Based on multi-layer gradient threshold CFRP plates defects detection system

A new lamination theory to calculate electric current between two probes on Carbon Fiber Reinforced Plastic (CFRP) laminates is dealt with here. Unidirectional CFRP has strongly orthotropic electric conductance. When electric current is applied on a surface of a CFRP plates using two probes, the electric voltage field is uniform for thin CFRP plate and is not uniform in the cross section for thick CFRP. In the present study, a lamination theory for thin CFRP laminates is discussed first. After that, a new lamination theory for thick CFRP laminates is proposed here. The theory for thick CFRP plates adopts non-uniform electric voltage in the thickness direction. To obtain the shape of the non-uniform voltage distribution, the analytical results of a thick single-ply of the previous paper is adopted as a contribution function to calculate the effective conductance of the thick CFRP laminate. The proposed methods are applied to two cases of a thick CFRP plate, and the results are compared with the 3-D FEM results. As a result, the new lamination theory is proved to be efficient for thick CFRP plates.

The study aims to explore the preparation of aviation mechanical carbon fiber reinforced plastics (CFRP) and the properties of CFRP composites. Taking the aero box body as an example, the mechanical properties of CFRP are studied. The preparation of CFRP is analyzed by searching the data. CFRP plates are explored according to the stress analysis of composite materials. The finite element analysis software ANSYS Workbench and UG software are adopted to build the 3D model of the aero box body. After adding materials in ANSYS Workbench and simplifying the UG model, the finite element analysis of the model is carried out by computer. The 3D model of the aero box is constructed, the finite element analysis of the aero box is carried out, and the mechanical properties of CFRP are explored. In this study, the possibility of the practical application of CFRP in the aviation box body lightweight is clarified, which gives a direction for the subsequent actual molding and guides the application of CFRP in aviation field.

Steel structure reinforced engineering makes extensive use of carbon fiber reinforced plastic (CFRP) plates. Although it happens frequently, the interfacial debonding of CFRP plate-reinforced steel beams has been the main cause of failure in flexural strengthened steel beams, which results in the brittle failure of steel structures. This paper proposes a novel percussion method to locate and quantify the debonding area based on the Welch power spectrum density (PSD) estimate, mel frequency cepstral coefficient (MFCC), and convolutional neural network (CNN). According to our knowledge, this is the first attempt to use the percussion method to identify and measure the debonding defects of steel beams strengthened by CFRP plates. Additionally, this experiment takes into account how percussion instruments affect localization and quantification. To begin with, the debonding location is qualitatively detected using the Welch PSD estimate method. The presented percussion method can successfully and accurately detect the interfacial debonding of CFRP plate-reinforced steel beams, according to repeated results. Subsequently, a novel CNN model is constructed to classify the various debonding areas based on the MFCC feature. In the end, the experimental findings show that the localization and quantification of the hammer types vary only slightly. Overall, the percussion-based approach can offer a fresh line of inquiry into the debonding problem on steel beams reinforced with CFRP plates.

To examine the microwave electromagnetic field (EMF) characteristics inside carbon fiber reinforced plastic (CFRP) structures, the quality factors (Q-factors) of reverberation chambers constructed of either CFRP or aluminum are evaluated and compared. In the CFRP structure, the four sidewalls and ceiling, which are originally made of aluminum, are replaced by CFRP panels, and then the uniformity of the field is evaluated. The standard deviation of the measured maximum electric field strength inside the chamber is less than 1.5 dB between 500 MHz and 6 GHz. The unloaded Q-factor of the CFRP chamber is almost identical to that of the all-aluminum structure below 2.5 GHz; however, it decreased by about 50 % between 2.5 GHz and 6 GHz compared to that of the all-aluminum structure. No significant difference is found in the loaded Q-factors of both structures.

