Optimum Fiber Length Research Articles

Influence of reference path length on self‐heterodyne‐based Brillouin observation

AbstractFibre‐optic distributed Brillouin sensing that utilises correlation‐domain techniques often requires an optical delay fibre in the reference path to control the correlation peak order in the sensing fibre. Nonetheless, a suboptimal delay fibre length can result in decreased performance. In this work, as a first step towards clarifying the optimal delay fibre length for Brillouin correlation‐domain sensing, the authors evaluate the effect of changing the delay fibre length on the Brillouin gain spectra in a full‐length measurement scenario.

Mechanical, thermal, and morphological behavior of pineapple leaf fibre and polylactic acid green composites fabricated by varying fiber loading, fiber length, and injection parameters

AbstractIn this article, gray relational analysis (GRA) was carried out to study the influence of fiber length, fiber loading, and injection parameters on the mechanical, thermal, and morphological properties of the developed green composites. The green composite was developed by chemically modifying the pineapple leaf fiber (PLF). PLF was chemically treated with 1% Na2CO3 for a period of 6 h. The chemically modified PLF was chopped at a fiber length (L) of 2, 3, 4, 5, and 6 mm. The fiber loading (D) was also varied to 10, 20, and 30 wt% to study the effect of both fiber length and loading on the tensile and flexural properties of the PLF/PLA green composite developed through injection molding. GRA was employed to determine the optimal fiber length and fiber loading for achieving better tensile and flexural properties of PLF/PLA green composite. The injection parameters considered for producing the PLF/PLA green composite were (a) injection pressure (70, 90, and 110 bars), (b) injection speed (40, 50, and 60 mm/s), and (c) melting temperature (165, 175, and 185°C). The mechanical (tensile, flexural, compression, and shear) and thermal (TGA: thermogravimetric analysis and DTG: derivative thermogravimetric analysis) behavior of the developed PLF/PLA green composite was studied and analyzed. The morphology of the fractured specimens was also inspected using field‐emission scanning electron microscope (FESEM).

Effect of Palm Fiber Reinforcement on the Unconfined Compressive Performance of Cement-Treated Sand

This research studies the unconfined compressive characteristics of cement-treated sand reinforced with palm fiber. Type 1 Ordinary Portland cements with 3, 5, and 7% dry sand weight were mixed with sand and different amounts of water to produce cement-treated sand. Palm fiber contents of 0.5, 1, and 2% volume and fiber lengths of 10, 20, and 40 mm were utilized. Three performance parameters were considered to assess the performance of the cemented sand reinforced with palm fiber: peak strength, strain ratio, and toughness. The results showed that incorporating palm fiber elements could improve the peak strength and ductility and reduce brittleness by increasing the fiber content and length. All palm-fiber-reinforced samples showed a softening behavior and changed the behavior of cement-treated sand from brittle to semi-ductile or ductile. The compressive strength of reinforced cemented sand increased when the fiber length was 40 mm, and the compressive strength was reduced as the fiber content exceeded 1.0%. Palm fiber was the most efficient at increasing the toughness of the cemented specimen because of its rigidity and bridging ability. The optimum fiber content and length for the cement–treated sand were 1.0% and 40 mm, respectively.

Microstructure and mechanical performance of bamboo fiber reinforced mill-scale—Fly-ash based geopolymer mortars

Natural fiber reinforcement in cementitious matrices is being explored to provide an environment-friendly solution for lowering the overall carbon footprint of construction materials while giving the matrix much-needed tensile strength. Short bamboo fibers extracted from Bambusa blumeana or Kawayan tinik using 5% sodium hydroxide solution and treated with 10% aluminum sulfate solution are used to reinforce zero-cement geopolymer mortars. Bamboo fibers with varying lengths of 10 mm, 20 mm, and 30 mm are mixed with mill-scale – fly ash-based geopolymer in varying 0%, 0.5%, 1%, 1.5%, and 2% fiber loading per weight of specimen sample. Compressive strength and split tensile strength tests are administered to small cylinder samples, 50 mm in diameter by 100 mm in height, in accordance with ASTM C780. An optimum fiber length of 20 mm and fiber loading of 1.4% by weight is determined using Response Surface Methodology (RSM). The addition of bamboo fibers increased the unconfined compressive strength up to 292.41% compared to specimens without bamboo fibers. The split tensile strength also improved by up to a 355.82% increase compared to control samples. The corresponding high-strength and low-strength samples are also subjected to Fourier-transform Infrared Spectroscopy – Attenuated Total Reflectance (FTIR-ATR) to investigate and compare the stretching of bands between the raw materials and tested specimens. Scanning Electron Microscopy – Energy Dispersive X-Ray analysis (SEM-EDX) is used to show microscopic images and the elements present in the selected samples. The implications of the results on the material development of bamboo fiber-reinforced geopolymer mortar for construction are discussed.

