Thin Carbon Fiber Reinforced Plastic Research Articles

Ballistic performance of thin CFRP laminates under complex in-plane preload

In this research, we explore the effects of complex in-plane quasi-static loads on the high-velocity impact response of Carbon Fiber Reinforced Plastic (CFRP) composite laminates, grounded in the practical context of various working loads combined with potential high-velocity impacts experienced by aircraft. The specific complex in-plane loads studied include uniaxial tension and compression, biaxial tension and compression, and a combination of tension and compression preloading. The results show that the complexity of in-plane preloads, along with pre-compression, reduces the ballistic limit velocity. Biaxial preloading, especially in compression, greatly compromises the specimen's ballistic resistance. The study also proposes a theoretical model based on energy conservation principles to predict the ballistic limit velocity of CFRP laminates under various preloading conditions. The research provides valuable insights for designing composite structures and highlights the importance of considering in-plane preloads in assessing thin CFRP ability to withstand ballistic impacts.

Laser microdrilling of CFRP with a nanosecond-pulsed high-power laser

The global demand for air travel and air transport is expected to further increase in the next couple of years, and so the environmental protection will also increasingly come into focus again. In the aviation sector, this means not only saving fuel and reducing emissions but also reducing the noise pollution caused by aircrafts. For this purpose, sound-absorbing acoustic liners are used, which consist of a sandwich structure with one perforated skin layer. To reduce weight, these outer layers are often made of carbon fiber-reinforced plastic (CFRP). For manufacturing these CFRP skin layers, laser drilling offers specific benefits, but when it comes to industrial applications, further process improvements are necessary. Although laser microdrilling is a well-known process in laser materials’ processing, it has not yet been sufficiently investigated for the processing of carbon fiber-reinforced plastics. This study investigates the quality and efficiency of laser microdrilling with a 1.5 kW nanosecond-pulsed high-power laser for percussion drilling and helical drilling of thin CFRP laminates. The efficiency was evaluated in terms of drilling depth, the amount of energy required to remove a specific volume of material, and the time required to remove a specific volume of the material. The quality evaluation focused on the heat-affected zone and the hole taper. The efficiency and quality results were set in relation to higher-level parameters such as energy fluence in the laser spot, pulse overlap, or total energy applied. This facilitates future transferability to similar laser processes that may use laser machines and system technology with deviating specifications.

On the Directivity of Lamb Waves Generated by Wedge PZT Actuator in Thin CFRP Panel.

This paper addresses investigation of guided-wave excitation by angle-beam wedge piezoelectric (PZT) transducers in multilayered composite plate structure with orthotropic symmetry of the material. The aim of the present study is to determine the capability of such actuators to provide the controlled generation of an acoustic wave of a desirable type with the necessary wavelength, propagation distance and directivity. The studied CFRP (Carbon Fiber Reinforced Plastic) panel is considered to be homogenous, with effective elastic moduli and anisotropic structural damping, whose parameters were determined experimentally. According to the results of dispersion analysis and taking into account the data of wave attenuation in a highly damping CFRP composite, the two types of propagating waves A0 and S0 were considered theoretically and experimentally in the frequency range of 10–100 kHz. Using the results of a previous study, we reconstructed the structure of the wedge actuator, to develop its finite-element (FE) model, and a modal analysis was carried out that revealed the most intense natural vibration modes and their eigenfrequencies within the frequency range used. Both experimental and numerical studies of the generation, propagation, directivity and attenuation of waves in the orthotropic composite panel under study revealed the influence of the angular orientation of the actuator on the formation of wave patterns and allowed to determine the capabilities of the wave’s directivity control.

Simple electric-voltage-change-analysis method for delamination of thin CFRP laminates using anisotropic electric potential function

Although the electrical-resistance-change method is useful for monitoring delamination cracking of carbon-fiber-reinforced plastic (CFRP) laminates, the method requires many experiments or FEM analyses to obtain the relationship between the electrical resistance changes and parameters describing delamination cracking. In our previous studies, one of the authors proposed using an anisotropic electric potential function to analyze electric current density in CFRP laminates. The function was applied only to thick CFRP laminates. In the present study, the method is expanded to thin CFRP laminates using an image method. The number of images is determined using the electric current analysis of thick CFRP laminates. The electric potential changes caused by delamination cracking can be calculated using an anisotropic doublet line. The associated method is applied to calculate the electric voltage change at the surface of a thin CFRP laminate. The results are compared with an FEM analysis, and, overall, the method is shown to be very effective.

