Fabric Plies Research Articles

The effect of ply folds as manufacturing defect on the fatigue life of CFRP materials

Manufacturing defects are inherent to any manufacturing process. However, in composite materials they might be unavoidable, e.g. ply waviness or even folds of plies are present in complex shaped parts during high pressure resin transfer molding of carbon fiber reinforced polymers. In this work, the effect of the ply folds on the fatigue life of the composite material is investigated. Folds along fiber direction (as they commonly appear during manufacturing) were artificially introduced in unidirectional non crimp fabric plies. The target of this study is the prediction of damage initiation due to this particular type of manufacturing defect. The folds locally increase the fiber volume fraction and also introduce resin rich areas. Fatigue tests in fiber direction and transverse to fiber direction are performed at different load ratios under constant amplitude loading. The influence of the defect geometry on damage initiation and progression is investigated at different scales by non-destructive methods before testing, continuous strain measurement and monitoring the damage progression during testing and fractography analysis after final failure. Most of the time, the first damage was observed at the location of the introduced fold for all considered load cases. However, it was also found, that the folds lead to no significant reduction in fatigue life.

Mechanistic cutting force modelling for micro-drilling of CFRP composite laminates

This article presents a mechanistic model to predict thrust force and torque in micro-drilling of carbon fibre-reinforced plastic (CFRP) composite laminates. Tool edge radius effects are considered in this model to predict cutting forces even at low feed values which are comparable to the tool edge radius. As greater fluctuation of cutting force is very common in micro scale machining of composite material due to its layered structure, fabric plies and epoxy resin matrix layers are considered in this model as separate phases rather than as equivalent homogeneous material. Separate sets of cutting coefficients for each phase are determined from the experimental results. The fluctuations of average thrust and torque in alternate layers of fabric plies and epoxy resin matrix are predicted and validated with new experimental results of micro-drilling with a 0.5mm diameter tungsten carbide tool. In both layers, the model predictions are close to the experimental results. Though the prediction errors in epoxy resin matrix are comparatively higher than the errors in fabric plies, these are reasonable considering the complex sub surface damage mechanism due to epoxy resin matrix failure and interfacial debonding.

Flexural and tensile moduli of flexible FR4 substrates

A flexible FR4 substrate is not only a core part of current integrated circuit assemblies, but also a promising material for flexible electronics applications. The thin composite sheet typically contains a single-ply of glass fabric which is impregnated with epoxy resin. The single-ply reinforcement leads to large heterogeneity along the through-thickness direction, which causes different behavior in the flexural and tensile moduli. However, no comparative study between the flexural and tensile moduli has been presented for commercialized flexible FR4 substrates. In this study, the flexural and tensile moduli of flexible FR4 substrates were measured using a three-point bending test and a direct tensile test, respectively. Three FR4 substrates were prepared with a different number of glass fabric plies and different types of epoxy resin, with a total thickness ranging from 100 to 150 μm. The effect of the span-to-depth ratio on the flexural modulus was first examined in order to obtain the true flexural modulus from the three-point bending test. For comparison, the strain was accurately measured using a video extensometer to obtain the tensile modulus. In-plane anisotropy and temperature dependence were also investigated for both the flexural and tensile moduli.

Excellent mechanical properties of carbon fiber semi-aligned electrospun carbon nanofiber hybrid polymer composites

The excellent mechanical properties of carbon fiber fabric hybrid polymer composites is achieved by integrating continuous semi-aligned carbon nanofiber layers in the interlaminar region between carbon fiber fabric plies.

Influence of Temperature on Interlaminar Fracture Toughness of a Carbon Fiber-Epoxy Composite Material

Composite materials have been increasingly used in the aerospace industry for the manufacturing of structures, because of the associated properties of low weight and high mechanical resistance. On the other hand, they have low delamination resistance. This paper presents the results of an experimental study performed to obtain the values of interlaminar fracture toughness (G) of a laminate under three different temperatures, using 0º carbon-epoxy prepreg fabric plies and manufactured via Hand lay up cured in autoclave (HLUP). Double Cantilever Beam (DCB) tests were performed to evaluate mode I toughness, Four Point Bend End Notched Flexure (4ENF) for mode II and Mixed Mode Bending (MMB) for mixed mode I / mode II at -54°C, 25°C and 80°C. The data were collected and analyzed using a routine developed in Matlab®. Finally, the relation between GI and GII through the failure envelope and the temperature influence on the interlaminar fracture toughness was assessed.

