Fiber Inclination Research Articles

3D mesoscale model of steel fiber reinforced concrete based on equivalent failure of steel fibers

Steel fiber reinforced concrete (SFRC) is widely used in civil engineering. Investigating the mechanical properties and failure mechanisms of SFRC materials using mesoscopic models holds significant theoretical and practical importance. The bond-slip interaction between steel fibers and the cementitious matrix is crucial, yet current computational capabilities struggle to simulate the interactions among the numerous components within concrete containing a large number of steel fibers. This paper establishes an equivalent failure model to replace the bond-slip interaction. Based on this model, a multiphase mesoscopic model (including aggregates, the interfacial transition zone (ITZ), mortar, and steel fibers) is developed to predict the mechanical properties and failure modes of SFRC. The accuracy and validity of the model are verified by comparing the simulation results with the experimental results from four-point bending tests on SFRC beams, focusing on load-displacement curves, failure modes, and crack propagation. The results indicate that under load, the ITZ at the sharp edges of large aggregates in the SFRC beam is the first to be damaged, forming microcracks. Subsequently, these cracks bypass the large particles and propagate towards weaker regions with fewer steel fibers, forming macrocracks. At this stage, the steel fibers take over the load from the cementitious matrix and limit crack propagation. The simulated crack propagation trend and crack width during the loading process of the SFRC multiphase mesoscale model match well with the experimental observations. A higher fiber content can mitigate stress concentration within SFRC beams and enhance the fiber bridging effect, significantly improving the flexural load-bearing capacity and toughness of the beams. A smaller steel fiber inclination angle can effectively inhibit the propagation of vertical cracks, thereby increasing the load-bearing capacity and toughness of SFRC beams and extending the service life of the structure.

Three-dimensional fiber patterning in the annulus fibrosus can be derived from vertebral endplate topography.

The annulus fibrosus (AF) of the Intervertebral disc (IVD) is composed of concentric lamellae of helically wound collagen fibers. Understanding the spatial variation of collagen fiber orientations in these lamellae, and the resulting material anisotropy, is crucial to predicting the mechanical behavior of the complete IVD. This study builds on a prior model predicated on path-independent displacement of fiber endpoints during vertebral body growth to predict a complete, three-dimensional annulus fibrosus fiber network from a small number of subject-independent input parameters and vertebral endplate topographies obtained from clinical imaging. To evaluate the model, it was first fit to mid-plane fiber orientations obtained using polarized light microscopy in a population of bovine caudal discs for which computed tomography images vertebral endplates were also available. Additionally, the model was used to predict the trajectories based on human lumbar disc geometries and results were compared to previously reported data. Finally, the model was employed to investigate potential disc-related variations in fiber angle distributions. The model was able to accurately predict experimentally measured fiber distributions in both bovine and human discs using only endplate topography and three input parameters. Critically, the model recapitulated previously observed asymmetry between the inclinations of right- and left-handed fibers in the posterolateral aspect of the human AF. Level to level variation of disc height and aspect ratio in the human lumbar spine was predicted to affect absolute values of fiber inclination, but not this asymmetry. Taken together these results suggest that patient-specific distributions of AF fiber orientation may be readily incorporated into computational models of the spine using only disc geometry and a small number of subject-independent parameters.

Functionally graded fibre concrete constitutive model considering fibre spacing effects and interfacial interactions

