RATE-DEPENDENT COMPACTION AND RELAXATION RESPONSE OF UNCURED PREPREGS UNDER HIGH-PRESSURE CONDITIONS

2021 ◽  
Author(s):  
NOORA ALAHMED ◽  
KAMRAN KHAN ◽  
REHAN UMER
Keyword(s):  
Stress Relaxation ◽  
Composite Structures ◽  
Volume Fraction ◽  
Permanent Deformation ◽  
Applied Pressure ◽  
Displacement Rate ◽  
Relaxation Response ◽  
Void Content ◽  
Fiber Volume ◽  
Rate Dependent

The compaction-relaxation response at different compaction rates and fiber volume fractions plays a key role in understanding the viscoelastic response of uncured prepregs. Hence, this study characterizes the time-dependent behavior of un-cured 4- layer prepregs subjected to compaction-stress relaxation test at different displacement rates i.e., 0.1 mm/min, 1.0 mm/min, and 10 mm/min, at 0.65 fiber volume fraction and allowed to relax for two hours. In this study, the complete deformation history of the Hexply M26T multilayer prepregs is measured from a stress-free state to the cured state. The effects of rate-dependent compaction-relaxation at different rates on percentages of compaction, recovery, stress change during relaxation, and permanent deformation of prepregs are computed. It was concluded that the 0.1   /    displacement rate showed the lowest peak stress level and the lowest stress relaxation and permanent deformation. A viscoelastic model was used to fit the experimental data and the results showed a good agreement. The void content was determined analytically and from the XCT-aided geometrical model. It was observed that for a given test condition, the void content increases as the displacement rate increases, due to the high applied pressure. This study highlights the importance of rate-dependent compaction-relaxation behavior and the need to determine the suitable process parameters and models to manufacture high-quality aerospace composite structures.

QUASI-LINEAR VISCOELASTIC MODELLING OF UNCURED PREPREGS UNDER COMPACTION

2021 ◽  
Author(s):  
SIDDHESH S. KULKARNI ◽  
KAMRAN A. KHAN ◽  
REHAN UMER
Keyword(s):  
Stress Relaxation ◽  
Relaxation Function ◽  
Soft Tissues ◽  
Volume Fraction ◽  
Time Dependent ◽  
Strain History ◽  
Manufacturing Processes ◽  
Fiber Volume ◽  
Consolidation Process ◽  
Thermoset Resin

Reinforcement compaction sometimes referred as consolidation process and is one of the key steps in various composite manufacturing processes such as autoclave and out-of-autoclave processing. The prepregs consist of semi-cured thermoset resin system impregnating the fibers. hence, the prepreg shows strong viscoelastic compaction response, which strongly depends on compaction speed and stress relaxation. modeling of time-dependent response is of utmost importance to understand the behavior of prepregs during different stages of composites manufacturing processes. The quasilinear viscoelastic (QLV) theory has been extensively used for the modeling of viscoelastic response of soft tissues in biomedical applications. In QLV approach, the stress relaxation can be expressed in terms of the nonlinear elastic function and the reduced relaxation function. The constitutive equation can be represented by a convolution integral of the nonlinear strain history, and reduced relaxation function. This study adopted a quasilinear viscoelastic modeling approach to describe the time dependent behavior of uncured-prepregs under compression. The model was modified to account for the compaction behavior of the prepreg under a compressive load. The deformation behavior of the prepreg is usually characterized by the fiber volume fraction, V . In this study, the material used was a 2/2 Twill weave glass prepreg (M26T) supplied by Hexcel® Industries USA. We performed a compaction experiment of the uncured prepreg at room temperature at different displacement rate and subsequent relaxation to describe the viscoelastic behavior of the prepreg. The model parameter calibration was performed using the trust-region-reflective algorithm in matlab to a selected number of test data. The calibrated model was then used to predict the rate dependent compaction and relaxation response of prepregs for different fiber volume fractions and strain rates.

Biomimetic composites inspired by venous leaf

2017 ◽  
Vol 52 (3) ◽  
pp. 361-372 ◽  
Author(s):  
Gongdai Liu ◽  
R Ghosh ◽  
A Vaziri ◽  
A Hossieni ◽  
D Mousanezhad ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Yield Stress ◽  
Poisson’S Ratio ◽  
Composite Structures ◽  
Volume Fraction ◽  
Matrix Material ◽  
Poisson's Ratio ◽  
Fiber Volume ◽  
Young’S Moduli