Feasibility study of the rotary ultrasonic elliptical machining of carbon fiber reinforced plastics (CFRP)

In this study, timber column–sill joints strengthened with carbon fiber-reinforced plastic (CFRP) plates using bonds and screws were subjected to loading tests. Twelve joint specifications were considered depending on different combinations of the CFRP plate surface finish and thickness and the type of bond, and the corresponding effects on the load–displacement behavior of the joints were investigated. Three failure modes were observed in addition to the peeling of the CFRP plate. The specimens that failed owing to screw tear out and screw head pull-through in the CFRP plate or splitting of the sill showed load–displacement curves of a similar shape. Those that failed owing to buckling of the CFRP plate showed a rapid and substantial load decrease due to failure. This failure mode was only observed in 0.50 mm thick CFRP plate specimens. When a peel-ply CFRP plate was installed in the column–sill joint specimens, similar secant stiffnesses were observed in the silicon and epoxy resin-bonded specimens, both with high shear strength. Although the specimens with bonds with a high shear strength showed lower deformation performance, the specimens' maximum load increased with the bond's shear strength. The maximum load improved for a 0.75 mm thick peel-ply silicon- or epoxy-bonded CFRP plate. The load's maximum value after peeling the CFRP plate was 0.79–1.23 times as large as the maximum load of the no-bond specimens and did not change significantly.

Analysis of the in-plane fiber orientation distribution in carbon fiber composites using wide-angle X-ray diffraction

Adhesives can be used to form load-bearing joints in timber structures, both in repair and in new-build applications. An efficient and cost-effective method of making joints is to use rods or dowels or plate, bonded into pre-drilled holes in timber elements, by using structural adhesive for transferring structural loads between such elements. An adhesive is expected to hold materials together and transfer design loads from one adherend to other within a given service environment for the life of the structure. The behavior of the joints depends on many parameters such as glue-line thickness, types of rods, types of adherends etc. This paper reports the behavior of bonded-in joint by varying the plate types (steel and carbon fiber reinforced plastic (CFRP) plates) and timber types (Keruing and Kempas). To characterize the performance of the bonded-in joints, a series of test were conducted such as pull-out test and block shear test. As the strength properties of the joint greatly affected by the adhesive, the mechanical properties of the adhesives were also determined by conducting flexural and tensile test. The results show that the shear strength of bonded-in joint using CFRP plate is higher than bonded-in joint using steel plate.

Heat generation in CFRP (carbon fibre reinforced plastic) with electromagnetic induction can result in several benefits to manufacturing and production. However, during induction heating of anisotropic materials such as CFRP, the temperature distribution depends on electrical and thermal conductivity in different directions. This article presents a numerical model for computing the temperature distribution and heating power distribution in cross-ply CFRP plates, based on unidirectional plies, during induction heating. The unidirectional layers are represented as homogeneous and anisotropic domains in which electrical and thermal conductivity are represented with tensors. The electrical and thermal properties were measured and used in the numerical model to compute the temperature distribution in a number of CFRP-plates with different fibre volume fractions and layer thicknesses, and then the numerical model was validated by recording the temperature distribution with a thermographic camera during induction heating of the CFRP-plates. The experiments showed good agreement with the results from the numerical model.

The critical moment of unstrengthened and strengthened mono-symmetric and doubly symmetric steel beams was investigated using two approaches: analytical and finite element models (FEMs). The newly developed analytical model was formulated based on solving six homogeneous differential equations of a steel beam controlled by elastic lateral-torsional-buckling (LTB). The carbon-fiber-reinforced plastic (CFRP) plate was included in the analysis based on the virtual-section method. The solution consisted of a 6 × 6 eigenvalue problem. The proposed solution can predict reasonably the critical moment in the elastic range of a steel beam strengthened fully or partially at top or bottom flanges with CFRP plates. Twenty-six FEMs were built using ABAQUS software to examine the accuracy of the proposed analytical model. The FEM models included: unstrengthened and strengthened steel beams with 1-m and 2-m lengths of composite strips. Due to lack of experimental data in the elastic LTB stage and in order to further validate the analytical model, an extension of the model was proposed to compare results with other available experimental data in the inelastic-buckling zone for steel beams strengthened with steel or CFRP plates. The comparison showed that the finite element and analytical models, utilizing the virtual-section concept of CFRP plate, can reasonably predict the improvement in moment-capacity of beams in the elastic- and inelastic-buckling zones.