The purpose of this paper is to establish a new constitutive model for functionally graded concrete (FGC) with high fiber content, considering randomly distributed cylindrical fibers and spherical, ellipsoidal, and cubic aggregates. Considering the fiber spacing coefficient and adjusting for the reinforcing effect of the fibers, the new correction factors include the fiber orientation coefficient, the fiber inclination impact coefficient, and the fiber spacing coefficient. Moreover, the interaction between the upper and lower interfaces of the FGC and the interaction between the fibers and the matrix are also considered. The interface adopts a cohesive bond-slip model to define interface plastic damage. The interaction between the fibers and the matrix is based on the rigid body-spring concept, where the matrix block is first discretized into rigid body-spring elements, which then interact with the fibers to produce bond-slip forces. During model validation, the proposed constitutive model was introduced into Abaqus using Python code. Finite element models for FGC, including the conventional uniaxial tensile model, dog-bone model, and four-point bending model, were established. The results indicate that for the FGC numerical computation model, the critical fiber volume fraction ρs ranges between 6 % and 7 %. However, the exact value should be determined based on specific practical conditions. When ρs is within the range of 0 %–6 %, the mechanical properties of FGC, such as peak stress, tensile strength, and toughness, increase with the increase in ρs. However, when ρs exceeds 6 %–7 %, the growth trend begins to slow down. In some cases, peak stress and tensile strength may decrease with an increase in ρs. At this point, the influence of the fiber spacing coefficient must be considered. Finally, by comparing with the experimental results, it is proved that the proposed constitutive model is feasible for studying the mechanical properties of FGC.

The posterior condyle grows in the direction of the increasing posterior condylar offset and the inclination angle of the ACL changes accordingly.

The purpose of this study was to reveal the changes in the shape of the posterior femoral condyle and the morphology of the ACL, both before and after epiphyseal closure. The hypothesis of this study is that the morphological change of the posterior femoral condyle and that of the ACL may be correlated to some extent. Eighty-one patients who underwent surgery for the knee joint (meniscal repair, arthroscopic synovectomy, medial patellofemoral ligament reconstruction) between 2016 and 2021 were included in this study, 48 patients aged 13 years or under (before epiphysis closure; mean age: 10.9 (range: 7-13) and 33 patients aged over 18 years or over (after epiphysis closure; mean age: 21.7 (range: 18-30). The shape of the posterior femoral condyle was evaluated via lateral view radiographs, and the morphology of the ACL was measured via sagittal and coronal magnetic resonance imaging (MRI) images. The morphology of the posterior condyle in the lateral view radiograph in patients aged 13 and under was larger in the direction of the short axis of the femur compared with that in those aged 18 and over (p < 0.001). The mean value of the inclination angle of the anterior cruciate ligament (ACL) in the sagittal plane was significantly smaller in patients aged 13 and under (41.7° ± 3.7) than in those aged 18 and over (48.5° ± 4.2) (p < 0.001). The mean values of the inclination angle of the ACL in the coronal plane were significantly smaller in patients aged 13 and under (55.7° ± 6.4) than in those aged 18 and over (63.4° ± 4.4) (p < 0.001). This study evaluates and compares the shape of the posterior femoral condyle and the morphology of the ACL fiber before and after epiphyseal closure. The posterior femoral condyle grew posteriorly rather than longitudinally, and the inclination of the ACL fibers was thought to change accordingly. Level Ⅲ.

Anisotropic behavior in the flexural properties of aligned steel fiber UHPC produced by electromagnetic field

Improving fiber utilization efficiency emerges as a viable strategy for bolstering the flexural strength of Ultra-High Performance Concrete (UHPC). However, scant attention has been given to investigating the influence of aligned fibers on their anisotropic characteristics. The aligned steel fibers UHPC (ASF-UHPC) were fabricated using electromagnetic technology, and the fiber inclination angle was studied. The flexural behavior of ASF-UHPC was tested, and the anisotropic behavior of ASF-UHPC was revealed. The ASF-UHPC samples were divided into 3 cases. Utilizing 13 mm fibers at a volume fraction of 1.5 %, Case 1, Case 2, and Case 3 flexural strengths are approximately 2.44 times, 0.65 times, and 0.39 times that of traditional UHPC (Case 0), respectively. The significance of fiber volume fraction and length on flexural performance was highlighted through parameter analysis, demonstrating their critical role in material strength and post-peak performance. In addition, a predictive formula for ASF-UHPC flexural strength was proposed, offering valuable guidance for UHPC and structural design.

