As an alternative evaluation method to the four-point bending test, a strength evaluation and prediction method for carbon-fiber-reinforced polymer (CFRP)/Nomex honeycomb sandwich panels for aircraft interiors was investigated using edgewise compression tests. The failure mode of the edgewise compression test was experimentally demonstrated to be identical to that of the four-point bending test, that is, the delamination between the face sheet (CFRP) and core originated from face sheet local buckling. The same origin of failure was confirmed by buckling eigenvalue analysis. Furthermore, it was demonstrated that the calculation accuracy of buckling load analysis can be improved by using postbuckling analysis, which considers the initial irregularity. The computation time for buckling eigenvalue analysis by edgewise compression can be reduced to 1/100 of that required for bending analysis. Therefore, it is expected to reduce the development cost for optimizing the material configuration of sandwich panels using edgewise compression analysis.

Carbon fiber reinforced plastics (CFRPs) have been widely used in weight-critical applications such as aircrafts owing to their lightweight and excellent mechanical properties. However, a few challenges such as poor delamination toughness of CFRP laminates have impeded the wide-scale commercial application of CFRP composites. To address these issues, we conducted a feasibility study of recycled carbon fiber (CF). In this study, CFRP composites were interleaved with non-woven CF tissues (NWCTs) to improve the interlaminar fracture toughness. The results indicated that the Mode-1 fracture toughness of the composite increased remarkably upon NWCT interleaving. The initial and propagation fracture toughness increased about 6.7 times from 171 to 1148 J/m² and 4.4 times from 372 to 1644 J/m², respectively, after NWCT interleaving. A dropweight impact test and tensile test were also conducted.

Piercing is an essential process for composite structures because they are usually near-net-shape manufactured to reduce further machining operations. Although drilling is commonly used to increase productivity, punching by out-of-plane shear loading is also used. This study analyzes the open-hole compressive (OHC) strength and fracture morphologies of carbon fiber reinforced plastic (CFRP) laminates with punch-and drill-pierced holes (CFRP-PPH and CFRP-DPH, respectively).The damage in CFRP-PPH and CFRP-DPH was evaluated using the delamination factor. The OHC failure process was experimentally assessed by in-situ observation during the OHC test. The results showed that the OHC strength of CFRP-PPH and CFRP-DPH was not correlated with the delamination factor. It was observed that micro-buckling was initiated in the middle layer of CFRP-PPH owing to the roughness of the characteristic machining surface induced during punching. In contrast, for CFRP-DPH, micro-buckling was initiated in the upper layer because of the tear and matrix cracks generated during drilling.

A method for estimating the elastic properties of random oriented chopped UD tape reinforced thermoplastic composites (CTT) containing different UD tape lengths from in-plane strain distributions obtained in tensile tests was investigated using 3D-DIC analysis. The probability density function (PDF) and autocorrelation function of the in-plane strain distribution of 100 MPa were obtained. The elastic modulus was measured from nominal stress-strain data. The difference of the mean value of the theoretically calculated elastic modulus from the gauge length made dimensionless by the autocorrelation length indicates that the PDF of the in-plane strain distribution is correlated with the elastic modulus properties. The probabilistic properties of the elastic modulus distribution obtained at each point on the specimens were examined, revealing that the obtained result depended not only on the size of the measurement section but also on the data processing method. The elastic modulus of CTT must be defined as a constant value at the limit of the gauge length and the number of samples, and it was shown that it is appropriate to define it as the reciprocal of the stochastic convergence value of elastic compliance for general specimens with small width.