Increasing Fiber Content Research Articles

Strength and Stiffness Evaluation of a Fiber-Reinforced Cement-Stabilized Fly Ash Stone Dust Aggregate Mixture

The utilization of waste fly ash in road construction is primarily confined to its use in embankment filling or as a stabilizer when combined with lime and cement. Its application in structural pavement layers, such as the base and subbase, faces a challenge due to the high volume of fine particles, which renders it brittle when stabilized. In this study, fly ash was blended with stone dust and aggregated to enhance its gradation. Subsequently, it was stabilized with cement to bolster its strength, rendering it suitable for pavement use. Additionally, polypropylene (PP) fibers were introduced to mitigate the brittleness of the mixture. An extensive experimental investigation was conducted to assess the strength and stiffness properties, including compressive strength, indirect tensile strength, flexural strength, cyclic indirect tensile modulus, and flexural modulus of fiber-reinforced cement-stabilized mixtures of fly ash, stone dust, and aggregate. The experimental results reveal that the addition of PP fibers up to 0.25 wt.% enhances compressive strength, but any further increase in fiber content leads to a reduction in strength. However, indirect tensile strength and flexural strength show improvement, with an increase in fiber percentage up to 0.5 wt.%. It was observed that cement content plays a dominant role in stabilizing these materials. Appropriate relationships have been established between strength and modulus parameters for stabilized mixtures. Based on the strength and stiffness study, a combination of 70% fly ash and 30% stone dust aggregate with 6% cement can be considered for the base layer. Regarding the behavior of indirect tensile strength and flexural strength, an optimum fiber percentage of 0.35% is recommended.

Influence of basalt fiber on pore structure, mechanical performance and damage evolution of cemented tailings backfill

To study the influence of the addition of basalt fibers on the mechanical properties, pore structure, and damage evolution characteristics of the cemented tailings backfill (CTB), the uniaxial compression tests, nuclear magnetic resonance tests and scanning electron microscopy analysis were conducted on the CTB with four different content and lengths of basalt fibers. Test results show the following. (1) An increase in the content of basalt fibers will lead to an increase in the proportion of micropores and secondary pores in the CTB, while a decrease in the proportion of macropores. The influence of basalt fiber length on pore structure is not as significant as the content. (2) With the increase of basalt fiber content and length, the peak stress and peak strain of the CTB increase, but the elastic modulus decreases. Basalt fiber can significantly improve the ductility and bearing time of the CTB, with a length of 12 mm and a content of 1.5 % having the best effect. The length of basalt fibers affects macroscopic mechanics more than content. (3) The CTB without fiber have fewer cracks and faster crack propagation speed, while the CTB with fiber have more cracks and slower crack propagation speed. Basalt fibers mainly play a bridging role between hydration products, delaying the failure process of the sample. (4) A damage constitutive model was constructed. The rationality and reliability of the model were verified, and the damage evolution law of CTB was analyzed. The content and length of basalt fibers have a positive impact on damage evolution.

Mechanical properties and microstructure of SWGA-BF improved rock muck discharged from slurry shield tunnels

