Isao Kimpara

Smart marine structures: an approach to the monitoring of ship structures with fiber-optic sensors

Prevention of serious damage of marine structures might be achieved by monitoring the loading conditions and by inspecting the structural integrity. The concept of smart structures with a fiber-optic sensor network can be applied to marine applications. There are plenty of marine structures in huge dimensions, for example, the overall length of a very large crude carrier exceeds 200 m. A fiber-optic laser-Doppler velocimeter was developed as a displacement sensor with long gage length. The optical fiber sensor has potential advantages as a structure monitoring sensor: (i) unlimited gage length, (ii) applicability to dynamic measurement and (iii) less affected by temperature. Free vibration behavior of the coupon specimen could be monitored with excellent dynamic resolution. Flexural deformation of the specimen under cyclic bending load was also monitored, and linearity and sensitivity of the developed sensor system was confirmed. An optical time-domain reflectometer (OTDR) was applied to the damage detection of composite materials in which optical fibers were embedded. Onset and location of fiber breaks could be detected by using the OTDR technique, which was applied to tensile tests of resin, and tensile and flexure tests of cross-plied GFRP. The failure strain of the optical fiber had rather wide scatter when it was embedded in the composite, and the average values also depended on the condition of embedment. Location of the failure points could be measured with sufficient accuracy.

Structural health monitoring of IACC yachts using fiber optic distributed strain sensors: a technical challenge for America's Cup 2000

In this study, we developed a health monitoring system using a fiber optic distributed strain sensor for International Americas Cup Class (IACC) yachts. Most structural components of an IACC yacht consist of an aluminum honeycomb core sandwiched between carbon fiber reinforced plastic (CFRP) laminates. In such structures, delamination, skin/core debonding and debonding between adhered members will be result in serious fracture of the structure. We equipped two IACC yachts with fiber optic strain sensors designed to measured the distributed strain using a Brillouin optical time domain reflectometer (BOTDR) and to detect any deterioration or damage to the yachts structures caused by such failures. And based on laboratory test results, we proposed a structural health monitoring technique for IACC yachts that involves analyzing their strain distribution. Some important information about structural conditions of the IACC yachts could be obtained from this system through the periodical strain measurements in the field.

Characterization of debonding energy release rate of FRP sheets bonded on mortar and concrete

A new peeling test of FRP sheets bonded on mortar and concrete was proposed to characterize the peeling strength and examine the effects of different surface treatment and primer. A simple data reduction method was proposed for the energy release rate due to peeling from the viewpoint of fracture mechanics and theory of thin membrane. The effect of surface treatment and primer was compared by energy release rate, initiation load, and maximum load. Observing energy release rate and initiation load, it was shown that there were some differences between non-primer and primer, and observing maximum load, it was shown that there were some differences among different surface treatments.

Use of advanced composite materials in marine vehicles

Abstract The use of advanced composite materials is now limited to only a small portion of the total marine use of glass fibre reinforced plastics. Since marine transportation is looking at higher speeds with the development of new vehicle forms other than the displacement type, there is a great demand to reduce structural weight for pursuing lighter marine structure. However, most empirical approaches to substitute composites for conventional metal structures have not resulted in a significant weight reduction even with the partial use of advanced composite materials. Design from first principles will give a greater chance to optimize advanced composite materials for lightest marine structure.

Finite element stress analysis of interlayer based on selective layerwise higher-order theory

In this paper, an N-layered higher-order finite element (FE) is developed for general laminated plates, which is capable of simultaneously predicting global and local stresses. The displacement continuity constraints at interlayers are approximated by introducing imaginary springs attached on the interlayers (interlaminar springs). For confirming its validity and versatility, comparative studies using numerical results by the present element are carried out, focusing on interlaminar stress evaluations. The comparative studies show that the present element is sufficiently applicable to evaluations of interlaminar stresses, if not singular, from a practical point of view.

New Data Reduction Schemes for the DCB and ENF Tests of Fracture-Resistant Composites

Proposed in this study are new data reduction schemes for the DCB test and the ENF test. The former uses the relation between normalized crack length and the cubic root of the load-line compliance. The latter uses the CSD (Crack Shear Displacement) or the CSD compliance. R-curves both in the Mode I loading and in the Mode II loading were obtained to apply those schemes to Celion 6000/PMR-15 composite system. This system showed the interlaminar fracture resistant behaviour in both modes, which means the increasing toughness as the crack propagates.

Construction of a Stochastic Macro Failure Model of Unidirectional Fiber Reinforced Composites Based on Dynamic Failure Process Simulations of Micro Failure Models

A new failure process simulation model of unidirectional fiber reinforced composite materials is introduced considering the effect of matrix shear failure as well as fiber breaks based on a shear — lag theory in which a failure can occur randomly not only in fiber elements but also in matrix elements. A stochastic static tensile failure process of unidirectional composite materials is simulated by means of a Monte Carlo method based on a repeated increment scheme using a finite difference technique.

Computational modeling for dynamic fracture process of FRP laminates under multiaxial impact loading1

Non-linear modeling for dynamic fracture process by the finite element method has been proposed to estimate the multiaxial impact strength of glass mat and glass, carbon, glass/carbon or aramid cloth laminates. The numerical results are compared with experimental data, which are obtained by instrumented drop-weight impact test and the validity of the proposed model is confirmed.