Lay-up Direction Research Articles

Analyzing the impact of veneer layup direction and heat treatment on plywood strain distribution during bending load by digital image correlation (DIC) technique

In this study, radiata pine veneers and phenol-formaldehyde resin were used to prepare specimens of 5-ply plywood with different layup directions and heat treatments of veneers. The physical and flexural properties of the plywood specimens were assessed, and digital image correlation (DIC) analysis was employed to determine the strain distribution of the plywood under bending loads. The results of the static mechanical strength and DIC tests showed that the plywood with a small-angle veneer layup ([0]5 and [0,22.5,0,22.5,0]) exhibited a better longitudinal modulus of rupture (MOR//), while [0,45,0,45,0] plywood showed the least bending strength and most strain. Moreover, the results revealed that for plywood composed of veneers that were fully heat treated at 200 °C (5T200), the moisture content was efficiently decreased, and the modulus of elasticity parallel to grain (MOE//) was the highest. The DIC images indicated that the largest strain along the x-direction (εxx) was concentrated on the tensile side of untreated plywood (5N) and on the opposite side of plywood composed of heat-treated veneers, except for the plywood composed of veneers treated at 220 °C (5T220). Of these, 5T200 plywood showed the least strain. In addition, the plywood with 200 °C heat-treated veneers instead of face and core layers (NTNTN200) or crossband layers of untreated veneers (TNTNT200) had larger strain values than 5N and 5T200 plywood specimens, with NTNTN200 plywood having the greatest strain. According to the above results, appropriate layering and heat treatment of veneers can effectively improve the dimensional stability and flexural properties of plywood.

Kink band orientation of 3D printed continuous carbon fiber composites under compressive loading

For continuous carbon fiber-reinforced plastic (cCFRP), in the case of loading in the longitudinal direction, occurrence of kink band failure causes compression strength to be lower than the tensile strength. Furthermore, 3D-printed cCFRP may exhibit intrinsic compressive behavior depending on the printing orientation. In this study, two types of rectangular specimens were fabricated using the Markforged Mark Two > 3D printer. The first was the in-plane specimen, whose width direction was parallel to the print bed and thickness direction was along the layup direction. The second was the out-of-plane specimen, whose width direction was the layup direction and thickness direction was parallel to the print bed. Compression tests were performed, and the experimental results were compared. As a result, the compressive strengths of both types were similar, and the kink bands always grew in the lay-up direction. For the out-of-plane specimens, nonlinear stress–strain curves were observed. This may be due to the delamination crack growth caused by the low strength in the lay-up direction and the existence of initial defects. This study experimentally investigated the effect of two different printing orientations of 3D printed cCFRP to its strength and failure mode, and this work shows the importance of considering structural deformation due to compression loading in 3D printed cCFRP.

Improving the Mechanical Properties of CCFRPLA by Enhancing the Interface Binding Energy and Strengthening the Anti-Separation Ability of a PLA Matrix.

Additive manufacturing (AM) can produce almost any product shape through layered stacking. The usability of continuous fiber-reinforced polymers (CFRP) fabricated by AM, however, is restricted owing to the limitations of no reinforcing fibers in the lay-up direction and weak interface bonding between the fibers and matrix. This study presents molecular dynamics in conjunction with experiments to explore how ultrasonic vibration enhances the performance of continuous carbon fiber-reinforced polylactic acid (CCFRPLA). Ultrasonic vibration improves the mobility of PLA matrix molecular chains by causing alternative fractures of chains, promoting crosslinking infiltration among polymer chains, and facilitating interactions between carbon fibers and the matrix. The increase in entanglement density and conformational changes enhanced the density of the PLA matrix and strengthened its anti-separation ability. In addition, ultrasonic vibration shortens the distance between the molecules of the fiber and matrix, improving the van der Waals force and thus promoting the interface binding energy between them, which ultimately achieves an overall improvement in the performance of CCFRPLA. The bending strength and interlaminar shear strength of the specimen treated with 20 W ultrasonic vibration reached 111.5 MPa and 10.16 MPa, respectively, 33.11% and 21.5% higher than those of the untreated specimen, consistent with the molecular dynamics simulations, and confirmed the effectiveness of ultrasonic vibration in improving the flexural and interlaminar properties of the CCFRPLA.