Mechanical properties of FRCM using carbon fabrics with different coating treatments

The use of composite materials for repair and retrofit of structures has become a common use among the engineering community. Fabric Reinforced Cementitious Matrix (FRCM) is a composite material specifically designed for masonry and concrete rehabilitation and is becoming a viable alternative to FRP, whenever the project conditions do not allow the use of organic polymer based composites. FRCM is usually constituted by one or multiple plies of dry fabrics (carbon, glass, aramid, basalt or PBO fibers) embedded into an inorganic matrix. If a polymer is used to either cover or bond the fabric strands, such polymer does not fully penetrate and impregnate the fibers as it would for FRP. The purpose of this research work is to study how different types and amounts of organic coatings applied to a carbon fabric could affect the bond behavior between fabric and mortar. The effectiveness of coating treatments was studied by means of direct tensile, pull-off and shear-bond double-lap tests. Experimentation was carried out on different combinations of fabrics and mortars, by varying the levels of pre-impregnation of the fabric during its manufacturing. In addition, the use of a quartz sand layer applied to the fabric after impregnation was investigated. Experimental evidence shows a promising enhancement of the bond between fabric and matrix and, therefore, of the entire system even with the use of low percentages of resin, depending on the type of mortar used.

Performances’ Estimation by Tests of Composite Material Structures With Respect to the Lay-Up Configuration and Mixing the Position of Tape and Fabric Laminae

Abstract This paper presents an estimation of performances by tests on composite material structures. In order to evaluate the effects on the structural behavior, tests changing the percentage of orientation of the fiber at 0, 45 and 90 degrees and mixing the unidirectional plies with the fabric ones have been done. Fixed the lay-up configuration and so the stacking sequence, two typology of structures have been analyzed; the first one having only unidirectional plies while the second one having a fabric ply (plain weave 0/90) in place of the top and bottom unidirectional plies. The openhole compressive strength and the filled-hole tensile strength and moduli have been characterized by test. A total of 72 specimens have been used in the test campaign. In order to well compare the test results a Performance Weight Index (PWI) has been introduced by authors in order to normalize the strength of each laminate with respect to its weight/unit of surface. Results and different laminate behaviors have been evaluated and discussed.

Modeling analysis of fiber hybridization in hybrid glass/carbon composites under high‐velocity impact

The effects of fiber hybridization on damage behavior of hybrid glass/carbon composites under high‐velocity impact were investigated. The Hashin damage model is adopted to model the damage initiation of composites, and the bilinear form of damage evolution law based on the effective displacement is employed. The numerical results show a reasonable agreement with the experimental data. The residual velocity of impact projectile is approximately shown a linearly decreasing trend with the increasing of the thickness of glass fabric ply. As the proportion of glass fabric ply in the hybrid laminates increases, the impact resistance of laminates increased gradually. POLYM. COMPOS., 38:2536–2543, 2017. © 2015 Society of Plastics Engineers

Permeability and impact properties of warp-knitted spacer fabrics for protective application

An experimental investigation was carried out to study the effect of interlining material on the comfort and dynamic deformation characteristics of body armour. Suitable plies of interlining materials were selected based on the fabric comfort properties and the impact resistance specified for ballistic application. Kevlar woven fabric was used to block the projectile, and the spacer fabric was used as an interlining material to ensure wearing comfort and for imparting impact resistance. The yarn denier of the middle and bottom layers of the spacer fabrics was maintained constant, and three different deniers were used for the face layer. Three different plies of spacer fabrics were analysed by means of thermophysiological comfort properties to select the suitable interlining material for body armour. The experimental results confirm that the number of plies of spacer fabrics has significant influence on the ballistic armour characteristics than the face layer denier as proved by two-way ANOVA. The substantiated spacer fabric was used as an interlining material, and the depth and area of deformation were analysed. The research findings demonstrated that the three-plied warp-knitted polyester spacer fabric produced better results than single- and five-plied spacer fabrics. One-way ANOVA and Turkey’s HSD also confirmed the influence and interaction of different plies of spacer fabrics.