The waste muck discharged during shield tunneling has become the main source of urban construction waste. The modification of discharged muck from shield tunnels into roadbed materials can significantly improve resource utilization efficiency, but freeze–thaw environments can pose safety hazards. In this study, solid waste gelling agents (SWGAs) (50 % cement, 36 % blast furnace slag, 6 % calcium aluminate, 5 % semihydrate gypsum, 2 % calcium oxide, and 1 % alum) and basalt fiber (BF) were used as reinforcing materials for the waste muck discharged from the construction of slurry shield tunnels in rock formations. By conducting freeze–thaw cycle tests, unconfined compression tests, scanning electron microscopy (SEM) analysis, and image analysis by the ImageJ software, the effect of the freeze–thaw environment on the mechanical properties and microstructure of the improved tunnel muck by SWGA-BF composite was studied. The results show that the damage to the unconfined compressive strength (UCS) of the SWGA-BF improved tunnel muck caused by freeze–thaw cycling can be divided into three stages: rapid damage stage, slow damage stage, and basically stable stage, corresponding to N = 0 ∼ 3, N = 3 ∼ 9 and N > 9, and the damage degree generated by freeze–thaw cycle in each stage is 33.9 %, 16.7 %, and 5.0 %, respectively. The first freeze–thaw cycle causes the greatest damage. The variation characteristics of the elastic modulus of improved tunnel muck were similar to those of UCS, and the value of elastic modulus is linearly related to the UCS. The optimal content of BF is 0.5 %. As the fiber content increases, the yield strain and failure strain increase in a wavy manner. SEM tests reveal that the freeze–thaw environment increases the pore area, the size, and the number of fissures of the improved tunnel muck. However, after 12 freeze–thaw cycles, the particle diameter and abundance decreased by 20.46 % and 4.89 %, indicating that the freeze–thaw cycle effect has a greater impact on particle diameter than particle abundance. The deterioration of the microstructure eventually decreased the macro tunnel muck strength. These results have important reference values for the reutilization of waste muck discharged from shield tunneling for roadbed backfill materials in seasonally frozen areas.

Mechanical, Chloride Permeation, and Freeze–Thaw Resistance of Recycled Micronized Powder Polypropylene-Fiber-Engineered Cementitious Composites

Research on engineered cementitious composites was carried out using recycled micronized powder from waste construction waste as a substitute for cement. Consequently, this paper focuses on the investigation of recycled micronized powder (RMP) as the subject of study. Using RMP-PP-ECCA0 as the control group, we explored the impact of polypropylene fiber content (0.5%, 1%, 1.5%, 2%) and the substitution rate of RMP (10%, 20%, 30%, 40%) on the mechanical properties, resistance to chloride ion penetration, and freeze–thaw durability of recycled micronized powder polypropylene-fiber-engineered cementitious composites (RMP-PP-ECCs). It was found that, with the increase in RMP substitution rate and fiber content, the mechanical, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites showed a trend of increasing and then decreasing when the RMP substitution rate was 10%, and the fiber content was 1.5%; the compressive, tensile, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites were most obviously improved. Compressive strength performance increased by 18.8%, tensile strength performance increased by 80.8%, maximum tensile strain increased by 314%, and electrical flux decreased by 56.3%. Meanwhile, when the recycled micronized powder substitution rate was 10%, the fiber content was 1%, with the most obvious improvement in flexural and freeze–thaw cycle resistance, compared with the control group 28 d flexural strength increased by 22%, after 150 freeze–thaw cycles, the mass-loss rate was reduced by 26%, and the relative dynamic elastic modulus was improved by 4%. In addition, the chemical composition of the regenerated microfractions and the defects in the matrix of the fracture surface of the tensile specimens, the distribution of polypropylene fibers, the surface morphology, and the failure mode were analyzed by X-ray diffraction and scanning electron microscopy.

Increasing fibre in white flour and bread: Implications for health and processing.

Dietary fibre is beneficial for human health, but dietary intakes are below recommended levels in most countries. Cereals are the major source of dietary fibre in Western diets, with bread providing about 20% of the daily intake in the United Kingdom. Despite the promotion of fibre-rich wholegrain products, white bread (which has a lower fibre content) remains dominant in many countries due to cultural preferences. Increasing the fibre content of white bread and other products made from white flour is therefore an attractive strategy for increasing fibre intake. This can be achieved by exploiting genetic variation in wheat without major effects on the processing quality or the consumer acceptability of products. Modelling data for food consumption in the United Kingdom shows that increasing the fibre content of white flour by 50% (from about 4% to 6% dry weight) and in wholegrain by 20% will increase total fibre intake by 1.04 g/day and 1.41 g/day in adult females and males, respectively. Furthermore, invitro studies indicate that the increased fibre content of white bread should reduce the rate of starch digestion and glucose release in the human gastrointestinal tract.

