Trends of unique electro-micromechanical techniques have been explained and used as an efficient nondestructive evaluation (NDE) method for sensing and determination of microdamage at the filler/epoxy interface in nanocomposites. Prior research activities have developed NDE methods to identify and avoid structural damage in fiber/matrix nanocomposites. Furthermore, such detection methods have been used in place of expensive external sensors to detect damage in polymer matrix nanocomposites. Up to now, micro-mechanical and electrical resistance measurement methods have been used to sense the damage and strain induced by stresses or shape changes in conductive polymer nanocomposite materials. This “Self-sensing” method has also been used to evaluate interfacial damage in fiber reinforced polymer matrix nanocomposites. The advantages of this new NDE method include better stability, lower cost, and relative simplicity. Electro-micromechanical technique can be applied for carbon nanotube (CNT)/epoxy composites using four-point probe method with their contents. The fracture of carbon fiber is detected by nondestructive acoustic emission (AE) relating to electrical resistivity under double matrix composites (DMC) test. The damage sensitivity of fiber fracture, matrix deformation and fiber tension for CNT/epoxy composites can increase with CNT volume fraction. Reinforcing effect of CNT addition obtained from mechanical properties and apparent modulus measurements can be identified. For the concept of nondestructive evaluation, damage sensitivity and reinforcing effect of carbon nanocomposites can be obtained from the electrical resistivity measurement with AE.

Since the anti-icing on the topcoat layer of the aircraft or mobility systems can be a factor leading to functional failures or accidents, material engineering to prevent icing involves creating hydrophobic surfaces. Interfacial adhesion and electrical properties of polyurethane (PU)-type aircraft topcoat layers for anti-icing and lightning strike protection (LSP) were evaluated by 2D electrical resistance (ER) mapping with different oxidation times. Multi-wall carbon nanotubes (MWCNT) were treated using hydrogen peroxide to improve dispersion. Mechanical property of MWCNT/PU topcoat was determined via thin film tensile test. Static contact angle was measured to evaluate work of adhesion between MWCNT and PU coating layer. Interfacial adhesion between MWCNT and PU coating layer was obtained via pull-out test and were consistent with different MWCNT oxidation times. Electrical properties of MWCNT/PU topcoats were evaluated by surface ER. Higher tensile strength of MWCNT/PU topcoat could contribute to higher interfacial adhesion. Some anti-icing outcomes for aircraft topcoat were also introduced comparing with LSP result. It was also confirmed that the method of controlling the structure of polymers using solvents to adjust surface hydrophobicity and ice prevention effects is effective. PU topcoats are primarily used on the exterior of recent mobility device. Changes in the curing enthalpy and crystal structure were observed with adjusting the ratio between PU and xylene, which led to improve tensile strength. Changes in surface energy and contact angle occurred depends on xylene content, and de-icing of PU topcoat was enhanced with the surface of the xylene PU topcoat compared to the neat PU topcoat. It was considered that manipulating the polymer structure via different solvent amounts in topcoats could be used as an innovative technique in hydrophobic surface for anti-icing.

Trends of unique electro-micromechanical techniques have been explained and used as an efficient nondestructive evaluation (NDE) method for sensing and determination of micro-damage at the filler/epoxy interface in nanocomposites. Prior research activities have developed NDE methods to identify and avoid structural damage in fiber/matrix nanocomposites. Furthermore, such detection methods have been used in place of expensive external sensors to detect damage in polymer matrix nanocomposites. Up to now, micro-mechanical and electrical resistance measurement methods have been used to sense the damage and strain induced by stresses or shape changes in conductive polymer nanocomposite materials. This “Self-sensing” method has also been used to evaluate interfacial damage in fiber reinforced polymer matrix nanocomposites. The advantages of this new NDE method include better stability, lower cost, and relative simplicity. Electro-micromechanical technique can be applied for carbon nanotube (CNT)/epoxy composites using four-point probe method with their contents. The fracture of carbon fiber is detected by nondestructive acoustic emission (AE) relating to electrical resistivity under double matrix composites (DMC) test. The damage sensitivity of fiber fracture, matrix deformation and fiber tension for CNT/epoxy composites can increase with CNT volume fraction. Reinforcing effect of CNT addition obtained from mechanical properties and apparent modulus measurements can be identified. For the concept of nondestructive evaluation, damage sensitivity and reinforcing effect of carbon nanocomposites can be obtained from the electrical resistivity measurement with AE.