Direct measurement of human skeletal muscle specific tension and fiber length

Skeletal muscle’s isometric contractile properties are one of the classic structure-function relationships in all of physiology allowing for extrapolation of single fiber mechanical properties to whole muscle properties based on the muscle’s optimal fiber length and physiological cross-sectional area (PCSA). However, this relationship has only been validated in small animals and then extrapolated to human muscles which are much larger in terms of length and PCSA. We leveraged a unique surgical technique in which an intact, living, human gracilis muscle is transferred from the thigh to the arm, restoring elbow flexion after brachial plexus injury. During this surgery we directly measured subject specific gracilis muscle force-length relationship in situ and properties ex vivo. We hypothesized that the human gracilis would have a functional fiber length of about 23 cm, based on the anatomical literature, and a specific tension of 225 kPa, based on the physiological literature. Data are provided as mean±standard deviation of the mean. Twelve subjects (7 males, average age 54±12 years). In situ passive and active tension were directly measured using a buckle force transducer (BFT) placed on the distal gracilis tendon. Passive tension was measured in each of four joint configurations (JC) prior to muscle stimulation, and, to produce active tension, the anterior branch of the obturator nerve was stimulated. The muscle was progressively lengthened by extending the knee and abducting the hip. Since we could not measure optimal fiber length directly in our subjects during isometric testing we used a functional surrogate for optimal fiber length, the full-width at half-maximum (FWHM) defined from their force vs. length relationship. The FWHM is the width of the active force vs. muscle length curve at half the maximum force. A linear relationship between FWHM and optimal fiber length has been established across several mammalian species and muscles. Thus, to calculate FWHM, we fit each patient’s calculated fully active force vs. muscle length data to a quadratic curve and then calculated width at half the calculated maximum force from the equation. Optimal fiber length was then calculated from the previously established linear relationship between FWHM and optimal fiber length. Each subject’s PCSA was calculated from their muscle volume and optimal fiber length.From these experimental data we established a human muscle fiber-specific tension of 171±84 kPa (n=12). We also determined the average gracilis optimal fiber length was 12.9±3.3 cm (n=12). Surprisingly, these fiber lengths were about half of the previously reported optimal fascicle lengths of 23 cm. Thus, the long gracilis muscle appears to be composed of relatively short fibers acting in parallel that may not have been appreciated based on traditional anatomical methods. We thus suggest that the value of 171 kPa be considered the best current estimate of human muscle specific tension. This work was supported the Department of Veterans Affairs grant 1 I01 RX002462 and, in part, by Research Career Scientist Award Number IK6 RX003351 from the United States (U.S.) Department of Veterans Affairs Rehabilitation R&D (Rehab RD) Service. Pilot projects leading to this protocol were supported by the Shirley Ryan AbilityLab Catalyst Grant Program, National Science Foundation Graduate Research Fellowship under Grant No. 1255833 and the Mayo Clinic Graduate School. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Direct intraoperative measurement of isometric contractile properties in living human muscle.