Development and performance evaluation of alkali-activated multiple solid waste-based building foam insulation materials

To reduce building environmental pollution and energy consumption has become the mainstream development trend of today’s society. The building foam insulation materials (SWFIM) was developed by using blast furnace slag (BSF), waste photovoltaic glass (WPG), rice husk ash (RHA), and plant ash (PA), and the corresponding preparation technologies were proposed. The dry density, thermal conductivity, compressive strength, volumetric water absorption and pore structure parameters of SWFIM were measured. The effects of the amount of hydrogen peroxide solution (HPS), foam stabilizer (FS) and polyethylene (PE) fiber on the basic properties of SWFIM were discussed. The microscopic morphology of SWFIM was characterized by SEM (Scanning electron microscope) technology, and the mechanism of three influencing factors were revealed. The relationship between the basic properties of SWFIM was discussed and the corresponding prediction models were established. The test results showed that the effects of HPS and FS on the basic properties of SWFIM were complementary. When the amount of HPS and FS was 10 % and 1 %, respectively, SWFIM have achieved encouraging performance. PE fiber had different degrees of negative effects on the thermal properties of SWFIM, and the negative effects gradually increased with the increase of PE fiber content. The improvement effect of PE fiber on the compressive strength of SWFIM changes from positive influence to negative influence with the fiber content. When the fiber content increased to 0.6 %, the improvement effect was most obvious, increased by about 12.20 %. Statistics showed that the thermal conductivity and compressive strength of SWFIM were 0.0497 ∼ 0.0581 W/(m·K) and 0.33 ∼ 0.52 MPa, respectively. This showed that SWFIM was expected to become a potentially competitive building insulation material.

Evaluation of compression self-healing performance of a smart cementitious composite SMA-ECC

A two-stage compressive test was adopted to study the self-healing performance of a smart cementitious composite SMA-ECC under compression. The ultrasonic pulse and sorptivity tests were used to track self-healing ability and resistance to internal damage, respectively. A total of 32 groups of specimens, including 28 groups of SMA-ECC specimens and 4 groups of ordinary ECC specimens, were tested with various fiber contents and preloading levels. The strength recovery rate, relative dynamic elastic modulus recovery rate before and after self-healing, and cumulative water absorption were measured during the tests. It was found that the strength recovery rate of the SMA-ECC increased by 29.2% to 37.2% compared to the ordinary ECC. The elastic modulus recovery rate after self-healing of the SMA-ECC is approximately 3 to 10 times that of the ordinary ECC, and SMA-ECC with a 0.9% fiber content exhibits the best healing effect, with a remarkable 194% increase in elastic modulus recovery rate compared to ECC. As for internal damage, an increase in fiber content corresponds to a decrease in relative sorptivity coefficient (η) in most cases. Notably, for SMA-ECC specimens featuring a 0.9% fiber content, η reaches its nadir, hovering around 0.7. The situation takes an unexpected turn when fiber content hits 1%, as the relative sorptivity coefficient experiences a 14.9% increment compared to the SMA-ECC with 0.9% fiber content. Based on the test results, it is concluded that the SMA-ECC has excellent compressive recovery performance and the ability to resist internal damage. The optimal SMA fiber content for the self-healing performance of the SMA-ECC is determined to be 0.7% to 0.9%.

Environmental Properties of Coconut Fiber/Reinforced Thermoplastic Starch/Beeswax Hybrid Composites

The creation of degradable biocomposites is anticipated to alleviate the challenges of worldwide environmental contamination and resource exhaustion. The study investigates the effect of coconut fiber on the environmental properties and water affinity behavior of thermoplastic starch/beeswax composite. The biocomposites were fabricated by incorporating the coconut husk fiber range from 10 to 50 wt%. The thermoplastic starch contains cassava starch, glycerol, and beeswax. The modification of the mixture became efficient when the mixing was determined to be stronger when used as a high-pace blender to aid the mixing process. The mixture then underwent a hot compression molding method to form the mixture into the desired sample form. We can conclude from the results that samples with high fiber content absorb less water than those with no fiber content. For moisture absorption, when the fiber content increases, the ability of the fiber to moisture absorption is decreased. The thickness swelling results show that the sample shows less swelling as the fiber percentage increases. For the soil burial test, incorporating 50 wt% coconut fiber decreases the weight reduction for 4 weeks. For the water solubility test, the solubility of 50 wt% is the best. Based on the findings, integrating coconut fiber into the modified thermoplastic cassava starch increases the composite properties relative to the non-reinforcement matrix material starch.