Effect of Fiber Orientation and Volume Fraction on Young's Modulus for Unidirectional Carbon Fiber Reinforced Composites: A Numerical Investigation

The modulus of elasticity of unidirectional fiber-reinforced composites greatly depends on the fiber orientation and the fiber volume fraction. This paper investigates the effects of fiber orientation and fiber volume fraction using the commercially available Finite Element Analysis (FEA) software Abaqus. Carbon fiber is the reinforcing material, while epoxy is used as the matrix. Representative Volume Element (RVE) of the unidirectional carbon fiber reinforced composites are modeled in Abaqus, and the unidirectional tensile test is simulated to determine the modulus of elasticity for different fiber orientations and fiber volume fractions. The numerical results are verified by previously published results and by experimental results. It is found that the modulus of elasticity of the composite is maximum when the fiber inclination angle is 0°, i.e., the fibers are placed along the loading direction. As the fiber orientation angle increases, the modulus of elasticity also decreases and is almost constant after 45°. A linear increase in modulus of elasticity is observed for an increase in fiber volume fraction. This model will help the researcher to select the appropriate fiber orientation and volume fraction for a specific application.

Evaluating backscattering polarized light imaging microstructural mapping capabilities through neural tissue and analogous phantom imaging.

Knowledge of fiber microstructure and orientation in the brain is critical for many applications. Polarized light imaging (PLI) has been shown to have potential for better understanding neural fiber microstructure and directionality due to the anisotropy in myelin sheaths surrounding nerve fibers of the brain. Continuing to advance backscattering based PLI systems could provide a valuable avenue for in vivo neural imaging. To assess the potential of backscattering PLI systems, the ability to resolve crossing fibers, and the sensitivity to fiber inclination and curvature are considered across different imaging wavelengths. Investigation of these areas of relative uncertainty is undergone through imaging potential phantoms alongside analogous regions of interest in fixed ferret brain samples with a five-wavelength backscattering Mueller matrix polarimeter. Promising phantoms are discovered for which the retardance, diattenuation and depolarization mappings are derived from the Mueller matrix and studied to assess the sensitivity of this polarimeter configuration to fiber orientations and tissue structures. Rich avenues for future study include further classifying this polarimeter's sensitivity to fiber inclination and fiber direction to accurately produce microstructural maps of neural tissue.

Optimization of Process Parameters to Minimize the Surface Roughness of Abrasive Water Jet Machined Jute/Epoxy Composites for Different Fiber Inclinations

Composites materials like jute/epoxy exhibit high hardness and are considered as difficult-to-machine materials. As a result, alternatives to conventional machining become essential to post-process the composites. Accordingly, due to its non-thermal nature, abrasive water jet machining has recently come to be seen as one of the most promising machining methods for composite materials. In the current study, the impact of machining parameters such as traverse speed (TS), standoff distance (SOD) and abrasive mass flow rate (MFR) on machined surface roughness (Ra) has been investigated. In addition, the optimum combination of process parameters to machine a jute fiber-reinforced polymer composite with minimum Ra is predicted. The experimental results are analyzed using Taguchi and Response Surface Methodology (RSM) approaches to determine the optimum set of process parameters to achieve the lowest roughness values. Without making any changes in the machining conditions, the optimum set of values is determined for two conditions by reinforcing the fiber with 45° inclination and 90° inclination. The results reflect the different optimum combinations for each fiber inclination. For 45° fiber inclination, to achieve the minimum Ra value, the predicted combination is TS = 30 mm/min, SOD = 2 mm and MFR = 0.35 kg/min. When the fiber inclination is 90°, the predicted optimum combination is TS = 25 mm/min, SOD = 2 mm, and MFR = 0.35 kg/min. It is evident from the results that the optimum combination will be changed according to the machining conditions as well as material properties. The results confirm the effect of fiber orientation on surface roughness. The specimen with 45° fiber inclination produces a lower Ra with an average of 4.116 µm, and the specimen with 90° fiber inclination generates a higher Ra with an average of 4.961 µm.