Skeletal muscle's isometric contractile properties are one of the classic structure-function relationships in all of biology allowing for extrapolation of single fibre mechanical properties to whole muscle properties based on the muscle's optimal fibre length and physiological cross-sectional area (PCSA). However, this relationship has only been validated in small animals and then extrapolated to human muscles, which are much larger in terms of length and PCSA. The present study aimed to measure directly the in situ properties and function of the human gracilis muscle to validate this relationship. We leveraged a unique surgical technique in which a human gracilis muscle is transferred from the thigh to the arm, restoring elbow flexion after brachial plexus injury. During this surgery, we directly measured subject specific gracilis muscle force-length relationship in situ and properties ex vivo. Each subject's optimal fibre length was calculated from their muscle's length-tension properties. Each subject's PCSA was calculated from their muscle volume and optimal fibre length. From these experimental data, we established a human muscle fibre-specific tension of 171kPa. We also determined that average gracilis optimal fibre length is 12.9cm. Using this subject-specific fibre length, we observed an excellent fit between experimental and theorical active length-tension curves. However, these fibre lengths were about half of the previously reported optimal fascicle lengths of 23cm. Thus, the long gracilis muscle appears to be composed of relatively short fibres acting in parallel that may not have been appreciated based on traditional anatomical methods. KEY POINTS: Skeletal muscle's isometric contractile properties represent one of the classic structure-function relationships in all of biology and allow scaling single fibre mechanical properties to whole muscle properties based on the muscle's architecture. This physiological relationship has only been validated in small animals but is often extrapolated to human muscles, which are orders of magnitude larger. We leverage a unique surgical technique in which a human gracilis muscle is transplanted from the thigh to the arm to restore elbow flexion after brachial plexus injury, aiming to directly measure muscles properties in situ and test directly the architectural scaling predictions. Using these direct measurements, we establish human muscle fibre-specific tension of ∼170kPa. Furthermore, we show that the gracilis muscle actually functions as a muscle with relatively short fibres acting in parallel vs. long fibres as previously assumed based on traditional anatomical models.

Investigation on Shrinkage Characteristics of Polyester-Fiber-Reinforced Cement-Stabilized Concrete Considering Fiber Length and Content

Polyester-fiber-reinforced cement-stabilized concrete is widely adopted to prevent the shrinkage cracking in pavement engineering. However, the effects of fiber length and content on the dry shrinkage and temperature shrinkage are not clear. The relationship between shrinkage resistance and strength is also discussed scantily. Hence, five types of polyester fiber length (1 cm, 3 cm, 5 cm, 7 cm, and 9 cm) and six types of polyester fiber content (0.1‰, 0.3‰, 0.5‰, 0.7‰, 0.9‰, and 1.1‰) were selected to prepare the fiber-reinforced cement-stabilized concrete. The dry shrinkage coefficients and temperature shrinkage coefficients were used to evaluate the shrinkage resistance. Moreover, the relationships among these shrinkage coefficients, compressive strength, and splitting strength at different curing ages were investigated to realize the prediction of shrinkage resistance of polyester-fiber-reinforced cement-stabilized concrete. This study aimed to seek the optimal fiber characteristics and conveniently evaluate the shrinkage resistance for the polyester-fiber-reinforced cement-stabilized concrete. Results show that: increasing the content of polyester fiber can significantly improve the shrinkage resistance of cement-stabilized concrete, especially for the temperature shrinkage. The fiber length should not be too long, especially for dry shrinkage. The optimum fiber content and fiber length is 0.7‰ and 5 cm for the dry shrinkage resistance and 0.7‰ and 9 cm for the temperature shrinkage resistance. There was higher correlation between compressive strengths and shrinkage coefficients, while the correlation between splitting strength and shrinkage coefficients was not obvious.

Study on fracture performance and failure mechanism of hydraulic basalt fiber asphalt concrete by considering temperature effect

An asphalt concrete anti-seepage core wall may be faced with the risk of cracking due to problems like uneven settlement of the foundation during the service period. Considering that hydraulic asphalt concrete (HAC) has a high asphalt content while basalt fibers have excellent tensile properties and good compatibility with asphalt, adding basalt fibers into HAC may potentially form a useful material for hydraulic engineering. Therefore, it is of great significance to comprehensively examine the fracture properties of this new composite material from both macroscopic and mesoscopic perspectives. To explore the effect of basalt fibers on the fracture performance of HAC, an experimental study was carried out on hydraulic basalt fiber asphalt concrete (HBFAC) under different temperatures by considering 3 fiber lengths and 4 fiber contents. The results showed that, when the temperature remained constant, the fracture load, fracture toughness and fracture energy of HAC all exhibited an upward trend with the increase of fiber content, and reached the maximum values at the fiber content of 4‰. Of different fiber lengths, the maximum fracture load, fracture toughness and fracture energy were observed at the fiber length of 6 mm. With the growth of temperature, the fracture load and fracture toughness exhibited a decreasing trend, while the fracture energy showed an increasing trend. At the same time, the increase in fracture load and fracture toughness due to the fiber reinforcing effect was gradually enlarged, but the increase in fracture energy was gradually reduced. Overall, the optimum fiber length and fiber content were determined to be 6 mm and 4‰, respectively. Subsequently, the fiber properties were further investigated with the discrete element method, and the results of internal mesoscopic mechanical behavior, crack development and particle displacement indicate that basalt fibers play a positive role in dispersing stress and inhibiting crack development so as to improve the toughness and cracking resistance of HAC. Finally, the failure mechanism of HBFAC at different temperatures was revealed from a mesoscopic level. The outcome of this paper provides a theoretical basis for the research and application of basalt fibers in HAC.

