Comparative Study of Glass Fiber Content Measurement Methods for Inspecting Fabrication Quality of Composite Ship Structures

Abstract

A comparative study of glass fiber content (Gc) measurement methods was conducted using actual glass fiber reinforced plastic laminates from the hull plate of a 26-ton yacht. Two prototype side hull plates with the design Gc (40 wt.%) and higher Gc (64 wt.%) were prepared. Four methods were used to study the samples: the calculation method suggested by classification societies’ rules; two direct measurement methods using either calipers and scales or a hydrometer; and the burn-off method, wherein the resin matrix is combusted from the laminates. The results were compared and analyzed to identify the accuracy and benefits of each method. The rule calculation method was found to be effective if the quality of the manufacturing process is known. However, fabrication errors in the laminate structures cannot be detected. Additionally, while direct methods are used to measure the density of glass fibers using measurements of the densities of raw materials and laminates, the volume of inner defects occurring during the fabrication of laminates could not be considered. Finally, it was found that the burn-off method measures Gc and considers the defect volume (voids) inside laminates as well as the non-uniformity of the external shape.

Error Analysis of Non-Destructive Ultrasonic Testing of Glass Fiber-Reinforced Polymer Hull Plates

“…According to Table 4, the void content was approximately 0.92-1.80%, which is comparable to the void content of a typical hull plate [27]. A burn-off test was performed to measure the Gc values and void contents [18]. From the experimental hull plate, prototypes with dimensions size of 2 cm × 3 cm were obtained.…”

“…In general, the thickness of GFRP ship structures ranges from 5 to 10 mm, and in the cases of special purpose ships such as naval vessels, it can range from 10 to 15 mm [16]. The hull plate thickness of a ship is typically approximately 10 mm [3,17], whereas the hull plate of a yacht with a length of 15 has a thickness of approximately 15 mm [18]. The parameters that influence the GFRP hull plate thickness include the ship design elements such as the ship structure size, ship speed, and its mechanical properties, depending on the material design conditions.…”

“…The parameters that influence the GFRP hull plate thickness include the ship design elements such as the ship structure size, ship speed, and its mechanical properties, depending on the material design conditions. The mechanical properties of the hull plates are determined by the Gc or the weight percentages of the fiber and resin, and they are very important design variables [3,[18][19][20][21]. The small ship hull plates that are typically observed in fishing and recreational boats are generally produced via the hand lay-up method, and they generally have Gc values of 30-50% [22].…”

“…The thickness of each hull plate prototype was measured using a vernier caliper (HANDO Digital caliper, M500-182M), and average thicknesses of 7.72 mm (Application 1), 14.63 mm (Application 2), and 18.24 mm (Application 3) (Figure 2) were obtained. A burn-off test was performed to measure the Gc values and void contents [18]. From the experimental hull plate, prototypes with dimensions size of 2 cm × 3 cm were obtained.…”

“…The results are shown in Table 5. Given that the hull plates were fabricated using the hand lay-up method, there was a minimal deviation from the design Gc, which is a common phenomenon during the hull plate fabrication process [13,18,31]. The thickness measurement errors were calculated by comparing the thickness measurements obtained via ultrasonic testing with those obtained using a Vernier caliper.…”