Theoretical Modeling of Asymmetrically Inclined Fiber Optic Displacement Sensor: A Blended Approach

ABSTRACT Mathematical modeling of Fiber optic displacement sensor (FODS) is mostly done either by analytical technique or by ray tracing method. This paper is an attempt to blend analytical technique and ray tracing method to get rid of the limitations of these two techniques by superimposing them in such a way so that one gets more efficient, generalized, and accurate mathematical modeling of FODS. Modeling the sensor geometry with asymmetrically inclined fibers is of prime importance. This modeling technique is definitely a new approach to optimize the performance parameters and design of FODS with parallel, symmetric, or asymmetric inclination of fibers.

2D or not 2D? Mapping the in-depth inclination of the collagen fibers of the corneoscleral shell

The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex three-dimensional interwoven structure, biomechanical and microstructural studies often assume that the fibers are aligned in-plane with the tissues. This is convenient as it removes the out-of-plane components and allows focusing on the 2D maps of in-plane fiber organization that are often quite complex. The simplification, however, risks missing potentially important aspects of the tissue architecture and mechanics. In the cornea, for instance, fibers with high in-depth inclination have been shown to be mechanically important. Outside the cornea, the in-depth fiber orientations have not been characterized, preventing a deeper understanding of their potential roles. Our goal was to characterize in-depth collagen fiber organization over the whole corneoscleral shell. Seven sheep whole-globe axial sections from eyes fixed at an IOP of 50 mmHg were imaged using polarized light microscopy to measure collagen fiber orientations and density. In-depth fiber orientation distributions and anisotropy (degree of fiber alignment) accounting for fiber density were quantified over the whole sclera and in 15 regions: central cornea, peripheral cornea, limbus, anterior equator, equator, posterior equator, posterior sclera and peripapillary sclera on both nasal and temporal sides. Orientation distributions were fitted using a combination of a uniform distribution and a sum of π-periodic von Mises distributions, each with three parameters: primary orientation μ, fiber concentration factor k, and weighting factor a. To study the features of fibers that are not in-plane, i.e., fiber inclination, we quantified the percentage of inclined fibers and the range of inclination angles (half width at half maximum of inclination angle distribution). Our measurements showed that the fibers were not uniformly in-plane but exhibited instead a wide range of in-depth orientations, with fibers significantly more aligned in-plane in the anterior parts of the globe. We found that fitting the orientation distributions required between one and three π-periodic von Mises distributions with different primary orientations and fiber concentration factors. Regions of the posterior globe, particularly on the temporal side, had a larger percentage of inclined fibers and a larger range of inclination angles than anterior and equatorial regions. Variations of orientation distributions and anisotropies may imply varying out-of-plane tissue mechanical properties around the eye globe. Out-of-plane fibers could indicate fiber interweaving, not necessarily long, inclined fibers. Effects of small-scale fiber undulations, or crimp, were minimized by using tissues from eyes at high IOPs. These fiber features also play a role in tissue stiffness and stability and are therefore also important experimental information.

Mesoscale numerical investigation of dynamic spalling fracture in toughness concrete

This study presents a two-phase mesoscale numerical model to investigate the dynamic spalling fracture behaviour of hybrid fibre ultra-high toughness cementitious composites (UHTCC). The model simulated the presence of random steel fibres and ductile UHTCC independently, and accurately incorporated the fibre-matrix bond-slip relationship, with carefully considering the influence of the inclination angle of the steel fibres on the pullout behaviour. Validation of the numerical model involved a meticulous comparison between numerical outcomes and results from spallation tests, encompassing strain-time and velocity-time histories, failure modes, and locations of cracking or fracture. Subsequently, the developed model was employed to analyse the impact of fibre inclination, stress wave amplitude, and waveform (based on the impulse equivalence principle) on the dynamic spalling fracture behaviour of hybrid fibre UHTCC. Evaluation of spalling fracture performance was based on both maximum velocity and pullback velocity of resulting fragments or free surfaces. Findings revealed that fibres parallel to the stress wave propagation direction exhibited optimum performance. It was also observed that stress waveforms with rectangular and sinusoidal shapes presented the highest risk of spalling fracture, while exponentially attenuated waves were comparatively safer. Additionally, stress waveforms with either rise time or duration at maximum pressure were deemed hazardous. Further, the hybrid fibre UHTCC demonstrated multiple spalling cracking/fracture behaviours under all stress waves except rectangular ones. This comprehensive exploration provided insights for the utilization of hybrid fibre UHTCC in impact engineering.