Structural Performance of Ferrocement Panels under Low- and High-Velocity Impact Load.

The primary objective of this experimental study is to examine the response and energy absorption capacity of ferrocement panels exposed to low- and high-velocity impact loads. The panels are reinforced with two different types of mesh layers, namely, welded wire grid (WWG) and expanded wire grid (EWG), with varying percentages of steel fibers (SF). The ferrocement panel system is made up of cement mortar reinforced with 0-2% SF with an increment of 1% and wire grid layers arranged in three different layers 1, 2, and 3. A consistent water-cement ratio (w/c) of 0.4 is maintained during mortar preparation, and all panels are subjected to a 28-day curing process in water. The study utilized square-shaped ferrocement panels measuring 290 mm × 290 mm × 50 mm. The panels are exposed to repeated impact blows from a 2.5 kg falling mass dropped from a height of 0.80 m. The count of blows necessary to commence the first crack formation and the cause of ultimate failure are recorded for each panel. The study reports that an increase in SF content and the number of wire grid layers increased the number of blows needed for both the first crack and the ultimate failure. In the high-velocity impact test, 7.62 mm bullets are fired at the panels from a distance of 10 m with a striking velocity of 715 m/s. The study observed and analyzed the extent of spalling, scabbing, and perforation. The results showed that an increase in fiber content and the number of wire grid layers led to a decrease in the area of scabbing and spalling compared with the control specimens. It was also possible to see the mode of failure and crack pattern for impacts with low and high velocities.

Research on Fracture Behavior of Fiber-Asphalt Mixtures Using Digital Image Correlation Technology.

Many researchers use fiber to improve the cracking resistance of asphalt mixtures, but research concerning the effects of fiber on fracture behavior is limited. The fracture behavior of asphalt mixtures with various fiber types (basalt fiber, glass fiber, and polyester fiber) and contents (0.1%, 0.2%, 0.3%, 0.4%, and 0.5%) has been studied using the indirect tensile asphalt cracking test (IDEAL-CT) in conjunction with digital image correlation (DIC) technology. The evaluation indexes used in the test included crack initiation energy (Gif), crack energy (Gf), splitting tensile strength (RT), cracking tolerance index (CTindex), and the real-time tensile strain (Exx) obtained using digital image correlation technology. The results showed that despite the fiber type, the increase of fiber content resulted in first, an increase, and then, a decrease of the cracking resistance of asphalt mixtures, indicating the presence of optimum fiber content-specifically, 0.4%, 0.3%, and 0.3% for basalt fiber, glass fiber, and polyester fiber, respectively. The development of real-time tensile strain, obtained based on digital image correlation technology, could be divided into two stages: slow-growth stage and rapid-expansion stage. In addition, asphalt mixture with basalt fiber presented the best cracking resistance at both the slow-growth and rapid-expansion stages. This research is helpful in understanding the effects of fiber type and content on the fracture behavior of asphalt mixtures and has certain reference significance for the application of fiber in asphalt mixtures.

Effect of Glass Fiber-Reinforced Plastic Waste on the Mechanical Properties of Concrete and Evaluation of Its Feasibility for Reuse in Concrete Applications.

The disposal of glass fiber-reinforced plastic (GFRP) waste has become an urgent issue in both the engineering and environmental fields. In this study, the feasibility of reusing mechanically recycled GFRP in concrete was evaluated. Secondary screening of the recycled material was conducted to obtain different types of products, and the recycled GFRP (rGFRP) was characterized. Subsequently, the effect of rGFRP on concrete performance was evaluated using different dosages (0%, 1%, 3%, 5%) of rGFRP powder and rGFRP cluster (with different sizes and fiber contents) to replace fine aggregate in concrete preparation. The experimental results indicated that the addition of rGFRP powder has no significant impact on the mechanical properties of concrete, while the addition of a small amount of rGFRP cluster slightly improves the compressive strength and splitting tensile strength of concrete. Additionally, the short fibers in rGFRP improve the failure mode of concrete, and increased fiber content and longer fiber length demonstrate a more pronounced reinforcing effect. The challenges and potential directions for future research in the realm of reusing rGFRP in concrete are discussed at the end. A systematic process for reusing GFRP waste in concrete is proposed to address the primary challenges and provide guidance for its practical engineering application.