Strain and Strain Rate Tensor Mapping of Medial Gastrocnemius at Submaximal Isometric Contraction and Three Ankle Angles.

The aim of this study is to analyze the muscle kinematics of the medial gastrocnemius (MG) during submaximal isometric contractions and to explore the relationship between deformation and force generated at plantarflexed (PF), neutral (N) and dorsiflexed (DF) ankle angles. Strain and Strain Rate (SR) tensors were calculated from velocity-encoded magnetic resonance phase-contrast images in six young men acquired during 25% and 50% Maximum Voluntary Contraction (MVC). Strain and SR indices as well as force normalized values were statistically analyzed using two-way repeated measures ANOVA for differences with force level and ankle angle. An exploratory analysis of differences between absolute values of longitudinal compressive strain (Eλ1) and radial expansion strains (Eλ2) and maximum shear strain (Emax) based on paired t-test was also performed for each ankle angle. Compressive strains/SRs were significantly lower at 25%MVC. Normalized strains/SR were significantly different between %MVC and ankle angles with lowest values for DF. Absolute values of Eλ2 and Emax were significantly higher than Eλ1 for DF suggesting higher deformation asymmetry and higher shear strain, respectively. In addition to the known optimum muscle fiber length, the study identified two potential new causes of increased force generation at dorsiflexion ankle angle, higher fiber cross-section deformation asymmetry and higher shear strains.

Effects of Fibre Length on the Physical Properties of Oil Palm Empty Fruit Bunch Cement Board (OPEFB-CB)

In a cement board (CB) composite, fibres reinforce the board. It is because the length of the fibres significantly impacts the strength of the CB composite. Nonetheless, the physical properties of the CB are also an important aspect when dealing with the quality control of the final product. This study investigates the effects of various fibre lengths in CB fabrication on its physical properties, including the cement-hydration rate, tensile strength, density stability and thickness swelling (TS). Oil palm empty fruit bunch (OPEFB) fibres at different lengths are used based on the mesh retained size of R7M, R14M, and R30M. The OPEFB-CB mixture used in this research is 3:1 (cement: fibre ratio), with a target density of 1,300 kg/m3. The sample is compressed using a 1000 psi cold-compression load to achieve the desired composite thickness of 12 mm. This research revealed that the longest fibres retained on the R7M mesh with an average length of 5 mm resulted in lower density and the highest TS value. Meanwhile, lower dimensional stability was achieved by OPEFB-CB composites using fibre that retained on the R14M and R30M, having an average length of 3 mm and 1 mm, respectively. Based on the results, the optimum fibre length recommended in the fabrication of OPEFB-CB composites is processed fibres retained on the R14M sieve with an average length of 3 mm. This recommendation is made based on the most stable density and lowest TS results achieved by the R14M retained fibres which is in the range of 1,231–1,309.4 kg/m3 and TS of 0.65 %.