Nonlinear thermo-acoustic response and fatigue prediction of three-dimensional braided composite panels in supersonic flow

In this paper, a novel aerodynamic-acoustic coupling model to investigate the influence of aeroelastic effects on the thermo-acoustic response of three-dimensional, four-directional braided composite panel is proposed, and the fatigue life under the combined aerodynamic load and acoustic load is discussed by using a rainflow cycle counting method. Assuming that the fibers are transversely isotropic and the matrix is isotropic, the fiber inclination model was used to predict the effective stiffness matrices of the composite panels. The piston theory and Gaussian random acoustic excitation were used to simulate the aerodynamic load and acoustic load, the thermal load is assumed to be a uniform distribution in steady state, and the material properties are assumed to be independent of temperature. Based on the von-Karman strain–displacement relation, the governing equations of the panel were formulated, and the response solutions of the four sides simply supported panel were obtained using Galerkin method and Runge-Kutta method. The aeroelastic effect on the thermos-acoustic response of the braided composite panel was investigated in time and frequency domains, and the life of different load conditions was predicted. The results show that the aeroelastic not only transforms the movement form, but also affects fatigue life of the panel.

A three-dimensional meso-scale approach to the fracture analysis of ultrahigh performance concrete based on micropolar peridynamics

A three-dimensional (3D) meso-scale approach is proposed to simulate the fracture of ultrahigh performance concrete (UHPC) within the framework of peridynamics (PD). Micropolar PD, as an improved form of bond-based PD, is adopted to model the cementitious matrix. A PD constitutive model considering strain-hardening and strain-softening is introduced to simulate the mechanical behavior of UHPC. To improve the computational efficiency, a semi-discrete technique is employed to simulate the fibers. Meanwhile, to compensate for the drawbacks of the semi-discrete technique in analyzing fiber deformation, the effects of fiber inclination and end deformation on the fiber–matrix interface are incorporated into the fiber pullout model. In the analysis of cracking in UHPC, uniaxial tensile and uniaxial compressive tests were simulated to calibrate the proposed 3D PD model. Then, mode Ⅰ fracture and mixed-mode fracture of UHPC beams under three-point bending were simulated. Satisfactory agreement is achieved between PD analysis and experimental observations in terms of crack paths and load–displacement curves. Additionally, the numerical results show that the random distribution of fibers has a stronger impact on the 3D fracture surface for mixed-mode fracture compared to mode Ⅰ fracture.

Behavior of UHPC columns confined by high-strength transverse reinforcement under eccentric compression

This paper presents the experimental and analytical studies on the compressive behavior of ultra-high performance concrete (UHPC) columns confined by high-strength transverse reinforcement under eccentric compression. Nine columns including test variables of spacing, strength and arrangement type of transverse reinforcements, steel fiber content and eccentricity were tested to analyze the load-lateral deflection behavior, failure modes and carrying capacity. The experiment results showed that the deformation capacity, peak load and residual carrying capacity of UHPC columns confined by high-strength transverse reinforcement under eccentric loading were significantly better than those of ordinary-strength transverse reinforcement. Reducing the spacing of transverse reinforcement and increasing the volume fraction of steel fiber could also improve the ductility and carrying capacity of UHPC columns. Then, a mesoscale model was proposed to characterize the tensile behavior of UHPC which considered the fiber inclination, fiber-matrix interface bonding and fiber embedded length. Based on the proposed tensile model, a simplified method for calculating the carrying capacity of UHPC columns under large eccentric compression was developed, where the tensile behavior of UHPC and the confinement effect of transverse reinforcements were considered. The errors between the theoretical and test values were within 10%, indicating that this method can be used to guide the design of UHPC columns.