RC beams shear-strengthened with fabric-reinforced-cementitious-matrix (FRCM) composite

The interest in retrofit/rehabilitation of existing concrete structures has increased due to degradation and/or introduction of more stringent design requirements. Among the externally-bonded strengthening systems fiber-reinforced polymers is the most widely known technology. Despite its effectiveness as a material system, the presence of an organic binder has some drawbacks that could be addressed by using in its place a cementitious binder as in fabric- reinforced cementitious matrix (FRCM) systems. The pur- pose of this paper is to evaluate the behavior of reinforced concrete (RC) beams strengthened in shear with U-wraps made of FRCM. An extensive experimental program was undertaken in order to understand and characterize this composite when used as a strengthening system. The labo- ratory results demonstrate the technical viability of FRCM for shear strengthening of RC beams. Based on the experi- mental and analytical results, FRCM increases shear strength but not proportionally to the number of fabric plies installed. On the other hand, FRCM failure modes are related with a high consistency to the amount of external reinforcement applied. Design considerations based on the algorithms proposed by ACI guidelines are also provided.

Failure analysis of tire separation in two-sized tires on Airbus planes

Abstract Two-sized radial tires from a famous brand have been installed on Airbus planes. Several times, tread throw failures have occurred with these types of tires. Laboratory observations showed that these two-sized tires feature two cut-type belt plies (belt plies with cut cord ends lined at either edge). These are the 7th and 8th belt plies and, on all failed tires, separation occurred at the cut cord ends of the 7th belt plies. Because the cut cord ends of the 7th and 8th belt plies were not chemically pre-treated after the fabric ply was cut to get belt ply strips, the adhesion strength between the rubber and the cut cord ends decreased significantly. This means that micro-cracks initiated easily around the cut cord ends of the 7th and 8th belt plies. Due to the structural effect of these two-sized tires, there was uneven wear on their treads with the third ribs having the maximum amount of remaining thickness. Uneven tread wear resulted in a higher load at the third ribs. This generated higher temperatures around the edge of the 7th belt ply at the later stages of one life cycle. The higher temperatures decreased the strength of the local rubber and sped up the rubber's aging process. The higher loads experienced around the edges of the 7th belt ply and transferred from the third rib, and the decreased mechanical properties of the rubber at that location (due to higher temperatures), ultimately sped up micro-crack formation and expansion at the cut cord ends of the 7th belt ply. This finally led to premature tire failure. The tire manufacturer is currently taking measures to modify the structure of these two-sized tires in order to avoid uneven wear and hopefully prevent such failures in the future.

Limit of adhesion coefficient measurement of a unidirectional carbon fabric

The construction of mesoscopic models of fiber washing effects during the high pressure resin transfer molding (RTM) process with thermoplastic polymers requires the knowledge of the limit of adhesion coefficients between dry and impregnated fabric reinforcement plies and the mold. To measure these coefficients, a new method is described. During RTM process, a preform is placed in the cavity. The mold is closed to reach a given cavity thickness. Therefore, the normal stress applied to the preform can be relaxed before injection. In order to comply with these RTM specificities, the limit of adhesion coefficients are measured on relaxed preforms at given thicknesses. Hence, a first set of compression tests followed by a relaxation step are performed in order to measure the normal stresses the preforms undergo. The relaxation can reduce compression normal stress by 30%. The relaxation is taken into account for the limit of adhesion calculation. Then a second setup has been built in order to measure forces during pull-out of fabric plies inserted between other plies or metallic plates. This method provides mean values of coefficients of limit of adhesion for dry and lubricated preforms and various stacking sequences. These coefficients can be refined so as to take into account the real area of the contact interface for ply/ply and ply/mold configurations. There are also useful in the forming process of dry fabrics when inter-ply sliding occurs.