Early age dynamic mechanical properties of basalt fiber reinforced early strength concrete

AbstractThe dynamic compression test was carried out on basalt fiber reinforced early strength concrete (BFRESC) with ages of 4–24 h by the split Hopkinson pressure bar (SHPB) test system. The effects of curing age and basalt fiber content on dynamic mechanical properties of ESC was analyzed. The result shows that the dynamic compressive strength and specific energy absorption of BFRESC at early ages increase continuously with the increase of fiber content. The dynamic compressive strength of concrete at the early ages increases exponentially with the strain rate. With the increase of curing age, the strain rate sensitivity of dynamic compressive strength of concrete increases gradually, and the strain rate sensitivity of dynamic compressive strength of BFRESC with fiber content of 0.1% is the strongest. The specific energy absorption of concrete at early ages increases linearly with the strain rate. With the increase of curing age, the strain rate sensitivity of specific energy absorption of concrete increases gradually, and basalt fiber can enhance the strain rate sensitivity of specific energy absorption of concrete. Based on the comparison with the formula for dynamic increase factor (DIF) calculation provided by Comite Euro‐International du Beton (CEB), etc., a model of DIF based on the increase of curing age is proposed.

Preparation of carbon fiber conductive concrete and study on its mechanical and heating properties

Carbon fiber conductive concrete demonstrates great potential for effectively removing ice and snow from road surfaces. This study investigates the electrical conductivity and electromagnetic heating effects of carbon fiber conductive concrete, considering different carbon fiber dosages and temperatures. Experimental and numerical simulation methods were employed to assess the material's performance. The results show that as the carbon fiber content increases to 0.38 % and 1.5 %, the compressive strength decreases by 19 % and 55 %, respectively, which is related to the introduction of more bubbles and the agglomeration of carbon fiber when the carbon fiber is added, making it easier to produce stress concentration when the concrete is compressed. However, when the content of carbon fiber is small, the tensile properties of carbon fiber itself can improve the overall splitting tensile strength of concrete. With the increase of carbon fiber content, carbon fiber gradually forms a conductive network in the concrete, and the overall resistivity of the concrete decreases, but there is a certain threshold. Overall, 0.75 % fiber is the best solution. In addition, the heating process is accurately simulated by numerical simulation method. The simulation results are in good agreement with the experimental results, showing that the heating rate decreases with the increase of energizing time until reaching the heat equilibrium state. And the precise temperature distribution and change process that can be obtained through simulation provides valuable insights for engineering design.

Exploring the potential of sprouted soybean and sesame hull to increase nutritional value of ice cream

The study aimed to produce nutritionally enhanced ice cream by adding sprouted soybean (SSB) and sesame hulls (SH) at different concentrations to partially replace skimmed milk powder (SMP). The physicochemical, total phenolic content (TPC), antioxidant activity (AOA), and sensory acceptability of ice cream fortified with SSB or SH were evaluated. The ice cream containing 15% SSB was found to have the best sensory characteristics and was most preferred by the taste panel. The addition of 15% SSB increased the protein and fiber content and improved melting resistance, while the addition of 15% SH resulted in a greater increase in dietary fiber but lower protein content and melting resistance. The highest overrun on the cost was obtained in the sample fortified with 25% SSB compared to the lowest in the sample fortified with 25% SH, but panelists generally did not like these samples in terms of taste-flavor. The study concluded that the addition of SSB and SH to replace SMP in ice cream can create a nutritious and low-cost product with similar physicochemical properties and acceptance to the control.

Study on the Performance and Mechanism of Glass Fiber-Reinforced MgO-SiO2-H2O Cement.