Energy dissipation theory performance of different layup patterns CFRP/aluminium alloy hat-shaped hybrid beams under three-point bending conditions

This study investigates the bending failure behaviour of CFRP-reinforced aluminium alloy hat-shaped hybrid beams under three-point bending conditions. Firstly, three-point-bending experiments are conducted for four kinds of hybrid beams with different layup directions of CFRP. It is found that the layup direction has a more significant impact on the maximum loads. The load carrying capacity of the hybrid beam tends to stabilise around a certain load after decreasing from the maximum value of load. Subsequently, FE models of hybrid beams with inner, external and concurrent reinforced patterns are established to analysis the effect of locations of reinforced structure on the bending characteristics. It is found that the effect of reinforced structure location is influenced by the relative relationship between the thicknesses of aluminium alloy and the CFRP parts. Finally, a theoretical model of hybrid beams under three-point bending condition is proposed to predict the bending characteristics.

Mechanical behavior of 2D woven SiCf/SiC composites investigated by acoustic emission and digital image correlation

In this study, the mechanical properties of two-dimensional (2D) woven SiCf/SiC composites that were fabricated via precursor infiltration and pyrolysis (PIP) were evaluated through a three-point bending test, and the failure processes of the composites were monitored under different loading directions by acoustic emission (AE) system and digital image correlation (DIC) technique. Multiple characterization methods conducted on the 2D woven SiCf/SiC composites to examine the failure behaviors indicated that the damage process was dominated by compressive stress in the composites which loading direction was parallel to the layup direction, and the damage occurred continuously during the test. In contrast, the composites were primarily subjected to tensile stress when loading was perpendicular to the layup direction. The mutually supporting results obtained by AE system and DIC technique demonstrate that the combination of multiple analytical methods provides a compelling approach to assess the mechanical behavior of SiCf/SiC composites.

Effect of build-up orientations and process parameters on the tensile strength of 3D printed short carbon fiber/PA-6 composites

3D printers using fused filament fabrication (FFF) with thermoplastic filaments have been employed for rapid prototyping applications. The present research focuses on 3D-printed short carbon fiber/PA-6 composites. Specimens with four types of build-up orientations (0°, 90°, ±45°, and layup) were fabricated using two types of 3D printer: Mark Two, produced by Markforged, and X-Plus produced by Qidi Tech. Tensile tests were performed on these specimens. X-ray CT and SEM observations were conducted to investigate the defects and gaps between the print paths. The effect of the bed temperature and extrusion rate were experimentally investigated. For the ±45° specimens fabricated using Mark Two, a large gap between the print paths was confirmed. An increase in the extrusion rate of 5% (1.05) and a minor increase in the nozzle temperature of 3.6% (from 275 °C to 285 °C) yielded a smaller gap between the print paths, 20 % higher tensile strength of the ±45° specimen, 10 % higher tensile strength of the 0° specimen, and 4% higher strength of the lay-up direction specimen with X-Plus. The bed temperature had a minor effect on tensile strength.

Reinforcing in the lay-up direction with self-heating for carbon fiber composites fabricated using a fused filament fabrication 3D printer

In recent times, 3D printers have been employed to fabricate continuous fiber composites. The 3D-printed composites fabricated via fused filament fabrication have no reinforcing fibers in the lay-up direction, resulting in low stiffness and strength in this direction. In the present study, a simple method to reinforce the lay-up direction of 3D-printed composites is proposed. First, a composite part with a through rectangular hole is fabricated via 3D printing. A rectangular reinforcing bar with continuous carbon fibers is then printed separately. Subsequently, the reinforcing bar is inserted into the through hole. A large electric current is applied to the carbon fibers in the reinforcing bar, and the surface thermoplastic polymer is melted via resistive heating (self-heating). As a result, the bar becomes fused to the part, which increases the stiffness and strength of the part. Tensile test and bending test specimens in the lay-up direction were fabricated using commercially available 3D printers. The results show that the simple reinforcing method effectively improves the mechanical properties of the part in the lay-up direction.