An experimental study of the effect of ply orientation on ballistic impact performance of multi-ply fabric panels

This paper presents a comprehensive experimental study of the effect of ply orientation on the ballistic performance of the multi-ply fabric panels. The fabric panels used in the experiments were constructed by laying plies of plain-woven fabrics in a selection of orientations. Particular attention was paid to the stacking sequence of fabrics with different laying angles. Ballistic impact tests were carried out on such angled fabric panels. The results showed significant improvement in energy-absorbing capacity of the angled multi-ply panel over the conventional aligned panel where all fabric plies are laid in the same orientation. The impact energy absorption by these angled fabric panels showed a 14% increase over the aligned counterpart, depending on the number of the plies. Optimizing the stacking sequence of the angled plies caused a 15% increase in impact energy absorption. For the panels with a large number of plies, such as the eight-ply panels, the effective panel construction can be determined according to the performance of the sub-level ply group.

Ballistic impact behavior of the aramid and ultra-high molecular weight polyethylene composites

This paper presents the experimental study of fiber type, fabric structure, orientation of fabric plies and thickness on the ballistic impact behavior of aramid and ultra-high molecular weight polyethylene (UHMWPE) composite laminates. Aramid composite laminates are reinforced by three kinds of fabric structures and UHMWPE composite laminates are reinforced by two kinds of fabric structures. The laminates are fabricated via autoclave curing process. The ballistic behavior of composite laminates is evaluated by ballistic limit velocity, and energy absorbed at ballistic limit. Through a series of ballistic tests, it is demonstrated that unidirectional composite laminates exhibit higher ballistic limit velocity and energy absorption on unit weight basis compared to other laminates. Interesting results are shown by UD-UHMWPE-H62® and UD-UHMWPE-Endumax® fabric-reinforced laminates. Orientation of fabric plies is found to have insignificant effect on ballistic behavior irrespective of material type. A bi-linear relationship is found between the ballistic limit velocity, energy absorption and specimen thickness.

Unlocking Function of Aramid Fibers in Multilayered Ballistic Armor

Aramid fabric plies were ballistic tested using high impact 7.62 × 51 mm ammunition in two distinct conditions: (1) as a common multilayered armor system (MAS) component backing a front Al2O3-based tile, and (2) with the same plies thickness, as a single target. Single targets of the ceramic tile and the aluminum sheet (MAS third layer) were also tested. In the MAS, the aramid dissipated more than 36 pct of the impact energy during the test compared with only ~2 pct when separated from the MAS. Microscopic examination of aramid fabric revealed many ceramic fragments with a size of a few micrometers that coated surfaces of fibers. It is shown for the first time that, in addition to already reported fabric rupture, debonding, and stretching, a massive incrustation of ceramic fragments onto the fabric fibers might be responsible for the comparatively high aramid ballistic performance as the MAS component. Besides the mechanical incrustation and van der Waals forces on the harder ceramic fragments, it is proposed that short-living surface static charges generated on the aramid fibers could contribute to the capturing process.

Study on dynamic needle thread tensions in a single needle lock stitch (SNLS) sewing machine. II. Effect of sewing speed, thickness of fabric plies, thread linear density and pre-tensions of threads

This paper reports on the effect of pre-tensions on needle and bobbin threads, sewing speed, thickness of fabric plies and the linear density of the threads on the tension peaks occurring on needle thread during sewing on a single needle lock stitch machine. The needle thread tensions are measured at two locations: above the needle bar (bottom segment) and above the needle thread tensioner (top segment). A factorial design approach is used to study the four parameters. The role of bobbin tension is studied in a separate experiment, while keeping the pre-tension on the needle thread constant. The highest tension observed on the needle thread is the stitch tightening tension which is directly affected by the pre-tension set on the needle thread disc tensioner. Heavier threads develop lower tightening tension which may affect the seam balance. The thickness of fabric plies does not affect the needle thread tension. Sewing speed has marginal influence on the stitch tightening tension near the needle thread tensioner. The pre-tension on the bobbin thread affects only the needle thread tension when the take up lever pulls up the needle thread loop to release it from the rotary shuttle hook gib.

