Characterizing the deformation of woven textile composites

7 August 2017
Kadir Bilisik
The compression-after-low-velocity-impact properties of samples is improved by multistitching techniques and the addition of nanoparticles.

Strong and lightweight textile composites are commonly used in structural parts for aerospace applications. In addition, a variety of stitching techniques (hand or machine) can be used to reinforce the through-the-thickness reinforcement of the textile preforms. Indeed, in general, such stitched woven composites exhibit high damage-tolerance properties. Nonetheless, results from some compression-after-impact (CAI) tests1 on such textiles suggest that the CAI load can cause buckling deformation and reduced composite performance.2

The effect of stitching on woven composites has therefore been investigated in several recent studies. For example, it has been reported that buckling in the delaminated area can lead to unstable damage propagation.3 It has also been found that adding nanosilica to carbon-fiber-reinforced composites increases the CAI strength of the material.4 This strength improvement arises because of the enhanced stiffness and impact resistance of the composites, i.e., imparted via the incorporation of the silica-based nano/micromaterials.

In earlier work, we showed that the damage performance of multistitched composites can be improved through the addition of nanoparticles.5 In this study we have thus continued our investigations by examining the compression-after-low-velocity-impact (CALVI) properties of multistitched nanocomposites.6 In particular, we have tested multistitched preforms that contain plain-weave E-glass (fiber glass) woven fabrics, as well as nano- and microparticles (30–40nm and 1.5–6.7μm in size, respectively). The stitching fiber we used was a para-aramid material (Kevlar 129). In total, we produced seven E-glass preforms for our experiments (as listed in Table 1). For the multistitched preforms, we (hand or machine) stitched the fabric layers along the 0° (warp), 90° (filling), and ±45° (diagonal) directions, as illustrated in Figure 1, and we used a [0°/90°]4 stacking sequence.

List of the seven tested E-glass preforms, showing the type of stitching and the reinforcing nanoparticles or microparticles they contain.

SampleStitching typeNanoparticles (5%)Microparticles (5%)
T1aUnstitched
T2bUnstitchedsilica
T3bUnstitchedcalcium silicate
T4aMultistitched (machine)
T4bMultistitched (hand)
T5aMultistitched (machine)silica
T5bMultistitched (hand)silica

Schematic diagrams of the (a) machine and (b) hand stitching patterns (i.e., along the 0, ±45, and 90° directions) used in the E-glass preforms.

We used a vacuum-assisted resin transfer molding process to fabricate our composite specimens. Specifically, we used a high-performance polyester resin (Crystic 703PA) and a mechanical stirrer to mix this resin with the nano/microparticles. We then performed—with the use of a drop-weight instrument (CEAST Fractovis Plus)—a low-velocity impact test, following a standard methodology,7 and subsequently conducted the CALVI measurements on the impacted multistitched composites (with the use of a Shimadzu AG-XD 50 tensile instrument, following a standard procedure8).

The results of our CALVI tests—see Figure 2(a)—show that the CALVI strength of the T5a sample (i.e., machine stitched, with nanosilica) was higher than the rest of the specimens. We also observe a similar trend in the specific CALVI strength results. In addition, we find—see Figure 2(b)—that all our multistitched (T4a and T4b) and multistitched/nanoparticle structures (T5a and T5b) had large damaged areas on both their front and back surfaces. These samples also exhibited greater CALVI strengths (maximum loads) than all the unstitched composites (i.e., T1a, T2b, and T3b). These results thus indicate that the multistitching approach, and the addition of the nanoparticles, enhances the CALVI properties of our composites.


(a) Compression-after-low-velocity-impact (CALVI) and specific CALVI (SCALVI) results for the seven composite structures (as listed in Table 1). (b) Measured size of the damaged areas on the front and back surfaces of the samples after the CALVI tests. The maximum (max) CALVI load for each sample is also shown.6

In our work we also examined the damage zone of our T5a structure in further detail. For instance, we show optical microscope and scanning electron microscope (SEM) images of this sample in Figure 3. From the optical microscope image—see Figure 3(a)—we see that the zone contains regions of local fiber–matrix debonding, parallel matrix cracking, and minor fiber breakage. The SEM images of the sample—see Figure 3(b) and (c)—also reveal the occurrence of kinking (e.g., local minor layer debonding) and severe fiber breakage. In addition, we observe that the nanosilica distribution within this sample was somewhat homogeneous, but that there were also local agglomerations (e.g., in the local damaged zone). This uneven distribution was probably caused partly by uneven fiber placement during stitching and partly by the specific nanosilica mixing conditions.


(a) Optical microscope image (×6.7 magnification) of failure characteristics on the front surface of the T5a sample. Scanning electron microscope images of the same sample illustrate the (b) warp-direction cross-sectional failure (scale bar indicates 10μm) and (c) the front surface failure (scale bar indicates 100μm).6

In summary, we have investigated the CALVI properties of multistitched (hand or machine) textile composites that are reinforced with either nanoparticles or microparticles of silica or calcium silicate. Our results indicate that the type of stitching, as well as the nano/microparticle size, affects the CALVI properties of the samples. Moreover, we find that the stitching confined the layer-to-layer delamination of the samples to the out-of-plane direction, and the fiber (yarn or tow)-to-fiber delamination to the in-plane direction. The outcomes of our experiments thus demonstrate that multistitching and nanoparticle addition can be used to enhance the CALVI performance, suppress delamination, and prevent severe failure of textile composites. In our ongoing work we are studying additional ways to enhance the stitching process (e.g., by using the high degree of freedom of a robotic stitching arm for nanostitching yarn). In this way we hope to reduce the amount of degradation during multistitching and improve the homogenization of nanoparticles within the resin/filament media. In addition, we are developing ‘nanoprepreg’ and nanostitching-based multistitched nanocomposites that can be used specifically as materials in aerospace and automotive applications.


Author

Kadir Bilisik
Department of Textile Engineering, Erciyes University

Kadir Bilisik is a full-time professor in the Faculty of Engineering. He specializes in the fields of fiber materials, 3D fabric structures, rigid and soft ballistics, nanomaterials, characterization, testing, and modeling of fabric structures.


References

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  2. T. Ishikawa, S. Sugimoto, M. Matsushima and Y. Hayashi, Some experimental findings in compression-after-impact (CAI) tests of CF/PEEK (APC-2) and conventional CF/epoxy flat plates, Compos. Sci. Technol. 55, pp. 349-363, 1995.

  3. H. Yan, C. Oskay, A. Krishnan and L. R. Xu, Compression-after-impact response of woven fiber-reinforced composites, Compos. Sci. Technol. 70, pp. 2128-2136, 2010.

  4. B. Nikfar and J. Njuguna, Compression-after-impact (CAI) performance of epoxy-carbon fibre-reinforced nanocomposites using nanosilica and rubber particle enhancement, 2nd Int'l Conf. Struct. Nano Compos. 64, pp. 012009, 2014.

  5. K. Bilisik and G. Yolacan, Low-velocity impact characterization of multistitched woven E-glass/polyester nano/micro composites, Textile Res. J. 84, pp. 1411-1427, 2014.

  6. K. Bilisik, Characterization of multi-stitched woven nano composites under compression after low velocity impact (CALVI) load, Polym. Compos., 2017.

  7. Standard test method for measuring the damage resistance of a fiber-reinforced polymer matrix composite to a drop-weight impact event ASTM D7136, 2015.

  8. Standard test method for compressive residual strength properties of damaged polymer matrix composite plates ASTM D7137, 2012.

DOI:  10.2417/spepro.006951