The influence of different compositions of fiber metal laminates on the fracture in the semi-solidified stamping forming

Fiber metal laminates (FMLs) are widely used in manufacturing due to the high specific strength, fatigue resistance, and lightweight. However, because of the deformation coordination of different layers of FMLs, challenges have been faced in rapid and small part forming. To research the feasibility of the fast forming of small parts using the FMLs, the influence of different compositions of FMLs on the stamping performance under the semi-solidified process condition was investigated, including the outer aluminum layer, the fiber lay-up direction in the middle layer, and the various states of the resin. Based on the results of Finite-element simulation and experiments, the semi-solidified process can improve the forming performance of FMLs by making the thickness distribution of the outer aluminum layers more uniform and preventing excessive fiber deformation. The coordination of fiber lay-up direction and interlayer forces can improve the forming limit height of semi-solidified FMLs. Besides, the fracture position of the cup part is related to the fiber lay-up direction and interfacial bonding performance in FMLs. This study provides necessary guidance for the rapid stamp forming of small parts using FMLs.

Formability Analysis of Fiber Metal Laminates with Different Core and Skin Layers by Stamping Process

Fiber metal laminates (FMLs) are widely used in aerospace industry due to their unique high specific strength, fatigue resistance, corrosion resistance and other excellent characteristics. Thermosetting FMLs is generally used for forming large size parts and rarely used as raw material for producing small size and complex shape parts. This study attempts a methodology that stamping thermosetting FMLs to form cylinder shape parts before the curing process. The forming limit height of FMLs were analyzed by choosing different core materials, layup direction and skin layer thickness. And through the optimization of these variables, a better-quality part has been formed.

Mechanical properties of Ti/CF/PMR polyimide fiber metal laminates with various layup configurations

The mechanical properties of Ti/CF/PMR polyimide fiber metal laminates (FMLs) with various layup configurations and fiber layer orientations (0°, 90°, and ±45°) were systematically investigated. The results suggest that the elastic modulus and tensile strength of the FMLs were determined by the interfacial adhesion, volume fraction, and layup direction of the carbon fibers. A model has been proposed herein to predict the corresponding relative tensile strengths. The FML specimens were subjected to the compressive stress on the upper surface and tensile stress on the lower surface under the function of flexural strength, while the delamination and local buckling failure occupied the main position. Interlaminar shear strength (ILSS) of the FMLs with surface-coated pretreatment was higher than that of the untreated specimens. The applied load was effectively transferred to the carbon fibers via polyimide resin. Then, the axial load was transferred to the adjacent fibers having the same orientation. The ILSS of unidirectional layered FMLs had the highest value, while that of FMLs with carbon fibers laminated at ±45° was relatively low. The interlaminar shear fracture tended to occur inside the layers oriented in the direction of maximum load or in the vicinity of such layers.

Tensile property evaluations of 3D printed continuous carbon fiber reinforced thermoplastic composites

Continuous carbon fiber composites can be printed using 3D printers. Many studies detailing the mechanical properties of such 3D printed composites have been published, all of which employed a conventional tensile specimen configuration with surface resin layers. In the present study, 0°, 90°, ±45°, and lay-up direction type specimens have been designed for 3D printed composites without surface layers. Both conventional and newly designed specimens with serpentine folded fiber bundles were fabricated and investigated experimentally using a 3D printer. The lay-up direction specimen was fabricated using 800 layers. The specimens without the serpentine folded fiber bundles were experimentally shown to be adequate for tensile tests. The lay-up direction specimen had the lowest strength and stiffness, which appears to be related to its surface roughness.