Investigation on Vibration Behaviour of Cantilever Type Glass/Carbon Hybrid Composite Beams at Higher Frequency Range Using Finite Element Method

Woven fabric composites are now being increasingly used in aircraft and automobile structures due to balanced properties in the fabric plane. In the present work, woven fabric glass beam is modified and strengthened by interplying high modulus carbon fabric plies for improving the strength to weight ratio and thereby to achieve better performance in various dynamic conditions. The objective of the present work is to investigate the vibration behavior of cantilever type glass/carbon hybrid composite beams subjected to higher frequency of operation using finite element method. Unit plied woven fabric glass, carbon and hybrid of glass/carbon laminates were fabricated using hand layup technique. Experimental modal analysis of unit plied composite beams was carried out by impulse excitation technique under fixed free boundary condition. Theoretical modal analysis was done by finite element method using elastic constants derived from rule of mixture equations. The experimental and theoretical frequency results were compared and analyzed for finding the degree of deviation using regression analysis. The coefficients of regression analysis were used to find effective elastic constants of composite laminates. Further these effective elastic constants were applied for modal analysis of hybrid composite beams under higher frequency range. The results of mode shape, modal frequency of hybrid beams were reported and discussed. The effect of stacking sequence and effect of beam size on vibration characteristics at higher frequency range was also discussed.

Influence of Plying Strategies and Trigger Type on Crashworthiness Properties of Carbon Fiber Laminates Cured through Autoclave Processing

A small-scale experimental test able to characterize the energy absorption of a material under compression was developed by innovatively introducing self-supporting sinusoidal shape specimens, thus avoiding the complex anti-buckling devices of classical flat specimen tests. Two carbon-fiber-reinforced polymer (CFRP) pre-preg types were tested: 12 plies of unidirectional tape or 8 plies of plain weave fabric for a laminate approximately 1.8 mm thick in both cases. Three stacking sequences were analysed, in order to identify the configuration able to maximize the specific energy absorption (SEA), i.e. the energy absorbed per unit mass of crushed structure is expressed in J/g, with the unidirectional specimen providing the best results. In order to have a controlled crush, the specimens were produced with different auto-triggering configurations. Indeed, the fibers’ continuity was interrupted in selected position and to different degrees in order to investigate the SEA of the weakened laminates. For unidirectional specimens, the SEA maximum value and behaviour over the stroke were unaffected by the trigger position. Therefore, the auto-triggering configuration was able to control the position of the initial failure of the specimen without any decrease in safety performance.

Isothermal Multisection Tooling for the Automated Preforming of Carbon Fiber Composite Structures

In order to decrease CO2 emissions caused by individual transport, fibre-reinforced composite materials are used to reduce vehicle weight and thus fuel consumption. Low productivity of current processes complicates the introduction of fibre-reinforced materials to high volume series, where weight reduction would have a large impact. This paper presents an experimental preforming environment designed to take into account diverse process requirements of different binder systems and a new tooling concept. By setting different temperature levels on the moulds in areas where the material is drawn in under the blank holders and inside the cavity, prebonding of the fabric plies can be avoided and quality of the preforms is improved. Moreover, cycle time can be reduced as no heating or cooling of the tools is necessary.

Lateral crushing of empty and polyurethane-foam filled natural flax fabric reinforced epoxy composite tubes

In this research, empty and polyurethane-foam filled natural flax fabric reinforced epoxy composite tubes were fabricated using a hand lay-up process. These circular flax/epoxy tubes were laterally crushed under quasi-static compression. The effects of tube thickness (2, 4 and 6 plies), tube inner diameter (64 and 86mm) and the foam filler on the crushing characteristics and energy absorption capacity of these tubes were investigated. The progressive crushing of these tubes were analysed from photography. In addition, the energy absorption capacities of these empty and foam filled tubes were compared with the existing circular empty and/or foam filled tubes made of metallic materials (i.e. aluminium, brass, and titanium) and synthetic fibre reinforced composites (i.e. glass and carbon). The test results indicate that under lateral compression, the foam filled flax/epoxy tubes deformed showing a capability of spreading the deformation. The use of polyurethane-foam suppressed the fibre fracturing and eventually enhanced the energy absorption of the tubes during flattening process. The foam filled tubes with more fabric plies exhibited better crashworthiness compared to the empty tubes. The comparison with the existing tubes shows that the specific energy of natural flax/epoxy tube can be designed comparable to that of conventional aluminium tube and the glass/carbon composite tube as energy absorbers. It also was found that the specific energy of the empty and foam filled flax/epoxy tubes in lateral crushing were significantly lower than those in axial crushing.