Coupling effect of fiber reinforcement and MICP stabilization on the tensile behavior of calcareous sand

Coupling method of fiber reinforcement and microbial induced carbonate precipitation (MICP) stabilization was adopted to improve the tensile behaviors of calcareous sand. Three types of fibers, including polypropylene fiber (PF), carbon fiber (CF), and basalt fiber (BF), were used to prepare fiber-reinforced MICP-stabilized calcareous sand samples with various fiber contents and lengths. Direct tensile tests were conducted on a specially designed 8-shaped sample to evaluate the tensile behaviors of the samples. Experimental results revealed that the coupled use of fiber reinforcement and MICP stabilization technique could significantly improve the calcareous sand tensile behaviors. By adding the fibers of PF, CF, and BF, the maximum tensile strength of the sample was increased by 234.0%, 111.8%, and 100.7%, and the corresponding maximum residual strength reached 26.8 kPa, 30.63 kPa, and 50.7 kPa, and their maximum failure displacement was increased by 121.2%, 95.4%, and 100%, respectively compared to the MICP stabilized sample. The coupling mechanism was attributed to the fiber inclusion promoting the calcium carbonate precipitation and forming more effective and extra-effective bonding. The interfacial shear resistance between fibers, calcium carbonate, and calcareous sand and the bridging performance of the crossing fibers facilitated the coupling effect. For all three types of fibers, the higher the fiber content, the greater the tensile strength, residual strength, and failure displacement. The tensile behaviors varied due to the difference in surface properties and mechanical properties of the fiber. PF had the best reinforcement performance on tensile behavior. For the sample with PF (0.1% fiber content), the optimal fiber length was 6 and 9 mm. Moreover, a theoretical relationship between the tensile strength increment and fiber content or fiber length was established. The results of this study are of some significance for the stability and safety of coastal engineering.

The Theoretical and Experimental Study on High Power Quasi Single Mode Tm-Doped All-Fiber Laser at 1908 Nm

Thulium-doped all-fiber lasers at wavelength of 1908 nm have developed rapidly because of more applications. In this paper, a quasi single mode thulium-doped quasi single mode all-fiber laser is reported, which can generate laser powers of 30.8 W in oscillator and 83.5 W in amplifier at wavelength of 1908 nm. The slope efficiencies are 43.93% and 55.65%, respectively. Besides, the effect of active fiber length on the conversion efficiency are studied theoretically and experimentally. The results show that optimal fiber length could improve the cross-relaxation process and pump utilization. Based on the thermal conduction equations, experiments theoretically study the cooling temperature and the coefficient of convective heat transfer impacted on thermal management to obtain high laser power output.

Influence of Different Lengths and Volumes of Basalt Fibre on Mechanical Properties of Concrete

In this research work, the influence of basalt fiber lengths and volumes on mechanical properties of concrete such as compressive strength, flexure strength and split tensile strength are studied. 12 and 24 mm lengths of basalt fiber having the same diameter (13 µm) were used in the experimental work. The influence of 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.4% and 0.5% volume of basalt fiber on mechanical properties of concrete have been studied. The results of conventional concrete and basalt fiber reinforced concrete were compared. Normal strength concrete M30 grade was considered in the work and the mechanical properties were measured at 3, 7 and 28 days of hydration period. The experimental investigation shows that high dosage of fibers creates workability problems such as mixing, clumping and balling effects. Experimental results show that there is no improvement in the compressive strength of concrete when basalt fibers were added in plain concrete mix at all ages of concrete. Moreover, the compressive strength values become unstable when basalt fibers are added to concrete. Maximum value of split tensile strength and flexure strength was obtained for 0.35% (9.275 kg/m³) basalt fiber content for both 12mm and 24mm length of basalt fiber at all ages of concrete. Comparing both 12mm and 24mm basalt fiber lengths, the 24 mm length of fiber has shown superior performance in relation to flexure strength and split tensile strength. Overall, the optimum length of basalt fiber is 24 mm and the optimum volume fraction of basalt fiber is 0.35%.

Optimizing choice of polypropylene fiber geometry for preventing spalling of high performance concrete due to fire

This article presents a work on optimization of choice of polypropylene fiber dosage and geometry to ensure thermal stability of high performance concrete subjected to fire. Three cementitious materials with different granular skeletons containing polypropylene fibers are studied. Experimental campaign of fire tests is conducted on uniaxially compressed concrete prisms via mobile gas furnace. Then, thermo-mechanical simulations are accomplished to validate experimental findings. Results show that an optimal PP fiber length should be selected in accordance with aggregate size. PP fiber diameter has shown to have no significant influence on spalling prevention.

