• Fibers and Polymers
• /
• v.5 no.2
• /
• pp.128-133
• /
• 2004

This paper reports the effects of bleaching of alpaca tops and dyeing of bleached alpaca tops/yarns on the quality of tops and yarns. A dark brown alpaca top was bleached with hydrogen peroxide. Two bleaching methods were tried for effectiveness of color removal. A portion of each bleached top was dyed after bleaching. Color parameters were examined for unbleached, bleached and bleached/dyed tops, these tops were then converted into yarns of different twist levels and counts using a worsted spinning system. Some of the bleached yarn from each bleaching method was dyed in a package dye vat to compare the difference of top dyeing versus yarn package dyeing on yarn quality. Fiber diameter, yarn strength, yarn evenness, yarn hairiness and fiber degradation were tested to examine the effects of bleaching and dyeing on these properties at top and yarn stages. A processing route for bleaching and dyeing alpaca fiber was recommended.

• Computers and Concrete
• /
• v.24 no.6
• /
• pp.513-525
• /
• 2019

In this work, an experimental research has been performed on Steel Fiber-Steel Reinforced Concrete (SFSRC)specimens subjected to four-point bending tests to evaluate the feasibility of mutual replacement of steel fibers and conventional reinforcement through studying failure modes, load-deflection curves, stiffness of characteristic points, stiffness degradation curves and damage analysis. The variables considered in this experiment included steel fiber volume percentage with and without conventional reinforcements (stirrups or steel fibers) with shear span depth ratios of S/D=2.5 and 3.5. Experimental results revealed that increasing the volume percentage of steel fiber decreased the creation and propagation of shear and bond cracks, just like shortening the stirrups spacing. Higher crack resistance and suturing ability of steel fiber can improve the stability of its bearing capacity. Both steel fibers and stirrups improved the stiffness and damage resistance of specimens where stirrups played an essential role and therefore, the influence of steel fibers was greatly weakened. Increasing S/D ratio also weakened the effect of steel fibers. An equation was derived to calculate the bending stiffness of SFSRC specimens, which was used to determine mid span deflection; the accuracy of the proposed equation was proved by comparing predicted and experimental results.

• Structural Engineering and Mechanics
• /
• v.64 no.5
• /
• pp.557-566
• /
• 2017

Fiber reinforced polymer (FRP) sheets are the most efficient structural materials in terms of strength to weight ratio and its application in strengthening and retrofitting of a structure or structural elements are inevitable. The performance enhancement of structural elements without increasing the cross sectional area and flexible nature are the major advantages of FRP in retrofitting/strengthening work. This research article presents a detailed study on the inelastic response of conventional and retrofitted Reinforced Concrete (RC) frames using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi-static loading. The hysteretic behaviour, stiffness degradation, energy dissipation and damage index are the parameters employed to analyse the efficacy of FRP strengthening of brick in-filled RC frames. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

• Textile Coloration and Finishing
• /
• v.22 no.4
• /
• pp.373-379
• /
• 2010

The laboratory inspection and analysis of several types of ropes such as edge tensile test, D/d tensile test and abrasion test were carried out in order to investigate the abrasion degradation by external damage and to obtain the fundamental data for measurement against the abrasion. PET ropes were socketed and evaluated under tensile testing. A yarn-on-yarn abrasion test machine has been developed to study the damage and failure associated with rubbing between fiber surfaces. The abrasion test method consists of sliding a length of interwrapped yarn against itself in a reciprocating fashion, either dry or immersed in liquid. It has also been adapted to measure yarn-on-yarn friction. The influence of spin finish on yarn friction and abrasion was investigated extensively. This study indicates that finish has a major effect not only on yarn performance but also on rope performance under the marine environment.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.4
• /
• pp.261-283
• /
• 2023

This study aimed to review the performance stability of PET (Polyethylene terephthalate) fiber reinforcing materials among the synthetic fiber types for which the application of performance reinforcing materials to fiber-reinforced concrete is being reviewed by examining short-term and long-term performance changes. To this end, the residual performance was analyzed after exposing the PET fiber to an acid/alkali environment, and the flexural strength and equivalent flexural strength of the PET fiber-reinforced concrete mixture by age were analyzed, and the surface of the PET fiber collected from the concrete specimen was examined using a scanning microscope (SEM). The changes in were analyzed. As a result of the acid/alkali environment exposure test of PET fiber, the strength retention rate was 83.4~96.4% in acidic environment and 42.4~97.9% in alkaline environment. It was confirmed that the strength retention rate of the fiber itself significantly decreased when exposed to high-temperature strong alkali conditions, and the strength retention rate increased in the finished yarn coated with epoxy. In the test results of the flexural strength and equivalent flexural strength of the PET fiber-reinforced concrete mixture, no reduction in flexural strength was found, and the equivalent flexural strength result also did not show any degradation in performance as a fiber reinforcement. Even in the SEM analysis results, no surface damage or cross-sectional change of the PET reinforcing fibers was observed. These results mean that no damage or cross-section reduction of PET reinforcing fibers occurs in cement concrete environments even when fiber-reinforced concrete is exposed to high temperatures in the early stage or depending on age, and the strength of PET fibers decreases in cement concrete environments. The impact is judged to be of no concern. As the flexural strength and equivalent flexural strength according to age were also stably expressed, it could be seen that performance degradation due to hydrolysis, which is a concern due to the use of PET fiber reinforcing materials, did not occur, and it was confirmed that stable residual strength retention characteristics were exhibited.