Experimental study of dripping, jetting and drop-off from thin film flows on inclined fibers

Gravity driven film flows on vertical fibers are known to exhibit a variety of flow dynamics including the formation of droplet trains induced by the hydrodynamic (Kapitza) and Plateau–Rayleigh instability mechanisms. Through an experimental study, it is shown how inclination of the fiber from the vertical influences these dynamics. The formation of waves, regime transitions from dripping to jetting regimes, as well as the onset of drop-off in the form of droplet detachment from the fiber are illustrated and described in dependence of the fiber inclination angle and the liquid mass flow rate. Additionally, the influence of fiber diameter and nozzle geometry on regime transitions and the onset of drop-off from the substrate are examined. It is shown that the onset of drop-off is strongly related to the transition from a regime characterized by a regular wave pattern to a regime characterized by an irregular wave pattern. It is also demonstrated that this regime transition depends not only on flow rate and fiber geometry, but also strongly on the inclination angle. Interestingly, a stabilizing effect of increasing the fiber inclination is detected for constant fiber geometry and film flow rate.

Pull-out creep of hooked-end fibre embedded in ultra-high-performance concrete

If the beneficial effects of fibre reinforcement are to be considered in design of ultra-high performance fibre reinforced concrete (UHPC) structure, an understanding of the long-term creep behaviour is essential. The flexural/ tensile properties of UHPC depend on the individual contribution of discrete fibres that control the overall tensile properties. The creep of UHPC therefore depends on the pull-out creep of individual fibres under sustained load. Very little research has been conducted on single steel fibre pull-out creep. To address this lack of understanding, the impacts of fibre embedment length, fibre embedment angle and sustained load on pull-out creep are investigated in this research. The outcomes of the research show that for hooked-end fibres, a change of embedment length does not significantly influence pull-out creep. The inclination angle (angle between loading axis and fibre-embedded axis) had a significant role in concrete breakage at the loading end (embedded end at loading side) which generally occurred during the application of sustained load. Therefore, the pull-out creep was influenced by the fibre inclination angle for concrete breakage during application of sustained load. Finally, as expected with an increase in load, fibre pull-out creep increased.

Fiber inclination model for the anti-penetration performance of a new type three-dimensional angle-interlock woven composite

This study establishes a fiber inclination model suitable for a new three-dimensional angle interlocking woven UHMWPEF/epoxy composite, and evaluates its anti-penetration performance. Specifically, the microstructural characteristics of the composite material were analyzed by CT scan images, the mesostructure model of the material was established with the help of the software TexGen, and the calculation method of the fiber volume fraction of the material was designed. The meta-software ANSYS/LS-DYNA simulated and analyzed the failure mode and stress after ballistic penetration, before verifying it with the ballistic penetration test of the composite material as the target. The results show that the fiber volume fraction of the material is calculated to be 49.5% according to the derivation formula, which is consistent with that measured in the laboratory (50%±1%). By simplifying the numerical simulation model of composite ballistic penetration with the “fiber inclination model,” the residual velocity of the projectile calculated is in good agreement with the experimental value with an error of &lt;7%. In the target penetration test, the damage patterns of the target surface and the ejection surface are similar to the numerical simulation results. In the fiber inclination model, the failure shape of the projectile penetrating the horizontal one-way plate is almost circular, while the failure shape in the inclined one-way plate is irregular with a more severe damage along the inclined direction. In both unidirectional plates the damage area of the incoming surface is smaller than that of the ejected surface. Therefore, it is valid to use the fiber inclination model established to study the penetration performance of composite materials.