A typical plant leaf can be idealized as a composite having three principal fibers: the central mid-fiber corresponding to the mid-rib, straight parallel secondary fibers attached to the mid-fiber representing the secondary veins, and then another set of parallel fibers emanating from the secondary fibers mimicking the tertiary fibers embedded in a matrix material. This paper introduces a biomimetic composite design inspired by the morphology of venous leafs and investigates the effects of venation morphologies on the in-plane mechanical properties of the biomimetic composites using finite element method. The mechanical properties such as Young’s moduli, Poisson’s ratio, and yield stress under uniaxial loading of the resultant composite structures was studied and the effect of different fiber architectures on these properties was investigated. To this end, two broad types of architectures were used both having similar central main fiber but differing in either having only secondary fibers or additional tertiary fibers. The fiber and matrix volume fractions were kept constant and a comparative parametric study was carried out by varying the inclination of the secondary fibers. The results show that the elastic modulus of composite in the direction of main fiber increases linearly with increasing the angle of the secondary fibers. Furthermore, the elastic modulus is enhanced if the secondary fibers are closed, which mimics composites with closed cellular fibers. In contrast, the elastic modulus of composites normal to the main fiber ( x direction) exponentially decreases with the increase of the angle of the secondary fibers and it is little affected by having secondary fibers closed. Similar results were obtained for the yield stress of the composites. The results also indicate that Poisson’s ratio linearly increases with the secondary fiber angle. The results also show that for a constant fiber volume fraction, addition of various tertiary fibers may not significantly enhance the mechanical properties of the composites. The mechanical properties of the composites are mainly dominated by the secondary fibers. Finally, a simple model was proposed to predict these behaviors.

Resin Infusion of Triaxially Braided Preforms With Through-the-Thickness Reinforcement

2001 ◽  
Author(s):  
Jay R. Sayre ◽  
Alfred C. Loos
Keyword(s):  
Composite Structures ◽  
High Performance ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Element Model ◽  
Manufacturing Cost ◽  
Fiber Volume ◽  
Resin Infusion ◽  
Infiltration Process ◽  
High Fiber

Abstract Vacuum assisted resin transfer molding (VARTM) has shown potential to significantly reduce the manufacturing cost of high-performance aerospace composite structures. In this investigation, high fiber volume fraction, triaxially braided preforms with through-the-thickness stitching were successfully resin infiltrated by the VARTM process. The preforms, resin infiltrated with three different resin systems, produced cured composites that were fully wet-out and void free. A three-dimensional finite element model was used to simulation resin infusion into the preforms. The predicted flow patterns agreed well with the flow pattern observed during the infiltration process. The total infiltration times calculated using the model compared well with the measured times.

Micro-computed tomography analysis of natural fiber and bio-matrix tubular-braided composites

2019 ◽  
Vol 53 (28-30) ◽  
pp. 4003-4013 ◽  
Author(s):  
Brianna M Bruni-Bossio ◽  
Garrett W Melenka ◽  
Cagri Ayranci ◽  
Jason P Carey
Keyword(s):  
Computed Tomography ◽  
Natural Fiber ◽  
Volume Fraction ◽  
Void Content ◽  
Micro Computed Tomography ◽  
Braided Composites ◽  
Fiber Volume ◽  
Increasing Demand ◽  
Materials Used ◽  
Curing Method

There is an increasing demand for the use of “green”-based materials as reinforcement and matrix materials in composites. However, the ability of these natural-based materials to perform as consistently and reliably as conventional materials is still relatively unknown. A key importance in the viability of these materials is the evaluation of the content of voids and imperfections, which may affect the properties of the entire composite. In this study, the microstructure of tubular-braided composites manufactured from cellulose fibers and a partially bio-derived resin was studied with the use of micro-computed tomography. These methods were used to determine the effect of modifying braid angle, resin type, and curing method on fiber volume fraction, void volume, and void distribution. It was determined that the void content increased with the increase in braid angle, and vacuum-bagging reduced the total void content. The sample with the smallest braid angle produced with vacuum-bagged curing contained a void fraction of 1.5%. The results of this study proved that the materials used could be viable for further testing and development and that micro-computed tomography imaging is valuable for identifying how to improve consistency and minimize imperfections to create more accurate and reliable natural fiber-braided composites.

Pressurized Infusion: A New and Improved Liquid Composite Molding Process

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
M. Akif Yalcinkaya ◽  
Gorkem E. Guloglu ◽  
Maya Pishvar ◽  
Mehrad Amirkhosravi ◽  
E. Murat Sozer ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Composite Laminates ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Compaction Pressure ◽  
External Pressure ◽  
Void Content ◽  
Liquid Composite Molding ◽  
Molding Process ◽  
Fiber Volume