SiC fiber reinforced geopolymer composites, part 2: Continuous SiC fiber

In this paper, unidirectional SiC fiber (SiCf) reinforced geopolymer composites (SiCf/geopolymer) were prepared and effects of fiber contents on the microstructure and mechanical properties of the composites in different directions were investigated. The XRD results showed that addition of SiCf retarded geopolymerization process of geopolymer matrix by weakening the typical amorphous hump. SiCf in all the composites were well infiltrated by geopolymer matrix, but microcracks which were perpendicular to the fiber axial direction were noted in the interface area due to the thermal shrinkage of matrix during the curing process. With the increases in fiber contents, although Young's modulus of the composites increased continuously, flexural strength, fracture toughness and work of fracture increased at first, reached their peak values and then decreased. And when fiber content was 20vol%, the composites showed the highest flexural strength, fracture toughness and work of fracture, which were 14.2, 15.2 and 81.6 times as high as those of pristine geopolymer, respectively, indicating significant strengthening and toughening effects from SiCf. Meanwhile, SiCf/geopolymer composites failed in different failure modes in the different directions, i.e., tensile failure mode in the x direction (in-plane and perpendicular to the fiber axial direction) and shear failure mode in the z direction (laminate lay-up direction).

Study on Mechanical Properties of Flax Fibre Textile Reinforced Composites Fabricated Using Bio-Based Epoxy Resin Matrix

Flax fibre reinforced composites were made from non-crimp and woven flax fabric reinforcements using bio-based epoxy resin matrix. The fabrics impregnated with epoxy resin containing 55% biomass carbon were fabricated using vacuum bag technique. The fibre weight content of around 40 wt% was achieved through the vacuum bag technique. The fibre assembly and the morphology of the composites were studied using optical microscope. The influences of different weave type and fibre layup direction on the mechanical properties of composites were studied. It was found that, the woven fabric had lower impact strength values than the unidirectional and biaxial oriented fibres. But the woven fabric had achieved relatively equal impact energies on both directions. The maximum flexural strength (196 MPa) and modulus (13.5 GPa) was observed for the unidirectional non-crimp fabric on 0° fibre layup direction.

Free Vibration Analysis of Fiber Metal Laminate Annular Plate by State-Space Based Differential Quadrature Method

A three-dimensional elasticity theory by means of a state-space based differential quadrature method is presented for free vibration analysis of fiber metal laminate annular plate. The kinds of composite material and metal layers are considered to be S2-glass and aluminum, respectively. A semianalytical approach which uses state-space in the thickness and differential quadrature in the radial direction is implemented for evaluating the nondimensional natural frequencies of the annular plates. The influences of changes in boundary condition, plate thickness, and lay-up direction on the natural frequencies are studied. A comparison is also made with the numerical results reported by ABAQUS software which shows an excellent agreement.

Minimizing Stresses of Layer Composites by Controlling the Interface Geometry

One of the most critical issues of layer composite structures is the induced high stresses at the interfaces due to the property mismatch of the layers. In the previous attempts to reduce these stresses, the interfaces are considered as flat surfaces perpendicular to the lay-up direction of the layers. The objective of this article is to minimize these stresses by proposing other forms of the interface geometry, such as curved surface and flat surface inclined on the lay-up direction of the layers. It is found that the induced highest stress can be reduced greatly by considering the proposed interface geometries.

Tribological Properties of Carbon/PEEK Composites

In this study, the effect of Carbon/PEEK composites on the tribological properties has been investigated. Also, its validity has been tested in the capacity of alternative materials of the Ti-based materials used for artificial hip joint. Moreover, this work evaluated the mechanical properties according to the fiber ply orientation, along with the fractured surfaces of the carbon/PEEK composites. The composites with a unidirectional orientation had higher tribological properties than those with a multidirectional orientation. This was caused by the debonding between the carbon fiber and the PEEK, which was proportional to the contact area between the sliding surface and the carbon fiber. The friction test results showed that there were no significant differences in relation to the fiber ply orientation. However, the friction properties of the carbon/PEEK composites were higher than those of the carbon/epoxy composites. In addition, the results showed that a composite that slid in a direction normal to the prepreg lay-up direction had a smaller friction coefficient than one that slid in a direction parallel to the prepreg lay-up direction.