Machine learning prediction of fiber pull-out and bond-slip in fiber-reinforced cementitious composites

Single fiber pull-out and fiber-matrix interfacial interaction play an essential role in understanding the mechanical behavior of fiber-reinforced cementitious composites. The present study introduces a computational model for predicting the maximum fiber pull-out force and corresponding bond slip. An extensive literature survey was performed to create a pertinent comprehensive experimental database. A total of 382 experimental data were utilized to develop and train the Artificial Neural Network (ANN) models. The model input parameters included the fiber embedded length, fiber inclination angle, fiber tensile strength, fiber length-to-diameter ratio, loading rate, water-to-cement ratio, concrete compressive strength, and fiber geometry. The model output consisted of the maximum pull-out force and corresponding slip. The results indicate that ANN with two hidden layers and 12 neurons was adequate for predicting the outputs with a mean absolute percentage error (MAPE) of less than 10%. To obtain the importance of the inputs on the outputs (the maximum fiber pull-out force and the corresponding slip), a sensitivity analysis was done based on the Milne formula on the proposed ANN. According to the results, it was found that among the eight inputs, the parameters of the geometric shape of the fibers (straight, hooked-end and spiral fibers) and fiber tensile strength have the highest effect on the outputs, with an impact percentage of 16.1 and 15.1, respectively. The mean square error (MSE) was 0.9 for the maximum pull-out force and 0.14 for slip, respectively. Overall, the proposed executed model attained reasonable predictions and could offer a data driven approach to optimizing fiber-reinforced cementitious composites.

Multi-scale fiber bridging constitutive law based on meso-mechanics of ultra high-performance concrete under cyclic loading

This study presents the meso-mechanics models of the multi-scale fiber bridging constitutive law of ultra high-performance concrete (UHPC) under cyclic loading. First, an analytical fiber pullout model was improved by considering the effect of fiber inclination angle and embedded length. Second, the flexural behavior of the UHPC with various fiber volume fractions under quasi-static loading was predicted by performing meso-mechanics-based sectional analysis. Third, the relation between a single steel fiber and the crack opening displacement amplitude (ΔCOD) under cyclic loading was simulated. Importantly, regardless of the state of the single fiber in (debonding or sliding), the evolution of ΔCOD with different inclination angles and embedded lengths could be quantitatively analyzed during a cycle. Finally, the multi-scale fiber bridging constitutive law of the UHPC under cyclic loading was obtained, and the theoretical relation for the fiber bridging stress amplitude (Δσf) and ΔCOD during the entire cycle process could be quantitatively estimated. There was a slight of deviation between the predicted and experimental results for the UHPC under cyclic loading, because the effect of the UHPC matrix on the fatigue crack was neglected. Overall, the fiber bridging theoretical analysis model for the UHPC under cyclic loading showed good agreement with the experimental data.

An energy analysis of translucent concrete embedded with inclined optical fibers

Translucent concrete (TC) is a kind of energy-efficient building envelope, which is able to transmit daylight into the interior of a building efficiently with improved thermal performance. Previous research shows that a kind of novel TC embedded with inclined optical fibers (OFs) is promising to achieve better climate-responsive transmittance and improved energy-saving potential compared with conventional TC. However, the newly proposed TC differs from traditional one in both light and heat transfer processes, and its distinctive optical and thermal performance have not been fully revealed. To bridge this knowledge gap, an improved optical and thermal model of the novel TC was developed and validated with experimental data. A parametric study was conducted to reveal the effects of optical fiber inclination angle and numerical aperture (NA) on the TC. The results show that the climate-responsive transmittance of TC can be improved by inclining OFs, and this can serve as a feasible method for TC transmittance adjustment especially when OFs with high NA values are not available or not cost-effective. The optimal optical fiber inclination angle is about 10° for a south-facing TC wall in Beijing, which is able to reduce building energy consumption by about 4.98% to 21.88% depending on the coefficient of performance (COP) of heating, ventilation and air conditioning systems.