As the demand for fiber-reinforced composite (FRC) has increased in various industries, composite materials have been manufactured in larger sizes and more complex shapes. Since the FRC has been manufactured in such larger and more complex shapes, wettability, one of the important factors in FRC manufacturing efficiency, has been the focus of many researchers. This paper explores various evaluation methods of the wettability between fiber and polymer matrix. Generally, work of adhesion, capillary, and permeability methods have been used to evaluate the wettability parameters between the fibers and the polymer matrix. These three parameters exhibit different scales of measurements such as surface energy, viscosity of the polymer, the fiber volume fraction, fiber orientation, and so on. Future research may include complementary studies between these evaluation methods.

Adhesion of hybrid composite materials is essential in the manufacture of wind turbine blades. In the case of huge composite structures, however, the adhesive section between hybrid composite (GFRP, CFRP) was too thick, and it could be lead to decrease adhesion peroperty. In this research, adhesive properties were investigated with different adhesive thicknesses for glass fiber and carbon fiber reinforced hybrid composites. As the adhesive thickness increased, the lap shear strength (LSS) decreased in a rather exponential function. In addition, there were problems that as the thickness of the adhesive increases, voids easily formed inside the adhesive, and the thick adhesive layer had low resistance to bending. Even when the thick bonding section was formed with GFRP addition, added GFRP was deformed more in the bonding part upon the applied external stress. This could be because the interfacial stress was greater than that of the neat epoxy adhesive. It was monitored by 3D electrical resistance (ER) mapping of the CFRP substrate was used to evaluate the shear stress transfer of the bonding part and the CFRP substrate. The addition of GFRP to the epoxy adhesive can improve the adhesion and the resistance to shear failure for thick adhesive parts, such as wind turbine blades (WTB).

For improvement of mechanical property and manufacturing efficiency of fiber reinforced composites, wettability, which was affected by temperature, viscosity, the pressure of resin injection, fiber volume fraction, fiber array, and so on, was important factor, which had been focused many researchers. Although the wettability during manufacturing processing was usually evaluated by the permeability, it does not contain the surface energies for the fiber and matrix. Using innovative CF tow capillary glass tube method (TCGTM), this study investigated the wetting, wicking and interfacial properties for three type CFs reinforced epoxy composites combined with a triple-fiber fragmentation test. The CFs TCGTM was performed to evaluate wettability and wicking of CF tow with epoxy resin by measuring height of impregnated epoxy front in capillary tube more practically. After curing the specimens, contact angle between CF and epoxy was measured using FE-SEM photos directly. Wetting and wicking were also evaluated by measuring the impregnated length of epoxy droplets on CF tow, and compared with result by CF TCGTM. From all of the relating tests, the 50C type CF exhibited better wetting and wicking than 60E type CF and the desized CF. Interfacial shear strength (IFSS) were evaluated using a triple-fiber fragmentation test for three different type CFs. Better IFSS of the 50C type CF was consistent with wetting and wicking results by CFs TCGTM. A new innovative CF TCGTM can be applicable for conventional CF reinforced epoxy composites more practically by combining with micromechanical test for the IFSS between single CF and epoxy mainly.

This study improved the interfacial and mechanical properties of carbon fiber (CF) reinforced 5-ethylidene-2-norbornene (ENB) composites using the Ru catalyst coating method on CF for vacuum-assisted resin transfer molding (VARTM). Generally, the Ru catalyst added ENB was polymerized using mixing two materials. The interfacial and mechanical properties of the composites containing Ru catalyst coated carbon fabric were higher than those in which Ru catalyst was mixed in the ENB before being embedded in the CF fabric. It can be mainly due to the uniform or random dispersion of Ru catalyst by two different manufacturing processes. The interfacial properties determined using the microdroplet test, e.g., the surface energy and work of adhesion, Wa, were consistent with macro-mechanical properties. From the T-peel test combined with electrical resistance (ER), the Ru catalyst coated CF fabric/ENB composite responded reasonably well with high peeling strength. The different Ru catalyst processing methods resulted in different interfacial, mechanical, and electrical sensing properties, with the Ru catalyst coated CF composites typically having better properties. This study is about the Ru catalyst coated CF fabric, which can be applied to manufacture geometrically complex and large structural composites and will help improve product manufacturing efficiency and quality.