Study of the reabsorption effect on the ytterbium-doped fiber amplifiers

In this paper, the rate equation of ytterbium (Yb) ion concentration in the upper level and the transmission equations of seed signal, pump, and amplified spontaneous emission (ASE) in the Yb-doped fiber amplifier are solved simultaneously by the explicit Runge–Kutta method. Finally, a full seed signal power spectrum simulation with the range of 1000–1130 nm is achieved. This paper focuses on the amplification of seed signals at different peak wavelengths in different Yb-doped fiber lengths. The main works are as follows: By constructing a 3D data structure of the seed signal, a parallel computing work on the propagation process of Gaussian-lineshape seed spectrum with a peak wavelength of 1000–1100 nm in Yb-doped fiber with a length of 1–30 m has been done, which significantly reduces the calculation time. Furthermore, the accuracy of calculation results has been improved by the iterative method. Finally, the reabsorption effect on the seed signals at different peak wavelengths and the competition between the seed signal and ASE have been analyzed in both single-mode and large-mode-area fibers, and the optimal gain fiber length corresponding to the different peak wavelengths of the seed signal has also been discussed.

Effect of fibrillation degree of empty fruit bunch fiber on sandwich composite incorporate with spent mushroom substrate

Sandwich composite panel for heat insulation application were fabricated from two types of agricultural biomass waste, the oil palm empty fruit bunch and spent mushroom substrate. These agricultural biomasses are abundant, renewable, and without proper disposal management, might cause massive environmental pollution. This study investigated the effect of fibrillation degree on EFB fiber through the morphology modification to enhance the properties and thermal characteristic of the sandwich composite panel. Fibrillation is a physical changes that occurred on the surface and internal structure of fiber after undergo excessive physical modification by using refiner machine. Higher fibrillation degree could be achieve by narrowing the space area between two disks of refiner which also known as refining gap. In this research, a composite panel was developed from (SMS) and (EFB) fiber via sandwich hot pressing method. One composite sample using raw EFB fiber and three composite sample at fibrillation degree 191.40%, 211.70% and 271.68% were made at density 0.8 g/cm3. Based on result, the morphological structure of EFB fiber improved in term of formation of small fibril formation, larger surface area, optimum fiber length, optimum fiber diameter and better fiber distribution in composite panel. The mechanical properties of composite was obtained at range 2.77–7.21 MPa for tensile strength, 16.61–18.59 MPa for flexural strength, 2.06–3.18 MPa for internal bond and 4.35–15.79 kJ/m2 for impact strength. For physical properties, value of water absorption and thickness swelling were obtained at range 90.34–142.61% and 18.01–44.80%, respectively. Last but not least, the thermal conductivity value of sandwich composite was obtained at range 0.234–0.282 W/m.K. Overall result found that increasing fibrillation degree on EFB fiber at 211.70% able to contribute in improving the mechanical properties, physical properties and thermal characteristic of sandwich composite panel. This research finding suggested that enhancement of fiber morphology using fibrillation degree approach is considered as an alternative eco-friendly method that could be implemented to improve the properties and thermal characteristic of sandwich composite panel.

Experimental investigation on dynamic characteristics of fiber-binder modified subgrade filler after freezing-thawing under cyclic loading

To examine the dynamic stability of fiber-binder modified subgrade filler (MSF), the dynamic triaxial test of MSF is carried out under the long-term cyclic loading after the freeze–thaw cycle. This paper describes the relationship between cumulative plastic strain (CPS) and the number of loading cycles (NLC) changing with different fiber contents, fiber lengths, additions of binder material, and freeze–thaw cycles. The critical dynamic stress under various influencing factors is determined by the numerical fitting method, and the critical dynamic stress model of MSF with multi-factor change is established. Then the normalized dynamic strength mechanical model is proposed by analyzing the normalized characteristics of dynamic strength concerning static strength. It is found that the MSF is brittle failure, the relationship between CPS and loading cycles before failure is roughly linear, and the shape of the curve after failure is approximately exponential. Compared with unmodified subgrade filler, the CPS resistance of MSF is significantly improved. The dynamic stress level required for the failure of MSF increases with fiber length and the addition of binder material increasing, and there is an optimum fiber length of 12 mm corresponding to the maximum cumulative deformation resistance. The improvement measures could improve the freeze–thaw resistance of the subgrade filler. After three and nine freeze–thaw cycles, the dynamic stress intensity of the MSF increased by 1.9 and 2.4 times compared with the unmodified filler. The proposed critical dynamic stress mechanical model of MSF provides an effective method and reference basis for controlling the long-term cumulative deformation of the railway subgrade in seasonally frozen soil regions. The normalized strength model of failure strength for MSF varying with the NLC is helpful to quickly judge the dynamic stress level required for the subgrade failure within a given number of train loads.

