Maximum Fiber Strain Research Articles

Intrados FRCM-strengthening of a masonry bridge: Experimental and analytical investigations

This paper will present the results of an experimental campaign aimed to study the structural behavior of solid clay brick masonry arch models strengthened at the intrados with Fiber Reinforced Cementitious Matrix (FRCM). The arch models’ peculiarities are: i) the presence of the haunching made of hydraulic lime mortar-based conglomerate, and ii) the geometry that reproduces a 1:2 scaled longitudinal section of a typical Italian railway single span bridge. The arch models are tested, imposing loading-unloading cycles to analyze the effectiveness of the strengthening system. The results are expressed in terms of failure mode, load carrying capacity and ductility, which shows the increase in the strength and displacement capacity of the strengthened model. Finally, limit analysis was performed to validate the experimental results and to assess the maximum fiber strain and the corresponding stress at the peak load.

Role of intra-lamellar collagen and hyaluronan nanostructures in annulus fibrosus on lumbar spine biomechanics: insights from molecular mechanics-finite element-based multiscale analyses.

Annulus fibrosus' (AF) ability to transmit multi-directional spinal motion is contributed by a combination of chemical interactions among biomolecular constituents-collagen type I (COL-I), collagen type II (COL-II), and proteoglycans (aggrecan and hyaluronan)-and mechanical interactions at multiple length scales. However, the mechanistic role of such interactions on spinal motion is unclear. The present work employs a molecular mechanics-finite element (FE) multiscale approach to investigate the mechanistic role of molecular-scale collagen and hyaluronan nanostructures in AF, on spinal motion. For this, an FE model of the lumbar segment is developed wherein a multiscale model of AF collagen fiber, developed from COL-I, COL-II, and hyaluronan using the molecular dynamics-cohesive finite element multiscale method, is incorporated. Analyses show AF collagen fibers primarily contribute to axial rotation (AR) motion, owing to angle-ply orientation. Maximum fiber strain values of 2.45% in AR, observed at the outer annulus, are 25% lower than the reported values. This indicates native collagen fibers are softer, attributed to the softer non-fibrillar matrix and higher interfibrillar sliding. Additionally, elastic zone stiffness of 8.61 Nm/° is observed to be 20% higher than the reported range, suggesting native AF lamellae exhibit lower stiffness, resulting from inter-collagen fiber bundle sliding. The presented study has further implications towards the hierarchy-driven designing of AF-substitute materials.

A Numerical Model for Analyzing Mechanical Slippage Effect on Crosswell Distributed Fiber-Optic Strain Measurements During Fracturing

Summary Distributed fiber-optic (FO) strain measurements have become a widely used method for monitoring and diagnosing far-field strain induced during hydraulic fracturing (HF). However, field observations have revealed that the mechanical decoupling between the fiber and the rock often happens. Despite this phenomenon, much of the current research assumes that the fiber cable remains mechanically coupled to the rock formation. To improve the accuracy and reliability of field data interpretation, it is essential to better understand the effect of fiber decoupling on strain responses. The objective of this study is to simulate strain responses while taking into account the impact of fiber slippage. In this study, we developed a numerical model that allows for accurate prediction and analysis of strain responses of crosswell distributed FO experiencing mechanical decoupling. Our model first uses the 3D displacement discontinuity method to calculate displacement fields induced by hydraulic fractures. The model then accounts for the occurrence of slippage and calculates the fiber displacement distribution with slippage effect. Additionally, the model can predict fiber strain distribution in cases where the stick-slip behavior is present. To better understand the impact of friction on strain and strain-rate signals, we conduct a sensitivity analysis. This allows us to explore the effects of different friction levels on the signals, which can be critical in achieving more accurate and reliable results. Our model results reveal several key observations. First, when fiber slippage is detected, we typically observe a broadening of the extension zone near the fracture on the strain/strain rate waterfall plots, which cannot provide a well-defined fracture domain corridor. The simulated strain rate pattern matches the field observation. Additionally, the size of the decoupling zone increases as the friction between the fiber and formation decreases. Also, the decoupling generates negative cumulative strain change after a certain period of closure. Furthermore, when the dynamic friction is smaller than the static friction, sudden strain releases appearing as sticking portions were visible in the strain/strain-rate waterfall plots, indicating the occurrence of stick-slip behavior in the fiber. We also observed that the sudden strain releases in the strain rate waterfall plot occur more frequently when the maximum fiber strain gradient is smaller. Moreover, the longer sticking portion was observed when the dynamic/static friction ratio was smaller. The key innovation of this study is the development of a forward numerical model that simulates strain responses while taking into account the coupling effect between fiber and formation. To the best of our knowledge, this is the first time that such a model has been presented. Overall, our study provides an important contribution to the field of HF monitoring by enabling a more accurate and reliable interpretation of strain signals, which can ultimately improve the safety and effectiveness of HF operations.