Composite materials for vehicle parts require lightweight, high strength and good impact properties. In this study, the optimized manufacturing conditions of epoxy foam (EF) were investigated to improving mechanical performance of carbon fiber reinforced plastic (CFRP)/EF/CFRP sandwich composites for vehicle parts such as impact, flexural property. The optimal curing temperature was found to be 60 °C, by measuring the reaction rate, volume increase rate, density, cell size, glass transition temperature, and specific compressive strength of the EF. In addition, foams after 180 °C thermal aging were observed, and the properties of the EF cured at 60 °C were the most stable under the thermal aging. The performance of the sandwich EF composites was investigated using compressive, flexural strength, lap shear strength, and impact tests. The optimized cell condition of the EF was correlated to improving interfacial adhesion of sandwich composite.

The evaluation of interfacial properties between fiber and epoxy resin is very important. An advanced microdroplet pull-out test was introduced to quantitatively evaluate the interfacial adhesion. To improve the interfacial property, dopamine was added in the epoxy resin whereas grease treatment was applied to the glass fiber to reduce the interfacial property. The pull-out forces of microdroplets as well as acoustic emission energy were measured by establishing a relationship between the adhesive force and acoustic emission energy per embedded length. Microdroplet fatigue tests were performed on microdroplets with the same embedded lengths. To observe the effect of interfacial properties, tensile specimens of milled glass fiber-reinforced epoxy composite were manufactured and tensile tests were conducted. During this tensile testing, the stress distribution was determined using polarized optical light. The results indicated that the dopamine conditions produced the highest degree of curing of the epoxy resin resulted in improved mechanical properties and interfacial shear strength. In addition, the studies also demonstrated that the debonding and fracture forces of the microdroplets were proportional to the acoustic emission energy accompanying fracture of specimens during microdroplet pull-out test with the associated acoustic emission test.

This study investigated the effect of activated bamboo charcoal (ABC) for improving thermal and interfacial properties in carbon fiber (CF) reinforced epoxy. Two manufacturing methods, vacuum assisted resin transfer molding process (VARTM) and resin film injection (RFI) processes were compared. Tensile and flexure properties of ABC added epoxy (EP), with different ABC weight fractions were evaluated. Comparative dispersion of ABC was evaluated using two dimensional (2D) electrical resistance (ER) and weight mappings for two manufacturing processes. Specimen using RFI process exhibited more stable ER than VARTM. Both interlaminar and interfacial shear strengths (ILSS & IFSS) of the CF/ABC-EP composites were consistent. RFI process was better suited for manufacturing ABC added fiber reinforced composite than VARTM process. For both at initial case and after 30 days thermal degradation, 10 wt% ABC added CF/EP composite was determined for maximum mechanical, interfacial and thermal properties due to suitably-dispersed ABC with stress transfer uniformly.

Interfacial, electrical, and mechanical properties of polyurethane (PU)-type aircraft topcoat layers for LSP (Lightning Strike Protection) was evaluated by 2-D electrical resistance (ER) mapping with different oxidation times. Multi-wall carbon nanotubes (MWCNT) were treated using hydrogen peroxide to improve dispersion. Mechanical property of MWCNT/PU topcoat was determined via thin film tensile test, and oxidation degree was determined using TGA and EDS. Static contact angle measurements were used to evaluate work of adhesion between MWCNT and PU coating layer. Interfacial adhesion between MWCNT and PU coating layer was obtained via pull-out test and both results were consistent with different MWCNT oxidation times. Electrical properties of MWCNT/PU topcoats were evaluated by surface ER. Surface ER was the lowest at 5 days oxidation times. Higher tensile strength of MWCNT/PU topcoat could contribute to higher interfacial adhesion. Visualization was used to determine MWCNT dispersion and verified successfully using the color variation of 2D ER mapping.