Effect of Polypropylene Fiber on the Unconfined Compressive Strength of Loess with Different Water Content

Fiber-reinforced soils have been of great interest to experimenters for building foundations’strength performance, time, and economy. This paper investigates the effects of water content and polypropylene fiber dosage and length on loess’s unconfined compressive strength (UCS) according to the central composite response surface design test procedure. The water content is 11%–25%, the mass ratio of fiber to soil is 0.1%–0.9%, and the fiber length ranges from 6–18 mm. The response surface method (RSM) developed full quadratic models of different variables with response values. After analysis of variance (ANOVA), the mathematical model developed in this study was statistically significant (p ≤ 0.05) and applicable to the optimization process. The optimization results showed that the optimal water content values, fiber amount, and fiber length were 16.41%, 0.579%, and 14.90 mm, respectively. The unconfined compressive strength of the optimized specimens was increased by 288.017 kPa. The research results can reference the design and construction of fiber-reinforced soil in practical projects such as road base engineering and foundation engineering.

Computationally Efficient Personalized EMG-Driven Musculoskeletal Model of Wrist Joint

Myoelectric control has gained much attention which translates the human intentions into control commands for exoskeletons. The electromyogram (EMG)-driven musculoskeletal (MSK) model shows prominent performance given its ability to interpret the underlying neuromechanical processes among the MSK system. This model-based scheme contains inherent physiological parameters, e.g., isometric muscle force, tendon slack length, or optimal muscle fiber length, which need to be tailored for each individual via minimizing the differences between the experimental measurement and model estimation. However, the creation of the personalized EMG-driven MSK model through the evolutionary algorithms is time-consuming, hurdling the use of the EMG-driven MSK model in practical scenarios. This article proposes a computationally efficient optimization method to estimate the subject-specific physiological parameters for a wrist MSK model based on the direct collocation (DC) method. By constraining control variables to the experimentally measured EMG signals and introducing the physiological parameters into control variables, fast optimization is achieved by identifying the discretized parameters at each grid simultaneously. Experimental evaluations on 12 healthy subjects are performed. Results demonstrate that the proposed method outperforms the baseline optimization algorithms used in the literature, including genetic algorithm, simulated annealing algorithm (SA), and particle swarm optimization (PSO) algorithm. The proposed DC method shows the possibility to alleviate the costly optimization procedure and facilitate the use of the MSK model in practical applications.

Upper Extremity Joint Torque Estimation Through an Electromyography-Driven Model

Abstract Cerebrovascular accidents like a stroke can affect the lower limb as well as upper extremity joints (i.e., shoulder, elbow, or wrist) and hinder the ability to produce necessary torque for activities of daily living. In such cases, muscles’ ability to generate forces reduces, thus affecting the joint’s torque production. Understanding how muscles generate forces is a key element to injury detection. Researchers have developed several computational methods to obtain muscle forces and joint torques. Electromyography (EMG) driven modeling is one of the approaches to estimate muscle forces and obtain joint torques from muscle activity measurements. Musculoskeletal models and EMG-driven models require necessary muscle-specific parameters for the calculation. The focus of this study is to investigate the EMG-driven approach along with an upper extremity musculoskeletal model to determine muscle forces of two major muscle groups, biceps brachii and triceps brachii, consisting of seven muscle-tendon units. Estimated muscle forces are used to determine the elbow joint torque. Experimental EMG signals and motion capture data are collected for a healthy subject. The musculoskeletal model is scaled to match the geometric parameters of the subject. Then, the approach calculates muscle forces and joint moment for two tasks: simple elbow flexion extension and triceps kickback. Individual muscle forces and net joint torques for both tasks are estimated. The study also has compared the effect of muscle-tendon parameters (optimal fiber length and tendon slack length) on the estimated results.