• Composites Research
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• v.16 no.5
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• pp.1-6
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• 2003

As the use of composites has become popular in recent years, the design of the composite joints has become a very important research area because the structural efficiency of the composite structure is determined by its joints, not by its basic structures. In this paper, presented comparisons of numerical results by the FAI(Failure area index) method[9] and measured data for a various geometric shapes and stacking sequence justify the validity of the FAI method. The FAI method is shown to produce very favorable comparisons with measured failure loads of mechanically fastened composite joints with the difference well within 9.96% for all II cases investigated.

• Composites Research
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• v.22 no.5
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• pp.30-36
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• 2009

The failure strengths and modes in carbon fiber reinforced polymeric composites, with two serial bolt-fastened composite joints, were investigated to evaluate the typical joint configurations of composite components. The parametric studies were performed experimentally at room temperature dry and elevated temperature wet, $82.2^{\circ}C$ on several different laminate configurations. Based on the experimental data presented, two basic load-displacements curves are observed. Each failure mode has the characteristic curve. It is showed that the bearing failure mode occurs in elevated temperature wet condition. It is analysed that the strength of bearing failure mode is not highly depending on the effective modulus of specimen. The failure strength at elevated temperature wet is decreased by the cause of interfacial deterioration between fiber and matrix with moisture absorption.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.246-249
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• 2004

When MWK (Multiaxial Warp Knitted Fabric) composites are applied for the structures, the connections of each component using mechanical fastening is needed. The local contact between the bolted joint and the composite laminates may induce high stress concentration or breakdown in the laminates for the mechanical joints. There for, it is strongly required to study the characteristics of mechanically joints of MWK composite laminates. In this study, stress analysis near the hole boundary of MWK composite laminate is conducted with various geometric factors under different loadings. In the case of multi-pin loaded MWK composite laminates, the results show that the types of loadings and geometric factors of mechanical joints have a significant influence on the joint performances.

• Composites Research
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• v.18 no.6
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• pp.9-18
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• 2005

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.269-279
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• 1997

An investigation was peformed to study the predicting the joint strength of mechanical fasteners. Bearing failure is most important failure mode for designing joint. So in this study, the prediction method in consideration with bearing failure was chosen. In the proposed method, the characteristic length is combined with the Yamada-Sun failure criterion, Tsai-Hill failure criterion and characteristic length for Tension and Compression is determined from investigation. Especially the length of compression is determined from the "bearing failure test" that newly conceived to take bearing failure into consideration. The proposed prediction method was applied to quasi-isotropic carbon/epoxy joint showing net-tension and bearing failure experimentally. Good agreement was found between the predicted and experimental result for each joint geometry.

• Composites Research
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• v.32 no.1
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• pp.37-44
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• 2019

The reinforcement effect of micro-bolt for a bonded scarf joint was investigated. Three scarf ratios of 1/10, 1/20, and 1/30 were considered to examine the effect of scarf patch configuration on joint strength. To maintain the same density of micro-bolt, 16, 32, and 48 bolts were installed in the scarf joint specimens with scarf ratios of 1/10, 1/20, and 1/30, respectively. Tests were also carried out on the joints that are bonded with only adhesive and that are fastened with only micro-bolts to obtain reference values. The average failure loads of the adhesive joints with scarf ratios of 1/10, 1/20, and 1/30 were 29.7, 39.6, and 44.8 kN, respectively. In case of micro-bolt reinforcement, the failure loads at the same scarf ratios were 28.4, 37.2, and 40.1 kN, respectively, which corresponds to 96, 94, and 90% of the pure adhesive joint failure loads. In the case of using only micro-bolts, the failure loads were only 13-25% of the average failure loads of pure adhesive joints. Fatigue test was also conducted for the joints with scarf ratio of 1/10. The results show that the fatigue strength of hybrid joints using both adhesive and microbolts together slightly increased compared to the fatigue strength of adhesive joint, but the rate of increase was small to 2-3%. Through this study, it was confirmed that the reinforcement effect of micro-bolt is negligible in the scarf joints where shear stress is dominating the failure, unlike in the structure where peel stress is dominant.