Recently, composite materials contain not only good mechanical property but also they possess additional properties such as damage sensing, piezoelectricity. In this study, glass fiber reinforced composites (GFRC) containing air bubbles were manufactured by vacuum assisted resin transfer molding (VARTM) with potential uses as sound insulation. To verify the effectiveness of these bubbles for sound insulation, fragmentation testing with acoustic emission (AE) was introduced using single fiber composites (SFC). The SFC consisted of a single glass fiber which was covered with epoxy resin containing air bubbles. During the fragmentation tests, an AE sensor was installed on the SFC which detected fracture of glass fiber and measured the resulting AE amplitude and energy. In manufacture of GFRC, randomly-chopped glass fiber mats were used for collecting air bubbles in the epoxy resin. These air bubbles were relatively easily introduced into the mats. Four AE sensors were installed on the GFRC specimen to measure the wavespeed and change in amplitude. Finally, the qualitative sound pressure level (SPL) was measured to ascertain the retardation of sound by the GFRC using lab-made impedance tube which was comparative evaluation due to the allowable measurement deviation. The AE amplitude and energy resulting from fiber fracture during fragmentation were smaller in the specimen containing air bubbles than for those in neat condition specimens. In bulk tests, the SPL shielded by GFRC containing air bubbles was comparatively lower than that in the neat condition as well.

This paper describes a new type of sensor that can monitor electrical signals for external stress or damage and heat transfer. It is composed of conductive pencil lead graphite, which is sensitive, affordable and easy-to-handle. This work was to detect mechanical damages in composites using Pencil Lead Drawn Paper Sensor (PLDPS). To measure electrical resistance (ER) via bending, by narrowing the distance between glass plates attached with PLDPD, ER increased stepwise while ER decreased with widening the distance reversely. The PLDPS can easily change the shape in a rectangular vortex. ER change responded well in tensile and flexural tests, while it showed leveling off under cyclic compression. Two-dimensional ER mapping was used during impact, drilling and heat transfer tests for detecting damage and thermal transfer. Compared to strain gauges, PLDPS can be applied inexpensively to detect damages successfully under various mechanical tests.

Sensing of dispersion and adhesion of PU type aircraft topcoat layer for LSP (Lightning Strike Protection) was evaluated by 2 dimensional (2D) electrical resistance (ER) mapping with different treatment times and multi-wall carbon nanotube (MWCNT) weight fractions. Conductive MWCNT was treated using hydrogen peroxide to improve dispersion in polyurethane (PU) type paint for several days. After treatment processing, MWCNT was dispersed in PU type coating solution using sonication dispersion method. CNT/PU coating solution was applied on the aircraft surface of carbon fiber reinforced epoxy composite (CFRC) using spray method. Static contact angle was performed using 4 types of solvents to calculate the work of adhesion between CNT/PU coating layer and CFRC surface. Surface ER of MWCNT added PU coating layer was measured to determine MWCNT dispersion. Visualization of MWCNT dispersion exhibited using 2-D ER mapping, whereas adhesion between MWCNT/PU coating layer and CFRC was evaluated via cross hatched cut test. The optimized condition of MWCNT treatment time and MWCNT weight fraction was found intensively.

Electrical resistance (ER) and thermogram measurements were used to evaluate thermal transfer, interfacial and mechanical properties of carbon fiber reinforced thermoplastic polycarbonate composites. Carbon nanotubes (CNTs) were fairly uniformly dispersed in polycarbonates using a solvent dispersion method. The CNTs were then further dispersed with an additional time using a twin screw extruder. The effect of CNT on the mechanical properties of polycarbonate was evaluated using a thin film tensile test. For thermogram to evaluate the transferring temperature the composite was placed on a hotplate and copper wires were inserted in the composite at uniform thickness intervals. Due to the different inherent thermal conductivity of CNT, ER was measured to detect thermal changes in the carbon fiber/CNT-polycarbonate composites. The comparison of interlaminar shear strength (ILSS) was to investigate effects of CNT on mechanical and interfacial properties. The uniform distribution of CNTs affected all of these properties in carbon fiber-reinforced thermoplastic composite. Furthermore, heat transfer and heat release become more rapid with the addition of CNT than the without case.

Carbon nanomaterials including, but not limited to, carbon nanotubes (CNTs) and graphene have attracted considerable attention due to their nanoscale electrical conductivity. Flexible sensors have experienced a growing demand due to several potential applications, such as personalized health monitoring and robots. In this study, CNT/cellulose composite sheets were manufactured using spray methods for flexible sensors. MWCNTs were ultrasonically dispersed in an acetone solvent and flexible plain paper was used as a substrate on which the CNT suspension was sprayed. At the end of the coating process, to remove the acetone solvent, the specimens were dried in an oven. Electrical resistance (ER) three-dimensional-mapping and optical observation were used to confirm and evaluate the dispersion of CNTs on the paper. To access the wettability of CNT/cellulose sheets, the changes of static contact angle of distilled water droplets on the sheets were measured. The critical point of the CNT coating numbers was determined using the ER method as well as the change of wettability using the static contact angle measurements.