Detection of Fibre Waviness Using Ultrasonic Array Scattering Data

Composite materials owe their success to the ability to favour mechanical properties in specific directions whilst minimising the weight of components. Although the composite manufacturing process has been progressively improved, subtle defects such as fibre waviness are still commonplace. Any localised departure of a ply from the desired lay-up direction is known to adversely affect strength. Therefore, manufacturers and end users are interested in detecting defects such as fibre waviness at various stages during prototyping and as part of the manufacturing process.

High-resolution Ultrasonic Imaging Evaluation and Behavior Analysis of Impact Damages in Composites

Impact damage is a harmful defect, which is easily induced in composite structures during manufacturing and in-service. Impulse ultrasonic wave reflections in carbon fiber-reinforced composites(CFRC) are analyzed. Ultrasonic surface dead-zone(USDZ) and lateral resolution(LR) can be improved markedly when time-width of probe pulse(TWOPP) is decreased reasonably and its property is polished appropriately. The datum about depth and size of impact damages in CFRC body can be extracted from ultrasonic reflected signals at damages and their time-of-flight(TOF). B-scan and C-scan in depth(or T-scan) imaging techniques based on the investigated high-resolution ultrasonic method are employed to explore the details and to carry out visualized inspection and quantitative evaluation of impact damages induced in CFRC laminated specimens. Experimental results have shown that time-resolved reflections resulted from defects nearby CFRC specimen surface can be obtained distinctly when their TOFs are close to the half of TWOPP and probe pulse has a single duration in time domain. In this case, the USDZ and LR can be approximately reached to the thickness of a single pre-preg ply of CFRC laminate, i.e., 0.13 mm. The distribution and development as well as depth of impact damages in cross-section of the CFRC laminated specimens can be seen well by using serials of B-scan imaging technique.The quantitative information about impact damage zone and size along layup direction of CFRC laminated specimens can be excavated and determined exactly by using ultrasonic T-scan imaging method. The combination of the two kinds of imaging methods provides a powerful imaging and quantitative approaches for evaluation of impact damage as well as visual exploring 3D behavior of impact damage in CFRC laminates.

Effect of Fiber Lay-Up Direction Misalignment on the Natural Frequency of Composite Laminates

With the extensive use of composite materials in aviation industry, the research of factors which affect their basic performances in production and usage has become very important. In this paper, a finite element analysis model is built by the commercial software MSC.Nastran / Patran to research the effect of fiber lay-up direction misalignment on the natural frequency of composite laminates. The results show that, in the same boundary conditions, stacking sequence has a significant impact on the natural frequencies and vibration modes of composite laminates, and in the lay-up process, the natural frequency change of laminates caused by 0° fiber lay-up direction misalignment is much larger than the natural frequency change of laminates due to 90° fiber lay-up direction misalignment. In the process control and certification of composite laminate plates lay-up, special attention should be taken to the inspection of 0° direction fibers.

Compressive failure strengths and modes of woven S2-glass reinforced polyester due to quasi-static and dynamic loading

Abstract The failure strengths and modes of the woven S2-glass reinforced polyester thick laminate are characterized through a comprehensive set of experiments. Compression strength tests in different directions were performed, and optical and scanning electron microscopy studies of the fractured specimen surfaces were conducted. The failure modes are complex involving a combination of failure mechanisms. The failure stresses and strains in the ply lay-up direction were higher than those in the plane of the lamina. The material's dynamic response was determined using both the split Hopkinson pressure bar and the direct disk impact techniques. The material was found to be significantly strain rate sensitive.