Vacuum-assisted resin transfer molding (VARTM) has several inherent shortcomings such as long mold filling times, low fiber volume fraction, and high void content in fabricated laminates. These problems in VARTM mainly arise from the limited compaction of the laminate and low resin pressure. Pressurized infusion (PI) molding introduced in this paper overcomes these disadvantages by (i) applying high compaction pressure on the laminate by an external pressure chamber placed on the mold and (ii) increasing the resin pressure by pressurizing the inlet resin reservoir. The effectiveness of PI molding was verified by fabricating composite laminates at various levels of chamber and inlet pressures and investigating the effect of these parameters on the fill time, fiber volume fraction, and void content. Furthermore, spatial distribution of voids was characterized by employing a unique method, which uses a flatbed scanner to capture the high-resolution planar scan of the fabricated laminates. The results revealed that PI molding reduced fill time by 45%, increased fiber volume fraction by 16%, reduced void content by 98%, improved short beam shear (SBS) strength by 14%, and yielded uniform spatial distribution of voids compared to those obtained by conventional VARTM.

scholarly journals Bending Flexibility of Moso Bamboo (Phyllostachys Edulis) with Functionally Graded Structure

Materials ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2007 ◽  
Author(s):  
Xin Wei ◽  
Haiying Zhou ◽  
Fuming Chen ◽  
Ge Wang
Keyword(s):  
Composite Structures ◽  
Volume Fraction ◽  
Critical Role ◽  
Bending Stiffness ◽  
Functionally Graded ◽  
Size Difference ◽  
Vascular Bundles ◽  
Phyllostachys Edulis ◽  
Fiber Volume ◽  
Sustainable Resources

As one of the most renewable and sustainable resources on Earth, bamboo with its high flexibility has been used in the fabrication of a wide variety of composite structures due to its properties. A bamboo-based winding composite (BWC) is an innovative bamboo product which has revolutionized pipe structures and their applications throughout China as well as improving their impact on the environment. However, as a natural functionally graded composite, the flexibility mechanism of bamboo has not yet been fully understood. Here, the bending stiffness method based on the cantilever beam principle was used to investigate the gradient and directional bending flexibility of bamboo (Phyllostachys edulis) slivers under different loading Types during elastic stages. Results showed that the graded distribution and gradient variation of cell size of the fibers embedded in the parenchyma cells along the thickness of the bamboo culm was mainly responsible for the exhibited gradient bending flexibility of bamboo slivers, whereas the shape and size difference of the vascular bundles from inner to outer layers played a critical role in directional bending flexibility. A validated rule of mixture was used to fit the bending stiffness under different loading Types as a function of fiber volume fraction. This work provides insights to the bionic preparation and optimization of high-performance BWC pipes.

Refinement of the Thermal Press Curing Process for Advanced Composites

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Jaron Kuppers ◽  
Daniel Walczyk
Keyword(s):  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Center Of Pressure ◽  
Applied Pressure ◽  
Hydraulic Press ◽  
Maximum Temperature ◽  
Thickness Variation ◽  
Fiber Volume ◽  
Tool Surface ◽  
Temperature And Pressure

Thermal press curing (TPC) is an alternative process to autoclaving for consolidating and curing thermoset and thermoplastic prepreg composite parts by pressing them between a heated “curing mold” and a customized rubber-faced “base mold” that are engineered to provide uniform temperature and pressure conditions. A study was performed with a kayak paddle part made from eight plies of woven carbon/epoxy prepreg material and formed by double diaphragm forming (DDF). The study expounds on the narrow body of TPC knowledge around three main objectives: (1) to experimentally compare TPC cured parts to a benchmark autoclave process using a realistic part shape with fine geometrical details, (2) to evaluate the necessity of vacuum bagging of TPC cured parts, and (3) to characterize the robustness/sensitivities of pressure application during the TPC process by varying both the total pressure applied to the base mold and the location the hydraulic press ram applied pressure to the base mold. Maximum temperature and pressure variations around the target levels over the entire clamped tool surface were measured as 5.0 °C and 5.5%, respectively, both of which were well within the manufacturer's recommendations. The TPC part had fewer defects, was generally thinner, and had a higher fiber volume fraction than a comparable autoclaved part. Little difference was observed between the TPC parts made with and without vacuum bagging. Parts with too little pressure (90%) resulted in more thickness variation and defects than too much pressure (110%). Finally, TPC parts exhibit some thickness variation, as expected, when ram force is applied off the center of pressure (COP).

scholarly journals Formation of Resin-Rich Zones in Composites Processing

2010 ◽  
Vol 123-125 ◽  
pp. 543-546 ◽  
Author(s):  
Chen Song Dong ◽  
Tze Chiun Tsai
Keyword(s):  
Composite Structures ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Liquid Composite Molding ◽  
Fiber Volume ◽  
Factors Affecting ◽  
Composite Molding ◽  
Composites Processing ◽  
Stress And Deformation ◽  
Fiber Preforms