A study was performed to utilize Pencil Lead Drawn Paper Sensor (PLDPS) as a strain and damage sensor by drawing multiply Pencil Sensors on two paper types. To evaluate the optimal paper as a PLDPS substrate of two type papers, i.e., plain and Han papers were used. The stability and uniformity of the mechanical properties, were compared for the paper types. Variability of electrical resistivity (ER) was also determined using four different types of pencil lead to make the PLDPS. In the evaluation of the properties of the PLDPS, for the different pencil lead types, the pencil lead weight was determined by drawing multiple lines and the ER of neat pencil leads and PLDPS compared. Interfacial properties of the PLDPS with different pencil lead types were measured by a spreading test, which provides information on wetting and permeability properties, using double distilled water. The sensitivity and uniformity of the pencil lead paper sensors made of four different pencil leads were compared in tensile loading. Plain paper was more suitable than Han Paper for use as the substrate of PLDPS. In addition, compared to other pencil leads, 6B, which exhibited low sensitivity but high uniformity, was determined to be the most suitable pencil lead.

Composites has been an area of active research for the past several decades due to their lightweight and good mechanical properties. However, the aging of fiber reinforced composites is a major issue due to exposure of thermal, water and ultraviolet conditions. Continuous damage could bring about mechanical property degradation and damage at the interface. This is a comprehensive review on of aging effects in water, heat, ultraviolet etc. on composites and the changes in chemical, mechanical and interfacial properties, evaluated by nondestructive and micro-mechanic evaluations. It focuses particularly on composites with superior chemical, mechanical and interfacial properties, as well as good high resistance to aging, as these are considered to be important Structural materials. Types of composites and aging effects of aged composite by exposure to water, heat and ultraviolet radiation are explored. Based on these nondestructive and micro-mechanical evaluations methods are suggested to reduce the diverse ageing effects.

The evaluation of damage sensing for flexural, interfacial and fatigue conditions was studied for carbon fiber reinforces plastic (CFRP) rope, with 4 different formulations of epoxy resin. Thermal analysis and tensile tests were used to investigate the thermal and mechanical properties for different epoxy formulations. Using these experimental results along with the empirical equation between tensile strength, glass transition temperature, Tg, and enthalpy, ΔH, optimum conditions for the epoxy formulations were found. Eddy current and static contact angle measurements were made to evaluate the wettability of epoxy into the carbon fibers with the different epoxy types. Flexural strength, fatigue strength and inter-laminar shear strength (ILSS) were evaluated for manufactured CFRP rope via pultrusion process. Changed ratio of electrical resistance (ER) of CFRP rope were measure during flexural testing, for signs of micro-cracking leading up to final fracture. The signal of CFRP rope were measured by changes in electrical resistance (ER) to predict the fracture failure. From the results of these studies it was concluded that an acid anhydride-based epoxy was the optimal epoxy formulation for manufacture of CFRP rope.

Ammonium dihydrogen phosphate (ADP) as a glass fiber (GF) coating is useful as a flame retardant for glass fiber reinforced composites (GFRC). Three different ADP weight fraction coatings on GF resulted in distinctly different behavior. Single fiber tensile tests were conducted and statistically evaluated by Weibull distribution, for the three different ADP coatings. The tensile strength of neat GF and ADP coated GFs was not significantly affected by the ADP weight fraction. GFRC was manufactured using ADP coated GF mat reinforcement in unsaturated polyester (UP). The flame retardant test was used to access and compare the flame retardant property for the different composite specimens. The GFRC with the 20 wt% ADP coating exhibited the best flame retardant property. Interfacial/wettability properties were determined using static contact angle measurements. The static contact angle increased with increasing ADP weight fraction. Interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) were measure using the short beam and microdroplet pull-out tests respectively. Both ILLS and interfacial adhesion decreased somewhat in the ADP coated GF, while the flame retardant property markedly improved in GFRC, for ADP coated GF mat.