Optimization of machining parameters at high speed drilling of carbon fiber reinforced plastic (CFRP) laminates

High speed machining is now acknowledged to be one of the key manufacturing technologies to ensure high productivity and throughput. Drilling of CFRP, though a challenging task, is being performed successfully at low spindle speeds. However high speed drilling in CFRP thin laminates has not been explored much. This paper reports an experimental investigation of a full factorial design performed on thin CFRP laminates using K20 carbide drill by varying the drilling parameters such as spindle speed and feed rate to determine optimum cutting conditions. The hole quality parameters analyzed include hole diameter, circularity, peel-up delamination and push-out delamination. Analysis of variance (ANOVA) was carried out for hole quality parameters and their contribution rates were determined. Genetic Algorithm (GA) methodology was used in the multiple objective optimization (using MATLAB R2010a software) to find the optimum cutting conditions for defect free drilling. Tool life of the K20 carbide drill was predicted at optimized cutting speed and feed.

Electric Current Analysis for Thick Laminated CFRP Composites

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.

CFRPの導電率の積層理論

The present paper deals with a new lamination theory to calculate electric current between two probes on Carbon Fiber Reinforced Plastic (CFRP) laminates. 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. The electric current concentrates near the surface where the electric current is applied for thick CFRP laminates. 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. For the non-thick and non-thin (middle thickness) CFRP plate, an approximation method is proposed here. 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. Cross-sectional 2-D FEM analysis is used to obtain the contribution function for non-thick CFRP plates. 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.

Effect of Dent on Self-Sensing Method of CFRP

Authors’ group has been done researches on the damage monitoring of the laminated Carbon Fiber Reinforced Plastic (CFRP) using the electrical resistance change method. The method adopts reinforcement carbon fibers as sensors, and it is called self-sensing method. Using thin CFRP laminates, delamination crack location and dimension are identified with the electrical resistance change method. However, the electrical resistance decreases when a delamination crack is made in a thick CFRP beam. The present paper experimentally investigates the effect of the dent for the measurements of electrical resistance change. Indentation tests are performed for the thick CFRP plates. The effect of the dent is calculated compared with the effect of piezoresistivity caused by the residual stress relief. As a result, the effect of the dent is larger than the effect of the residual stress relief for the thick CFRP. For the thick CFRP, dents cause the significant reduction of the electrical resistance in the thickness direction, and that causes electrical resistance decrease.

A Comparison of the Vibration Characteristics of Carbon Fiber Reinforced Plastic Plates with those of Magnesium Plates

An experimental and numerical investigation is conducted to evaluate vibration characteristics of an advanced composite material system, namely carbon fiber reinforced plastic (CFRP), relative to a magnesium alloy currently used in the vibration testing industry. Experimental test specimens for both materials, with varying thicknesses, are tested with two boundary conditions — the free condition, to evaluate the natural frequencies and damping of the two materials and, secondly, a general constrained condition, typical of vibration testing. Experimental modal analysis techniques are used to measure the vibration characteristics including natural frequencies, damping and mode shapes. The results from these tests show that the natural frequency and mode shape for relatively thin CFRP plates were comparable with those of magnesium plate. Although the mode shapes also compare well for thick CFRP and magnesium specimens, the natural frequencies were found to have significant differences between the two material systems. The largest difference between the two material systems, present for all thicknesses, is found to be the damping values for the respective vibration modes. This unique characteristic of the CFRP material presents an opportunity for a performance increase in the vibration testing system’s community.

D08 CFRPのヘリカル加工における穴あけに関する研究 : 各種エンドミルによる加工精度への影響(OS-14 先端材料・難削材の加工(2))

CFRP (Carbon Fiber Reinforced Plastic) has higher specific strength, modulus of elasticity and so on. CFRP is, however, well known as difficult-to-cut material which has very strong physical and mechanical characteristics. Drilling technique of CFRP which is one of the most important cutting operations is currently carried out in industrial factories. In this research, we tried to make high accuracy drilling process by helical movement method of cutting tools on the CFRP plates. Cemented-carbide ball-nose end mill is suitable to drill out thin CFRP plates which dimension of L/D (Length per Diameter) is below 0.3. On the other hand, it is not easy to make drill holes on the thick CFRP plate by ball-nose and square end mill because of inefficient evacuation for cutting chips.

Development of a Light Weight Prosthetic Frame Made of CFRP. (A Joint Structure Comprising of a CFRP Frame and a Metal Knee Joint).

Using FEM structural analysis, a load bearing frame for a light weight prosthesis made of carbon fiber reinforced plastic (CFRP) was developed, complying with both severe spatial restrictions and the ISO specification for strength. This paper focuses on the optimum design of the joint between the thin CFRP frame and a metal knee joint. A special bracket, which is implanted into the frame and prevents rotation of the knee, was developed for the joint, in order to reduce the stress concentration generated around the bracket hole of the frame. The orientation of the carbon fiber cloth ply was optimized taking the anisotropy of the CFRP into account. The static fracture strength of the CFRP frame predicted by the analyses agreed well with the results of fracture tests.