Effect of random vibration processing on void content in composite laminates

2018 ◽  
Vol 40 (8) ◽  
pp. 3122-3130 ◽  
Author(s):  
Xiaobo Yang ◽  
Lihua Zhan ◽  
Chengbiao Jiang ◽  
Xing Zhao ◽  
Chenglong Guan
Keyword(s):  
Composite Laminates ◽  
Random Vibration ◽  
Void Content

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.

Infra-Red Thermography based Inspection of Hybrid Composite Laminates under Flexure Loading

2018 ◽  
Vol 10 (1) ◽  
Author(s):  
R. Bhoominathan ◽  
P. Divyabarathi ◽  
R. Manimegalai ◽  
T. Nithya ◽  
S. Shanmugapriya
Keyword(s):  
Composite Laminates ◽  
Volume Fraction ◽  
Void Content ◽  
Destructive Testing ◽  
Flexural Loading ◽  
Infra Red ◽  
Before And After ◽  
Cfrp Composite ◽  
Structural Parts ◽  
Non Destructive

Generally, the aircraft structural parts are economically high in cost so the materials need to be inspected for defects or damages using various non-destructive testing (NDT) methods like ultrasonic, thermography and acoustic emission. The aim of this project is to characterize the defects in composite laminates before and after the flexural loading using infra-red thermography NDT method. GFRP and hybrid (GFRP+CFRP) composite laminates are fabricated with different orientation such as uni-directional, cross ply, anti-symmetric and angle ply and then tested under flexural loading according to ASTM D790 standard. The volume fraction of the fibre and matrix needs to be found out to know the void content and the mixing ratio of reinforcement and binder.

Detection of Voids in Carbon/Epoxy Laminates and Their Influence on Mechanical Properties

2017 ◽  
Vol 25 (5) ◽  
pp. 371-380 ◽  
Author(s):  
Luca Di Landro ◽  
Aurelio Montalto ◽  
Paolo Bettini ◽  
Stefania Guerra ◽  
Fabrizio Montagnoli ◽  
...  
Keyword(s):  
Composite Laminates ◽  
Mechanical Performance ◽  
Thermal Analyses ◽  
Void Content ◽  
Processing Conditions ◽  
Micro Computed Tomography ◽  
Sem Image ◽  
Beam Shear ◽  
Mechanical Performances ◽  
Curing Cycle

Defects, such as voids and delaminations, may significantly reduce the mechanical performance of components made of composite laminates. Distributed voids and porosity are generated during composite processing and are influenced by prepreg characteristics as well as by curing cycle parameters. On the basis of rheological and thermal analyses, as well as observations of laminates produced by different processing conditions, curing pressure appears the most influent factor affecting the void content. This work compares different methods for void analysis and quantitative evaluation (ultrasonic scan, micro-computed tomography, acid digestion, SEM image analysis) evidencing their applicative limitations. Carbon/epoxy laminates were produced in autoclave or oven by vacuum bag technique, using different processing conditions, so that void contents ranging from 0% to 7% volume were obtained. Effects of porosity over laminates mechanical performances are analysed. The results of tensile and compressive tests are discussed, considering the effect that different curing cycles have over void content as well as over fibre/resin fraction. Interlaminar strength, as measured by short beam shear tests, which is a matrix-dominated property, exhibits a reduction of failure strength up to 25% in laminates with the highest void content, compared to laminates with no porosity.

Predicting Formation of Manufacturing Defects in Contoured Composites

2019 ◽  
Vol 64 (4) ◽  
pp. 1-15 ◽  
Author(s):  
Guillaume Seon ◽  
Yuri Nikishkov ◽  
Andrew Makeev ◽  
Lauren Fergusson
Keyword(s):  
Finite Element ◽  
Manufacturing Process ◽  
Composite Laminates ◽  
Defect Formation ◽  
Radius Of Curvature ◽  
Void Content ◽  
Consolidation Process ◽  
Closed Cavity ◽  
Manufacturing Defects ◽  
Early Stages

Composite helicopter rotor components are typically thick and often have areas with a tight radius of curvature, which make them especially prone to process-induced defects, including wrinkles and voids at ply interfaces. Such flaws cause high rejection rates in production of flight-critical components and structures. This work seeks to fill the gaps in understanding generation of the noted defects in contoured polymer–matrix composite laminates. In particular, understanding and modeling defect formation at the early stages of the manufacturing process might be the missing link to enable the development of practical engineering solutions allowing for better control of the manufacturing process of contoured composite parts. In this work, an approach based on a continuum description of the uncured prepreg material, including the initial bulk or void content, and finite element modeling (FEM) is used to simulate the consolidation process at the early stages of manufacturing of contoured laminates. The simulation predicts instabilities leading to formation of both wrinkles and voids at ply interfaces during laminate debulking or vacuum consolidation. Applicability of the method to consolidation in both closed-cavity and open-face tooling is also demonstrated. FEM results show good correlation with X-ray computed tomography data. This work also introduces a new simulation concept based on finite element and discrete modeling of voids at ply interfaces to improve the accuracy of predicting their evolution during the debulking operations.