• Earthquakes and Structures
• /
• v.14 no.5
• /
• pp.379-388
• /
• 2018

This study aims to identify the effect of both longitudinal reinforcement details and damage level on making a decision of repairing pre-damaged bridge columns using basalt fiber reinforced polymer (BFRP) jackets. Two RC bridge columns with improper details of the longitudinal and/or transverse reinforcement were tested under the effect of a constant axial load and increasing lateral cyclic loading. Test results showed that the lap-splice column exhibited an inferior performance where it showed rapid degradation of strength before achieving the theoretical strength and its deformation capacity was limited; however, quick restoration is possible through a suitable rehabilitation technique. On the other hand, expensive repair or even complete replacement could be the decision for the column with the confinement failure mode. After that, a rehabilitation technique using external BFRP jacket was adopted. Performance-based design details guaranteeing the enhancement in the inelastic performance of both damaged columns were addressed and defined. Test results of the repaired columns confirmed that both reparability and the required repairing time of damage structures are dependent on the reinforcement details at the plastic hinge zone. Furthermore, lap-splice of longitudinal reinforcement could be applied as a key design-tool controlling reparability and restorability of RC structures after massive actions.

• Structural Engineering and Mechanics
• /
• v.72 no.6
• /
• pp.723-736
• /
• 2019

The efficacy of a technique for the rehabilitation and strengthening of RC beam-column connections damaged due to cyclic loading was investigated. The repair mainly uses epoxy resin infused under pressure into the damaged region to retrieved back the lost capacity and then strengthening using fiber reinforced polymer (FRP) sheets for capacity enhancement. Three common types of reduced scale RC exterior beam-column connections namely (a) beam-column connection with beam weak in flexure (BWF) (b) beam-column connections with beam weak in shear (BWS) and (c) beam-column connections with column weak in shear (CWS) subjected to reversed cyclic loading were considered for the experimental investigation. The rehabilitated and strengthened specimens were also subjected to similar cyclic displacement. Important parameters related to seismic capacity such as strength, stiffness degradation, energy dissipation, and ductility were evaluated. The rehabilitated connections exhibited equal or better performance and hence the adopted rehabilitation strategies could be considered as satisfactory. Confinement of damaged region using FRP sheet significantly enhanced the seismic capacity of the connections.

• Advances in concrete construction
• /
• v.16 no.4
• /
• pp.205-216
• /
• 2023

Concrete structures may become vulnerable during their lifetime due to several reasons such as degradation of their material properties; design or construction errors; and environmental damage due to earthquake. These structures should be repaired or strengthened to ensure proper performance for the current service load demands. Several methods have been investigated and applied for the strengthening of reinforced concrete (RC) structures using various materials. Fiber reinforced polymer (FRP) reinforcement is one of the most recent type of material for the strengthening purpose of RC structures. The main objective of the present research is to identify the behavior of reinforced concrete slabs strengthened with FRP bars by using near surface mounted (NSM) technique. Validation study is conducted based on the experimental test available in the literature to investigate the accuracy of finite element models using LS-DYNA to present the behavior of the models. A parametric analysis is conducted on the effect of FRP bar diameters, number of grooves, groove intervals as well as width and height of the grooves on the flexural behavior of strengthened reinforced slabs. Performance of strengthening RC slabs with NSM FRP bars was confirmed by comparing the results of strengthening reinforced slabs with control slab. The numerical results of mid-span deflection and stress time histories were reported. According to the numerical analysis results, the model with three grooves, FRP bar diameter of 10 mm and grooves distances of 100 mm is the most ideal and desirable model in this research. The results demonstrated that strengthening of reinforced concrete slabs using FRP by NSM method will have a significant effect on the performance of the slabs.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• v.y2005m4
• /
• pp.31-34
• /
• 2005

Hygrothermal aging of the laminates of $Avimid^{R}$ K3B/IM7 in $80^{\circ}C$ water was studied as a function of immersion time prior to forming microcracks. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, change in residual stresses or interfacial damage between the fiber and matrix. The times to saturation in $80^{\circ}C$ water for the laminates and the neat resin are 100 hours and 500 hours. After 500 hours aging of the neat resin in $80^{\circ}C$ water, the glass transition temperature was changed less than $1\%$ by DSC test and the weight gain was $1.55\%$ increase. After 500 hours aging, the fracture toughness of the neat resin was decreased about $37\%$ by 3-point bending test. After 100 hours aging of the [+45/0/-45/90]s K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was $0.41\%$ increase. The $80^{\circ}C$ water diffusion rate into the neat resin was faster than into the laminates. In 100 hours, the loss of the microcracking toughness of the laminates was $28\%$ of the original toughness by our own microcracking fracture toughness criterion.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.9 no.4
• /
• pp.23-30
• /
• 2005

The Hygrothermal aging of the laminates of $Avimid^(R)$ K3B/IM7 in $80^{\circ}C$ water was studied as a function of immersion time prior to forming microcracks. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, the change in residual stresses or the interfacial damage between the fiber and the matrix. The times to saturation in $80^{\circ}C$ water for the laminates and for the neat resin were 100 hours and 500 hours. After 500 hours aging of the neat resin, the glass transition temperature was changed less than 1% by DSC test, and the weight gain was 1.55% increase with the diffusion coefficient $7\times10^{-6}m/s^2$ and the fracture toughness was decreased about 41%. After 100 hours fully saturated aging of the ${[+45/0/-45/90]}_s$ K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was 0.41% increase with the diffusion coefficient $1\times10^{-6}m/s^2$. In 100 hours, the loss of the fracture toughness of the laminates was 43.8% of the original toughness by the microcracking fracture toughness criterion. Therefore, the main factor to degrade the microcracking toughness of the laminates could be the degradation of the matrix fracture toughness.