The magnesium silicate hydrate system (MgO-SiO2-H2O) possesses issues such as susceptibility to cracking, brittleness, and poor volumetric stability, which hinder its development and practical use in engineering applications. This study aimed to enhance the properties of the MgO-SiO2-H2O system by incorporating glass fiber as a reinforcing material. The mechanical properties, shrinkage properties, and properties during accelerated aging were tested at different content levels of glass fiber. Additionally, the reaction mechanism and microscopic morphology were characterized using microscopic testing methods. The results revealed that the addition of glass fiber improved the mechanical properties of the MgO-SiO2-H2O system; meanwhile, with an increase in fiber content, the mechanical properties showed an initial increase followed by a decreasing trend. With a glass fiber content of 0.6%, the system exhibited a flexural strength of 7.9 MPa at 28 d, a compressive strength of 42.5 MPa at 28 d, and a 27.2% increase in splitting tensile strength compared to the control group. At a fiber content of 0.9%, the flexural toughness steadily increased, reaching a maximum value of 2.238 N·m, which is 5.41 times greater than that of the control group. Moreover, the incorporation of glass fiber effectively inhibited the shrinkage of the MgO-SiO2-H2O system. Accelerated aging experiments confirmed that the glass fiber in the MgO-SiO2-H2O system did not undergo significant deterioration or corrosion, thereby maintaining long-term stability. These findings have important theoretical and practical significance for the application and development of the MgO-SiO2-H2O system.

Significance of fiber characteristics on the mechanical properties of steel fiber-reinforced high-strength concrete at different water-cement ratios

The incorporation of fiber reinforcement into concrete is not a new approach to improving its ductility. In the past, research has generally focused on specific parameters, such as fiber type, dosage, slenderness, and the inherent strength of concrete. This study addresses the significant gap highlighted by ACI 544.1R by providing a deeper understanding of steel fiber-reinforced concrete (SFRC). The significance of the study is highlighted by the fact that it fills a crucial gap in research, especially considering the inaccuracy of current models related to flexural strength. The study examines in detail the influence of fiber dosage and length on the mechanical properties of SFRC using hooked-end fibers that range in length from 40 to 60 mm and diameters between 0.62 and 0.75 mm, as well as particular water-cement ratios (0.25, 0.35, and 0.45). The study also thoroughly evaluates the precision of widely accepted equations for predicting SFRC's compressive and flexural strengths. Results show that 0.5 to 1.5 % fibers increase concrete's compressive strength, inherent tensile strength, and peak flexural load capacity by 7–27 %, 11–47 %, and 3–124 %, respectively. However, it should be noted that despite the benefits of extending fiber lengths and increasing fiber content, the opposite has little effect on the flexural strength of SFRC. An original equation, which surpasses the existing models, is presented in this study to calculate the modulus of rupture in SFRC. Compared to independent datasets, this model proves remarkably accurate, boasting a predicted-to-tested ratio of 1.01, emphasizing its potential to advance SFRC research.

Study on mechanical and thermal properties of alkali-excited fly ash aerogel foam concrete

With increasing focus on low-carbon energy conservation and environmental protection, there is a need to consider all aspects of life in future developments. To meet the concept and requirements of energy conservation and environmental protection in the building industry, we have developed alkali-excited aerogel-foamed concrete that exhibits excellent thermal insulation performance and mechanical strength. The variables involved in its production include fly ash, foam, aerogels, and polypropylene fibres. In this study, the microstructure and mechanical and thermal properties of alkali-excited fly ash aerogel foam concrete was analysed. The results indicated that fly ash can replace a portion of the cement, resulting in a reduction in the thermal conductivity of the concrete. The addition of aerogels and foams to the concrete can significantly decrease its thermal conductivity. Specifically, when the aerogel content reaches 12 % and the foam content reaches 75 %, the thermal conductivity of the concrete decreases from 0.498 W/m·K to 0.183 W/m·K and 0.19 W/m·K, respectively. However, this decrease in thermal conductivity comes at a cost of approximately 50 % reduction in the flexural and compressive strengths of the concrete. The findings reveal that the aerogel has excellent thermal insulation performance similar to that of the foam, but it has little influence on the mechanical properties of the concrete. Additionally, an increase in the polypropylene fibre content significantly improves the mechanical properties of alkali-excited fly ash aerogel concrete, but the thermal properties of the concrete remain mostly unaffected.