Void reduction in VARTM composites by compaction of dry fiber preforms with stationary and moving magnets

2018 ◽  
Vol 53 (6) ◽  
pp. 769-782 ◽  
Author(s):  
Mehrad Amirkhosravi ◽  
Maya Pishvar ◽  
M Cengiz Altan
Keyword(s):  
Composite Laminates ◽  
Volume Fraction ◽  
Compaction Pressure ◽  
Void Content ◽  
Novel Method ◽  
Improved Performance ◽  
Small Parts ◽  
Induced Defects ◽  
Fiber Preforms

Voids are the most common process-induced defects in composite laminates fabricated by vacuum assisted resin transfer molding (VARTM). Reduction or total elimination of these defects is essential for the improved performance and long-term durability of the structural composites. This study introduces a novel method that reduces the void content in VARTM laminates to below 1% by compacting the fibrous mat before infusion. The compaction is achieved by applying magnetic pressure on the vacuum bag by either stationary or moving magnets which are removed before the resin infusion. To assess the effectiveness of the proposed method, 6-, 12-, and 18-ply random mat glass/epoxy laminates are fabricated by VARTM using compacted and uncompacted mats and their properties are compared. In addition, different sets of magnets are used to investigate the effect of compaction levels on the resin flow and the quality of the final part. The placement of stationary magnets on the entire vacuum bag surface is practical for fabrication of small parts. For medium to large parts, however, magnets with a smaller footprint can be moved to apply the compaction pressure over a larger vacuum bag surface. The results show that by applying compaction pressure of 0.2 MPa or higher either by stationary or moving magnets on the dry preforms, the void volume fraction was decreased by 65%–95% to 0.1%–0.8% in all laminates.

Critical Void Content for Polymer Composite Laminates

AIAA Journal ◽  
2005 ◽  
Vol 43 (6) ◽  
pp. 1336-1341 ◽  
Author(s):  
Michelle Leali Costa ◽  
Sergio Frascino Muller de Almeida ◽  
Mirabel Cerqueira Rezende
Keyword(s):  
Polymer Composite ◽  
Composite Laminates ◽  
Void Content ◽  
Critical Void

Cure kinetics and autoclave-pressure dependence on physical and mechanical properties of woven carbon/epoxy 8552S/AS4 composite laminates

2021 ◽  
pp. 096739112110284
Author(s):  
Abd Baghad ◽  
Khalil El Mabrouk ◽  
Sébastien Vaudreuil ◽  
Khalid Nouneh
Keyword(s):  
Mechanical Properties ◽  
Composite Laminates ◽  
Treatment Time ◽  
Physical And Mechanical Properties ◽  
Cure Kinetics ◽  
Void Content ◽  
Scanning Calorimetry ◽  
Microstructure And Mechanical Properties ◽  
The Matrix ◽  
Interlaminar Shear

The final mechanical properties of composite laminates are highly dependent on their curing cycles in the autoclave. During this cycle, the temperature, pressure, vacuum, and treatment time will influence the quality of manufactured parts. The void content is considered the most harmful defects in carbon/epoxy laminates since they weaken the matrix-dominated mechanical properties such as interlaminar shear and compressive strengths. In the present work, differential scanning calorimetry is used to characterize the influence of time/temperature on the behavior of the epoxy resin. Then, a series of [0/90/−45/+45]s laminates composites are autoclave-cured under various applied pressures to evaluate their impact on microstructure and mechanical properties. The interlaminar shear modulus, interlaminar shear strength, laminate compressive modulus, and laminate compressive strength at room and operating engine temperature were measured. The correlation between microstructure and mechanical properties was also studied. The mechanical properties of manufactured carbon/epoxy laminates are found to be dependent on pressure and microstructure. These results are explored to establish an optimal autoclave pressure route that would minimize porosity without counterbalancing mechanical properties.

Effects of cure cycles on void content and mechanical properties of composite laminates

2006 ◽  
Vol 73 (3) ◽  
pp. 303-309 ◽  
Author(s):  
Ling Liu ◽  
Bo-Ming Zhang ◽  
Dian-Fu Wang ◽  
Zhan-Jun Wu
Keyword(s):  
Mechanical Properties ◽  
Composite Laminates ◽  
Void Content

Effect of Vibrations on Void Content in Composite Materials

2008 ◽  
Vol 32 ◽  
pp. 145-148 ◽  
Author(s):  
Jelena Muric-Nesic ◽  
Z. Stachurski ◽  
Paul Compston ◽  
N. Noble
Keyword(s):  
Composite Materials ◽  
Composite Laminates ◽  
Vinyl Ester ◽  
Sandwich Composite ◽  
Void Content ◽  
Vinyl Ester Resin ◽  
Mechanical Vibrations ◽  
Sandwich Composite Structure ◽  
Poor Adhesion

Eliminating common defects such as voids, bubbles and poor adhesion at interfaces will increase the quality of laminated sandwich composite structure. We are experimenting and analyzing the effect of mechanical vibrations applied to the curing system of composite materials production, particularly on minimizing void content. The range of frequency of vibrations covered was from 2Hz to 8kHz, for different period of vibrations. The composite laminates were made by hand lay-up using glass fibres and vinyl-ester resin, and examined under a microscope to determine types and quantity of defects. The results showed reduction in the number of bubbles (as well as in void content) at frequencies between 10Hz and 50Hz for 30 minutes of vibrations.

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