Solid Composite Laminate Research Articles

Light-Weight Design of CRH Wind Deflector Panels based on Woven Textile Sandwich Composites

The woven textile sandwich composite (WTSC) is a promising lightweight composite. In bending, two competing core shearing failure modes reduce the strength; deflection induced by the core shearing deformation reduces the flexural rigidity. To replace a solid composite laminate, the span of WTSC panel must be greater than a critical value, which was deduced on the condition that the load capacity and flexural rigidity of the WTSC panel are equal to those of the composite laminate. Three WTSC panels were tested in bending, so that the failure modes were observed, and the critical spans were determined. Using the alternative design method, the WTSC based wind deflector with reduced weight has been fabricated and mounted on the CRH (China Railway High-speed).

Ultra-light CRH wind deflector fabricated by woven lattice sandwich composites

An alternative design method was suggested to design an ultra-light hierarchical wind deflector fabricated by woven lattice sandwich composites (WLSCs). The alternative method is based on the criterion that the alternative sandwich structure should have equal bending strength and bending rigidity to the replaced solid composite laminate. Two alternative structures for wind deflectors were suggested and analyzed based on corresponding structural models. Stress and strain predictions were well consistent with the experiments, which reveal that adopting hierarchical WLSC structure, the new designed wind deflector has greater load capacity, and meanwhile the weight is reduced at a level of more than 50%.

Compression After Impact and Fatigue of Reconsolidated Fiber-reinforced Thermoplastic Matrix Solid Composite Laminate

Carbon fiber-reinforced poly-phenylene sulfide laminate coupons were impacted at low-energy in a drop-tower machine and subsequently fatigued in a four-point bending fixture. The doubly damaged test pieces were then hot-press reconsolidated and inspected nondestructively by vibrothermography to check their structural integrity. The residual mechanical properties of the laminate in both the as-damaged and as-repaired conditions were determined by compression loading with the in-plane strain fields determined via a digital image correlation system. Cross-section views of damaged and repaired samples were analyzed by light optical microscopy and correlated to residual mechanical properties, as were the digital image correlation and nondestructive test results. Based on the values of stiffness and ultimate strength of the repaired laminates, 10J was inferred as the maximum impact energy at which it is worthwhile performing hot-press reconsolidation, in view of the applied fatigue history following impact.

Terahertz spectroscopy approach of the fiber orientation influence on CFRP composite solid laminates

Terahertz ray (T-ray) imaging applications have provided one of the most promising new powerful nondestructive evaluation techniques, and new application systems are under process development for area applications. Detecting flaws and defects in fiber reinforced plastic (FRP) composite laminates due to flaws in FRP composite laminate that affect laminate properties, including stiffness, strength, and thermal behavior, is very important. In this study, a new time-domain spectroscopy system was utilized for detecting and evaluating the flaws in FRP solid composite laminates. Extensive experimental measurements in reflection mode were made to map out T-ray images. In particular, electromagnetic properties, such as refractive index, were estimated in this characterization procedure. The estimates of properties were in good agreement with known data. Using these characteristic material properties, we successfully demonstrated the characteristics of the T-ray behavior propagating through FRP composites. Furthermore, layup effect and flaws of FRP composite laminates were observed in reflection mode, and limitations were discussed in the T-ray processing.

ONE-SIDED ULTRASONIC CHARACTERIZATION OF CFRP COMPOSITE LAMINATES

Ultrasonic NDE of composite laminates is usually analyzed on the backwall echoes of the specimen. In the inspection of actual composite structures, the back surface of the part was curved or contained complex geometry and did not provide a usable backwall echo. In this work, a one-sided pitch-catch setup was used in the detection and evaluation of flaws and material anomalies in solid composite laminates. Two miniature potted Rayleigh wave transducers (for generating surface waves in contact mode on steel) were joined head-to-head and used in the pitch-catch mode on the surface of composites. The pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to fiber orientation of the CFRP composites, including low level porosity, ply waviness, and cracks.

Thermally Induced Loads of Fastened Hybrid Composite/Aluminum Structures

Large composite structures have been increasingly used in the aviation industry. New applications of composite materials include primary structures such as aircraft fuselages. These large composite parts are sometimes attached, either by the fasteners or adhesive bonding, to metallic structures. Because of the large coefficient of thermal expansion mismatch between the metallic and composite structures, the temperature change from the aircraft assembly line to the actual flight condition induces high thermal stresses during flight in both the composite fuselage and aluminum frames. An experimental program was executed to determine the interaction between the fastened Z-shaped aluminum beams and the solid composite laminate. An analytical model was also developed to simulate the thermal/mechanical behavior of the hybrid composite/metal structure. Finite element analysis was conducted to determine the parameters necessary for the analytical model. The results from the developed analytical model were found to correlate well with experimental results.

Effect of Anisotropic Characteristics of Composite Skins on the Electromagnetic Wave Propagation in the Foam Core Sandwich Structures

The propagation of electromagnetic waves in the foam core sandwich structures is highly affected by anisotropic permittivity and loss tangent of composite skins. Even though many investigations were focused on the propagation of electromagnetic waves in the composite materials in last several decades, little investigations were carried out to understand adequately the propagation of the electromagnetic waves in the foam core sandwich structures. In this study, the transmittance of the arbitrary linearly polarized incident TEM waves through the solid composite laminate with various stacking sequences and foam core sandwich structures with composite skins was calculated as functions of fiber orientation of composites and incident angle of the wave by the analytical model.

The properties of wet‐formed thermoplastic sheet composites

AbstractGlass fiber reinforced thermoplastic matrix sheet composites of polypropylene and poly(ethylene terephalate) were produced in a two‐stage pilot scale impregnation and consolidation process. The first stage consisted of preparing wet‐formed mats of long, discontinuous fibers and polymer powder on an inclined wire paper‐making machine. The second stage consisted of consolidating approximately 15 wet‐formed mats into a solid composite laminate by the application of heat and pressure in a compression press. The resulting composites had a nominal glass content of 26 wt% (∼12 vol %). Flexural strengths as high as 108 MPa for polyproplene composites and 132 MPa for poly(ethylene terephthalate) composites were measured on specimens cut from stamped parts. The flexural modulus of the polypropylene compsites reached 5.4 Gpa, while the modulus of the stiffest poly(ethylene terephthalate) composite was 8.1 Gpa. The impact properties of the composites were equally good. Polyproplene compsites absorbed up to 62 J/cm during an instrumented falling dart impact test, while poly(ethylene terephthalate) composites absorbed as much as 32 J/cm during the same test.