The smaller the molecular radius was, the easier the finishing agent was to diffuse into the cellulose. The most suitable crosslinking radius of glycosyl finishing agent was 3.5–6.0 Å.

EFFECT OF NATURAL AND ACCELERATED AGING ON THE PROPERTIES OF WOOD-PLASTIC COMPOSITES

The correspondence of natural and laboratory-accelerated aging of WPC has long beenahighly important problem discussed by many scholars. In this work, the changes in moisture content (MC), modulus of rupture (MOR), modulus of elasticity (MOE), screw holding force and creep recovery rates of two groups of wood-plastic composites (WPC) after natural and accelerated aging (high-low temperature cycles and freeze-thaw cycles) were studied to provide guidance for the use of WPC in outdoor applications. The results showed that, after the natural aging and freeze-thaw cycles treatments, MC increased significantly with both 167% of the untreated value of wood-HDPE composites with 30% wood fiber content and a thickness of 25 mm (W25), while 67% and 133% of the wood-HDPE composites with 30% wood fiber content and a thickness of 20 mm (W20), but is almost unchanged after the treatment with high-low temperature cycles. The mechanical strength, including MOR, MOE, screw holding force and creep recovery rate, decreased after natural and accelerated aging. The greatest decreases of MOR, MOE, screw holding force and creep recovery rate were 14%, 13%, 21%, and 7% for W25, while 5%, 8%, 8%, and 14% for W20 respectively. Environmental aging can reduce the strength of WPC, but the bending strength retention rate is more than 85%, showing that performance of WPC is relatively stable compared to wood materials, which is oneof thereasons for the widely use of WPC in outdoor applications.