Flexural behavior of RC beams strengthened with steel-FRCM composite

This paper presents the results of an experimental investigation of the flexural response of reinforced concrete (RC) beams strengthened using externally bonded steel fiber reinforced cementitious matrix (steel-FRCM) composite. Steel-FRCM composite strips were bonded to the tension face of four RC beams, which were tested in four-point bending. Parameters varied were the presence/absence of the external (coating) layer of the matrix, presence/absence of U-wrap anchorages, and loading rate. Results are compared with those from single-lap direct-shear tests conducted on the same composite. The direct-shear tests showed that debonding of steel-FRCM joints is characterized by fiber slippage and fracture of the matrix layer at the internal matrix layer-fiber interface. In the beam tests, the strengthening system increased the yield load by 15–21% relative to the unstrengthened beam. The ratio of the load at which debonding occurred to the load at yielding ranged from 1.11 to 1.19 for each strengthened beam. The load rates employed and the presence of the external matrix layer did not appear to significantly affect the failure mode or the load and midspan displacement at debonding. The presence of the U-wraps helped restrain the peel-off of the composite observed in strengthened beams without the U-wrap, however, they did not restrain the fiber slippage at the ends of the composite, which inhibited composite action. Average values of the maximum fiber strain at composite debonding determined using strain profiles from strain gages, an approximate method, and moment-curvature analysis were 0.54%, 0.73%, and 0.83%, respectively.

A notched coupon approach for tensile testing of braided composites

A notched coupon geometry was evaluated as a method for tensile testing of 2D triaxial braid composites. Edge initiated shear failure has been observed in transverse tension tests using straight-sided coupons based on ASTM D3039. The notched coupon was designed to reduce the effects of edge initiated failure and produce the desired tensile failure. A limited set of tests were performed with partial pressurization of tubes to determine the transverse tensile strength in the absence of edge initiated failure. The transverse strength measured with the notched coupons was considerably higher than the straight-sided coupons, comparable to the tube results, and closer to the maximum possible strength based on maximum fiber strain. Further investigations of the effects of the observed biaxial stress state and stress concentrations in the notched geometry are needed.

Response of braided composites under compressive loading

Four triaxially braided composite architectures were tested in uniaxial and biaxial compression. Three stiffness models were compared to the experimental results. Laminated plate theory provided good stiffness predictions for architectures with low crimp angles, while a fiber-inclination model worked well for all architectures, provided the experimentally observed braid pattern was sufficiently described for the architecture with the greatest crimp angle. Axial yarn undulation was observed in two architectures which had uneven braider coverage. Using failure strains from uniaxial tests, a maximum fiber strain failure criterion was able to predict biaxial failure for the specimens tested biaxially. Failure strains in the braider yarns were significantly lower than failure strains in the axial fibers (on average −0.46% compared to −1.1%, respectively).

