Nobuhide Uda

Strain analysis for moiré interferometry using the two-dimensional continuous wavelet transform

In this paper, we introduce the two-dimensional continuous wavelet transform for the automated strain analysis of the moiré interference fringe pattern. The Fourier transform method has been widely used for automated analysis of an optical interference fringe pattern. However, this method is hardly applicable to the analysis of the fringe pattern, which includes large displacement range or discontinuities. We show the advantages of the wavelet transform method by applying it to experimental results on composite laminates.

Impact damage and residual tensile strength of a CF-SMC composite

In this study, the impact damage and the tension after impact (TAI) strength of a carbon-fiber-reinforced sheet molding compound (CF-SMC) are analyzed. First, low-velocity impact damage is introduced to several CF-SMC coupon specimens for a variety of impact energies. Next, the impact damage is observed by ultrasonic inspection and optical microscopy to determine the damage state and quantify the damage area and depth. Then, the TAI strength is measured and correlated with such parameters as maximum impact load, impact energy, and damage area and depth. Finally, a simple fracture-mechanics model for predicting the TAI strength is proposed. It is proved that the TAI strength depends on the impact damage depth.

Compressive failure analysis of quasi-isotropic composite laminates fabricated with quasi-unidirectional woven fabric

The effect of configuration of quasi-unidirectional woven fabric on the compressive failure modes of quasi-isotropic composite laminates was investigated in this study. Two kinds of out-of-plane fiber waviness were formed in the composite laminates due to different quasi-unidirectional woven fabrics and measured using a fast Fourier transform method. The compressive failure modes of the composite laminates were identified using experimental and numerical methods. It was found that the compressive strength of a composite laminate fabricated using long-pitch weft fabrics was greater than that fabricated using standard-pitch weft fabrics. The relationship between the compressive strength and the configuration of quasi-unidirectional woven fabrics was investigated in a parametrical study, and four compressive failure modes were found: the axial compressive, normal, bending, and shear failure modes.

Observation of the secondary failure near the tip of transverse cracks in a GFRP cross-ply laminate

Concerning the nonlinear behavior of a glass/epoxy cross-ply laminate under tension, an experiment was performed to verify our previous predictions that some secondary failure will be produced near the tip of transverse cracks and the failure will prevail at relatively high load. Results were satisfactory. The secondary failure is a tree- shaped cracking. Based on the results, a new failure mechanism is proposed.

Effect of micro in-plane fiber waviness on compressive properties of unidirectional fabric composites

In this paper, a combination of experimentation and analysis is used to study the effect of micro in-plane fiber waviness on the compressive properties of unidirectional fabric composites. The experimental part includes a measurement of the micro in-plane fiber waviness in two types of unidirectional fabrics, manufacturing composites with each unidirectional fabric via VaRTM process and tests for establishing the compressive modulus and strengths of the composites. The compressive strengths were confirmed to be affected by the micro in-plane fiber waviness, but the compressive modulus was not. Furthermore, a two-dimensional numerical model is proposed to explain our experimental results. The numerical results indicate that the tensile stress (owing to the micro in-plane fiber waviness) and compressive stress along the weft and warp directions, respectively, of the composite lead to reductions in the compressive strength.

Vacuum infusion method for woven carbon/Kevlar reinforced hybrid composite

The vacuum assisted resin transfer moulding (VaRTM) or Vacuum Infusion (VI) is one of the fabrication methods used for composite materials. Compared to other methods, this process costs lower than using prepregs because it does not need to use the autoclave to cure. Moreover, composites fabricated using this VI method exhibit superior mechanical properties than those made through hand layup process. In this study, the VI method is used in fabricating woven carbon/Kevlar fibre cloth with epoxy matrix. This paper reports the detailed methods on fabricating the hybrid composite using VI process and several precautions that need to be taken to avoid any damage to the properties of the composite material. The result highlights that the successfully fabricated composite has approximately 60% of fibres weight fraction. Since the composites produced by the VI process have a higher fibre percentage, this process should be considered for composites used in applications that are susceptible to the conditions where the fibres need to be the dominant element such as in tension loading.