Resin-rich zones are a common phenomenon in liquid composite molding processes. These resin-rich zones cause unwanted residual stress and deformation, and part-to-part variation, and thus they need to be studied in the design of composite structures. An experimental study on the formation of resin-rich zones in angled composite parts is presented in this paper. Two open-channel mold sets were designed and fabricated. Fiber preforms were loaded into these molds and the gaps formed were visually inspected by a microscope. The influences of corner radius, fiber volume fraction, enclosed angle, and stacking sequence were investigated, and significant factors affecting gap thickness were identified by Design of Experiments (DOE). It can be concluded from the experimental results that: 1) Fiber volume fraction is the most significant factor affecting gap thickness. Gap thickness is inversely proportional to fiber volume fraction; 2) Gap thickness is inversely proportional to radius; 3) The gap thickness of unidirectional preforms is larger than that of the cross-ply preforms.

Effects of vacuum pressure, inlet pressure, and mold temperature on the void content, volume fraction of polyester/e-glass fiber composites manufactured with VARTM process

2011 ◽  
Vol 45 (26) ◽  
pp. 2727-2742 ◽  
Author(s):  
Vishwanath R. Kedari ◽  
Basil I. Farah ◽  
Kuang-Ting Hsiao
Keyword(s):  
Glass Fiber ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Fiber Composite ◽  
Mold Temperature ◽  
Vacuum Pressure ◽  
Inlet Pressure ◽  
Void Content ◽  
Fiber Volume ◽  
Vartm Process

Vacuum-assisted resin transfer molding (VARTM) process is one of the liquid composite molding (LCM) processes aimed at producing high-quality composite parts. The void content and fiber volume fraction of a VARTM part can be affected by many parameters and is critical to the mechanical properties and the quality of the part. In this paper, a series of experiments were conducted with a heated dual pressure control VARTM setup for investigating the effects of vacuum pressure, inlet pressure, and mold temperature on the void content and fiber volume fraction of polyester/E-glass fiber composite. It was found that stronger vacuum and higher mold temperature can better control and increase the fiber volume fraction; however, such a combination of strong vacuum and high mold temperature may also require a reduced inlet pressure for minimizing the void content. The need of pressure reduction can be explained with the compatibility between Darcy's flow and capillary flow in the fiber preform and can be calculated based on the room temperature VARTM results. The experimental results suggest that high mold temperature, high vacuum, and appropriately reduced inlet pressure can produce a VARTM part with high fiber volume fraction and low void content.

Processing Effects on Formation of Microvoids and Hydraulic Fluid Absorption of Quartz/BMI Laminates

2015 ◽  
Author(s):  
Keith R. Hurdelbrink ◽  
Jacob P. Anderson ◽  
Zahed Siddique ◽  
M. Cengiz Altan
Keyword(s):  
Mechanical Properties ◽  
Relative Humidity ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Void Content ◽  
Hydraulic Fluid ◽  
Processing Conditions ◽  
Fluid Absorption ◽  
Fiber Volume ◽  
Fluid Content

Bismaleimide (BMI) resin with Quartz (AQ581) fiber reinforcement is desirable for systems requiring a high glass transition temperature, low dielectric properties, and high laminate mechanical properties. These properties make quartz/BMI an ideal composite material for complex aerospace structures, and are currently being used in various aircraft engine cowlings and radomes. In addition to moisture absorption, quartz/BMI composite laminates are often exposed to different types of hydraulic fluid contaminants, which may lead to anomalous absorption behavior over the service life of the composite structure. Variations in laminate processing conditions, such as prepreg preconditioning and fabrication cure pressure, can have a significant effect on microstructural features of fiber-reinforced composites. Microstructural features, such as fiber volume fraction and void content, can influence mechanical properties and long term absorption of moisture or other liquid contaminants. In this paper, the process-induced microstructure and hydraulic fluid absorption behavior of quartz/BMI laminates are presented. The laminates are fabricated from preconditioned prepregs and cured at different pressures to generate different levels of microvoids, while keeping the fiber volume fraction constant. Location, size and morphology of microvoids are investigated via SEM images obtained from laminates cured at different processing conditions. Composite samples were prepared and fully-immersed in hydraulic fluid at room temperature, and were not subjected to any prior degradation. The laminate samples immersed in hydraulic fluid exhibited clear non-Fickian absorption behavior, which was successfully predicted by the one-dimensional Hindered Diffusion Model (HDM). The degree of non-Fickian absorption behavior, or hindrance coefficient (μ), ranged from 0.30 to 0.72. Model prediction indicates that as the fabrication pressure increased, the maximum fluid content (M∞) decreased considerably. Additionally, a reduction in maximum fluid content was observed when lower relative humidity environments were used for prepreg preconditioning. A discernable difference was not observed in the absorption dynamics when the prepregs were preconditioned at greater than 70% relative humidity.

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