Binary dynamic stochastic search algorithm with support vector regression for feature selection in low-velocity impact localization problem

A smart composite material system which has three smart functions of sensor, actuator and processor has been developed intend to apply to structure of house for controlling ambient temperature and humidity, hands of robot for holding and feeling an object, and so on. A carbon fiber reinforced plastics (CFRP) is used as matrix in the smart composite. The size of the matrix is 120mm x 24mm x 0.45mm. The CFRP plate is combined two Ni-Ti shape memory alloy (SMA) wires with an elastic rubber to construct a composite material. The composite material has a characteristic of reversible response with respect to temperature. A photo-sensor and temperature sensor are embedded in the composite material. The composite material has a processor function to combine with a simple CPU (processor) unit. For demonstrating the capability of the composite material system, a model is built up for controlling certain behaviors such as gripping and releasing a spherical object. The amplitude of gripping force is (3.0 plus/minus 0.3) N in the measurement, which is consistent with our calculation of 2.7 N. Out of a variety of functions to be executed by the CPU, it is shown to exert calculation and decision making in regard to object selection, object holding, and ON-OFF control of action by external commands.

Multi-Functional Measurement Using a Single FBG Sensor

Simulations of carbon-fiber-reinforced plastics (CFRP) using the finite element method in electromagnetic tomography nondestructive evaluation systems are presented in this paper. Ansoft Maxwell 3D models describing the interaction of the sensors with both unidirectional and cross-woven plate samples are built and analyzed to show the CFRP orientations. A circular sensors array is designed and 400 test holes are punched through the CFRP plate respectively in order to acquire the sensitivity matrix data based on which the image of the plate can be reconstructed. Calculation shows that the proposed method can roughly sense the damaged area.

In this paper, a novel tool wear mechanism in low-frequency vibration–assisted drilling (LFVAD) of carbon fiber–reinforced plastic (CFRP)/Ti stacks and its individual layer has been proposed. Firstly, the difference of the effective rake angle, effective clearance angle, undeformed chip thickness, and tool-workpiece contact length between low-frequency vibration–assisted drilling and conventional drilling (CD) was analyzed based on the kinematic model. Then, the strength at different positions of the cutting edge was evaluated. Furthermore, the drilling experiments of CFRP/Ti stacks, CFRP plate, and Ti plate individually were taken under LFVAD and CD processes. Finally, the tool wear mechanism and the benefit of CFRP/Ti stacks and CFRP plate processed by LFVAD were expounded by kinematic analysis results, the analysis of drilling force, SEM images, and the profile of the cutting edge. The results show that the inner edge close to the chisel edge could be the weakest position of the drill in LFVAD. As the mean drilling force of LFVAD is lower than CD, the total wear volume of LFVAD is smaller than CD. Due to the change in the resultant cutting speed angle and the undeformed chip thickness, LFVAD produces the longer tool-workpiece contact length on the rake face and the flank face, which directly leads to a more uniform tool wear and a self-sharpening effect on the cutting edge. Thus, the reduction in the effective rake of the drill used in LFVAD is obviously smaller than the reduction in conventional drilling. The reduction in the effective clearance angle of the drill used in the LFVAD is also less than the reduction in conventional drilling, while this difference is attenuated as the cutting radius increases. The edge radius of the cutting edge is found to be much smaller than CD. In summary, the difference in the cutting edge geometry between LFVAD and CD is the root cause of the tool used in LFVAD to avoid severe edge chipping.