• Composites Research
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• v.36 no.2
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• pp.80-85
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• 2023

A cylindrical composite lattice structure is manufactured by filament winding. The distribution of nonuniform fiber volume fraction induced by the manufacturing process can be observed. The stiffness and buckling characteristics can be influenced by non-uniform fiber volume fraction. In this paper, the effect of non-uniform fiber volume fraction through thickness direction on the torsional buckling load of the cylindrical composite lattice structure was examined. The stiffness variation induced by the non-uniform fiber volume fraction was applied to the finite element model, and buckling analysis was performed. The variations of buckling load with variations of fiber volume fraction were compared. The non-uniform fiber volume fraction reduced the torsional buckling load of the composite lattice structure.

• Composites Research
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• v.28 no.5
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• pp.311-315
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• 2015

Measuring fiber volume fraction properly is very important in designing composite materials because the fiber volume fraction mainly determines mechanical and thermal properties. Conventional Ignition methods are effective for ceramic fiber reinforcing composite materials. However, these methods are not proper for applying to carbon fiber reinforcing composites because of the venerable characteristic against oxidation of carbon fiber. In the research, fiber volume fraction of carbon fiber composites was obtained by a thermogravimetric analysis considering oxidation characteristic of the carbon fiber and the method was compared and verified with the results from microscopic cross section images.

• Composites Research
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• v.31 no.4
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• pp.161-170
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• 2018

Cylindrical composite lattice structures are manufactured by filament winding process. The fiber volume fraction non-uniformity and resin rich layers that can occur in the manufacturing process affect the stiffness and strength of the structure. Through the cross-section examination of the hoop and helical ribs, which are major elements of the composite lattice structure, we observed the fiber volume fraction non-uniformity and resin rich layers. Based on the results of the cross-section examination, the stiffness of the ribs was analyzed through the experimental and theoretical approaches. The results show that the fiber volume fraction non-uniformity and resin rich layers have an obvious influence on the rib stiffness of composite lattice structure.

• Composites Research
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• v.34 no.2
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• pp.129-135
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• 2021

In this paper, in order to examine the effect of fiber volume fraction non-uniformity in thickness direction on the buckling load of cylindrical composite lattice structures, we modified the equation of buckling load of the cylindrical composite lattice structures proposed by Vasiliev. The thickness of each layer of the rib was varied by fiber volume fraction, and material properties were applied differently by using the rule of mixture. Also, we performed linear buckling analysis by varying the structure size, thickness, and average value of the fiber volume fraction of finite element model. Finally, by comparing the calculation results of the buckling load of the equivalent model using the modified buckling load equation and the results of the finite element analysis, we found that the fiber volume fraction non-uniformity in thickness direction can reduce the buckling load of the cylindrical composite lattice structure.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• Journal of the Korean Geosynthetics Society
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• v.14 no.4
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• pp.105-115
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• 2015

In this study, to understand mechanical characteristic of hybrid reinforced concrete by PVA-fiber 6 mm and PP-fiber 50 mm, which are organic fiber replaced macro-fiber with PP-fiber, four mixed Hybrid Organic Fibers Reinforced Concrete (HFRC) is compared with one mixed plain concrete without fiber reinforcement. Volume portion of the fibers are limited under one percent. The result presents that hybrid reinforcement of the organic fibers cannot maximize stiffness and ductility behavior of the steel fiber reinforcement. however, in comparison to plain concrete, it is confirmed that meaningful relation between toughness index and equivalent flexural strength with advanced ductility behavior. Also, in the case of concrete hybrid reinforced by organic fiber, when the volume portion of the fiber increases, ductility also increases. PP-fiber, which is macro fiber, has more effect on the flexural behavior of concrete than PVA-fiber, which is micro fiber, does. The result also shows that it decrease chloride penetration in chloride penetration test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.9
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• pp.771-777
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• 2007

In this paper, thermal expansion coefficients of fiber-reinforced composite materials are predicted by direct numerical simulation. From comparing the predicted results with experimental results, it is confirmed that direct numerical simulation gives similar results to the previously proposed methods while minimizing artificial assumptions. Additionally trend of variation in thermal expansion coefficients is investigated according to the fiber volume fraction.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.19-25
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• 2008

This study was carried out to investigate the bending strength properties of the unreinforced glulam beams and the GFRP laminated glulam beams according to the volume ratio of GFRP. The 7-layer glulam beams ($10cm(b){\times}14cm(h){\times}180cm(l)$) were manufactured, using Larch (Larix kaempferi Carr.) laminae ($2cm(h){\times}10cm(b){\times}360cm(l)$), which were dried to the moisture content of 8% and specific gravity of 0.54. GPRP of 0.1 and 0.3 cm was reinforced between the outmost layer of bottom and next layer. When the glulam beams were reinforced with GFRP at the volume ratio of 0.7% and 2.1%, respectively, the bending strength was increased by 12% and 28%, respectively, in the reinforced beams than in control glulam beams. Also, the GFRP reinforced layer of the glulam beams with GFRP laminations blocked the progression of rupture, and the unbroken part held about 90% of the bending strength. In the results of glue joints test, the block shear strength is higher than $7.1N/mm^2$, the standard of KS F3021, and in the result of delamination, the adhesive strength is good as the water soaking and boiling delamination was less than 5%.

• Journal of the Korea Institute of Building Construction
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• v.8 no.1
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• pp.43-48
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• 2008

Fifteen concrete specimens were mixed and tested to explore the significance and limitation of appling the polyvinyl alcohol (PVA) fiber and steel fiber with end hook to concrete. Main parameters investigated were volume fraction and length of the fibers. The measured mechanical properties of fiber reinforced concrete are analyzed according to the equivalent fiber amount index explaining the adding amount and length of fibers. Test results showed that compressive strength of fiber reinforced concrete was higher than that of concrete with no fiber by $10{\sim}20%$. The normalized splitting tensile strength and flexural strength of PVA fiber reinforced concrete were similar to those of concrete with no fiber, whereas those of steel fiber reinforced concrete increased with the increase of the equivalent fiber amount index. In particular, much higher ductile behavior was observed in steel fiber reinforced concrete than in PVA reinforced concrete, indicating that the slope of descending branch of load-displacement relationship of steel fiber reinforced concrete decreased with the increase of the volume fraction and length of the fiber.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.3
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• pp.40-47
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• 2021

This study investigates the influence of hooked-end steel fiber volume fraction and aspect ratio on the mechanical properties, such as compressive and flexural performance, of concrete with specified compressive strength of 30MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were selected. The flexural tests of steel fiber reinforced concrete (SFRC) prismatic specimens were conducted according to EN 14651. The compressive performance of SFRC with different volume fractions (0.25, 0.50 and 0.75%) were evaluated through standard compressive strength test method (KS F 2405). Experimental results indicated that the flexural strength, flexural toughness, fracture energy of concrete were improved as steel fiber volume fraction increases but there is no unique relationship between steel fiber volume fraction and compressive performance. The flexural and compressive properties of concrete incorporating hooked-end steel fiber with aspect ratio of 64 and 80 are a little better than those of SFRC with aspect ratio of 67. For each SFRC mixture used in the study, the residual flexural tensile strength ratio defined in Model Code 2010 was more than the limit value to be able to substitute rebar or welded mesh in structural members with the fiber reinforcement.