Reliable design failure criteria for composite chambers

This paper presents a recommendation of suitable design failure criteria for composite chambers under the multiaxial state of stress. Previous research results state that a quadratic failure criterion like the Tsai-Wu criterion does not apply to the design of composite chambers. The new work developed herein shows that those quadratic interaction formulas as well as the maximum fiber strain criterion do agree with the measured data. The appropriate failure criteria are examined with an experimental technique and the finite element method on composite chambers (cases, pressure vessels, etc.). The burst strength properties are studied using the choice of a reliable design criterion with a ply degradation approach. As compared to the in situ experimental results of the burst strength of quasi-isotropic [90/ ± 45 0 ] s , and [90/ ± 30 9 ̄ 0 ] s , carbon/epoxy laminates under biaxial stress, the proposed failure criteria in this research are suitable failure criteria with which to design composite chambers.

Strain in fibers of a lumbar disc. Analysis of the role of lifting in producing disc prolapse.

A three-dimensional nonlinear finite element model has been used to predict the strain in the disc fibers of a lumbar motion segment under various single and combined loads such as those representing symmetric and non-symmetric liftings. A progressive failure analysis also has been performed under loads representing lifting while bending to one side: assuming yield and ultimate fiber strains of 14 and 16%, respectively. Large tensile strains of about 10% in the disc fibers are predicted under the maximum loads simulating symmetric lifting. Addition of lateral bending and twisting significantly increases the maximum fiber strain to more than 20%, and hence augments the risk for disc rupture. The maximum fiber strain occurs in the innermost annulus layer at the posterolateral location. Loss of intradiscal pressure or volume has a marked diminishing effect on the magnitude of maximum fiber strain predicted under flexion loadings. Failure analysis indicates that rupture initiates in the fibers in the innermost layer at the posterolateral location. With a slight increase in the loads, rupture progresses radially to the adjacent outer layer. Further progress of rupture in the fibers toward the annulus outer periphery resulting in complete radial fissure and disc prolapse appears to require additional increase in the loads. In the presence of large intradiscal pressure, the generated partial or complete radial fissure is likely to result in annulus protrusion or disc herniation, respectively. The results of clinical, epidemiologic, and experimental studies support the failure mechanism predicted in the present study.

Progressive Failure in Carbon/Epoxy Laminates Under Biaxial Stress

Despite a number of previous investigations, the question of what criterion to use to predict ultimate failure in fiber composite laminates is still open to question, and particulary so when the overall loading involves biaxial stresses. We have addressed this question by developing a progressive failure model, and comparing the model to experiments on biaxial loading of tubular specimens of quasi-isotropic AS4/3501-6 carbon/epoxy laminates. The progressive failure model uses a modified Tsai-Wu criterion for initial ply cracking, a rule for softening the ply stiffness coefficients with continued straining, and an ultimate failure criterion. It was found that a maximum fiber strain criterion agreed very well with the experiments.

Response of Quasi-Isotropic Carbon/Epoxy Laminates to Biaxial Stress

The results of biaxial tension tests on AS4/3501-6 carbon/epoxy are presented for a quasi-isotropic [90, ±45,0]s laminate. These tests were performed using a tubular spec imen subjected to internal pressure and axial tension. The specimen design appears to minimize stress concentrations in the gage section. The measured stress-strain response shows a small but definite reduction in stiffness associated with progressive matrix failure. The failure stresses and strains are consistent with a maximum fiber strain failure criterion, and are most accurately modeled with a progressive failure model that incor porates ply stiffness changes.

Long-term reliability of layer-type tight structure cable

The long-term reliability of the optical-fiber strength in the tight structure cable is discussed from the viewpoint of residual fiber strain and prooftesting condition. The maximum fiber strain in the installed tight structure cable was evaluated as 0.05 percent experimentally as the summation of: 1) compressive strain induced by nylon jacketing; 2) added strain during cable; 3) residual strain by cable installation; and 4) thermal strain in the installed condition. Based on these measured residual strains on the typical 12-fiber cable with silicone resin and nylon-coated fiber, the required prooftest level was found to be 0.19 percent in order to guarantee the 10 000-km fiber for 25 years with failure probability less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> .