Statistics of acoustic emission waveforms in characterizing the fracture process zone in fibre-reinforced cementitious materials under mode I fracture

This article reports on the characteristics of fracture process zone in steel fibre-reinforced concrete (SFRC) under the mode I fracture process using acoustic emission (AE) testing. The generated AE waveforms during mode I fracture process in SFRC were recorded in the laboratory. Using a statistical analysis of AE waveforms, it was observed that as the loading increases, a damage zone consisting of numerous microcracks develops ahead of the predefined notch tip. The location of the generated AE events related to the numerous microcracks were classified into three zones namely (i) major damage, (ii) moderate damage and (iii) low damage. The areas of these regions were evaluated from the distribution of the AE events around the pre-notch. The number of AE events reduced with the increase in the steel fibre content under the same experimental conditions. The major damage zone was located ahead of the notch tip very closely and it comprised of AE events with (i) high peak amplitude, (ii) low information entropy and (iii) longer AE waveform duration.

Construction of Human Periodontal Ligament Constitutive Model Based on Collagen Fiber Content.

Periodontal ligament (PDL) is mainly composed of collagen fiber bundles, and the content of collagen fiber is an important factor affecting the mechanical properties of PDL. Based on this, the purpose of this study is to explore the effect of the PDL collagen fiber content on its viscoelastic mechanical behavior. Transverse and longitudinal samples of different regions of PDL were obtained from the human maxilla. The fiber content at different regions of human PDL was quantitatively measured using image processing software, and a new viscoelastic constitutive model was constructed based on the fiber content. The nano-indentation experiment was carried out with a loading rate of 0.5 mN·s-1, a peak load of 3 mN, and a holding time of 200 s, and the model parameters were obtained through the experiment data. The results showed that with the increase of fiber content, the deformation resistance of PDL also increased, and compared with the neck and middle region, the compressive strain in the apical region of PDL was the largest. The range of reduced elastic modulus of human PDL was calculated to be 0.39~5.08 MPa. The results of the experimental data and the viscoelastic constitutive model fit well, indicating that the model can well describe the viscoelastic behavior of human PDL.

Bamboo fiber‐reinforced epoxy composites fabricated by vacuum‐assisted resin transfer molding (VARTM): Effect of molding sequence and fiber content

AbstractFabricating bamboo fiber‐reinforced epoxy composites (BFREs) using the vacuum‐assisted resin transfer molding (VARTM) process has many advantages, such as low cost, high product quality, controllability, and broad applicability. However, the immature fabrication process seriously affects product performance and hinders the full exploitation of the advantages of the VARTM process. The effects on the physical‐mechanical and thermal properties of BFREs by molding sequence and fiber content were investigated in this study. The molding sequence of fiber compression followed by resin injection was beneficial to ensure hermeticity, thus reducing the voids in the BFREs. The mechanical properties of BFREs gradually increased with increasing fiber content. With 50 wt% fiber content, the bending strength and modulus, shear strength, and impact toughness of BFREs reached 71.27 MPa, 6.78 GPa, 11.68 MPa, and 5.45 kJ/m2, respectively. Although the thermal stability of the BFREs was slightly lower than that of pure epoxy, the bamboo fibers' high rigidity evidentially increased the epoxy's dynamic mechanical properties. The life cycle assessment indicated that the BFREs effectively reduced the environmental impacts and production energy consumption compared to the glass fiber correspondent. The VARTM‐fabricated BFREs have great potential for construction, transportation, household items, packaging, sports equipment, and leisure goods applications.Highlights Fiber compression followed by resin injection could ensure great hermeticity. Micro‐CT accurately measured the void characteristics of the composites. Voids had detrimental effects on the properties of the composites. Dense bamboo fiber preforms enhanced the mechanical properties of epoxy. Bamboo fibers reinforcing epoxy reduced the impact on the environment.