Different Orientation Of Fibers Research Articles

Mechanical behavior of unidirectional composites according different failure criteria

This work is about study of the mechanical behaviour of unidirectional Kevlar / Epoxy composite laminates according to different failure criteria. Varying strength parameters values, makes it possible to compare the ultimate mechanical characteristics obtained by the criteria of Tsai-Hill, Norris, Fisher, Ashkenazi and Tsai-Wu. The epoxy matrix of the material in question is reinforced with up to 60% of its volume by aramid fibers. The stack of four layers composing the arbitrarily oriented and alternating [+q/-q]S materials results in balanced symmetrical laminates. The laminate is subjected to uniaxial tensile membrane forces. Estimate of their ultimate strengths and the plotting of the failure envelope constitute the principal axis of this study. Using the theory of maximum stress, we can determine the various modes of damage of the composite. The different components of the deformation are presented for different orientations of fibers.

Multi-scale analysis of mechanical properties and damage behavior of polypropylene composite (GF50-PP) plate at room and cryogenic temperatures

In this paper, glass fiber-reinforced polypropylene (GF50-PP) composite composed of long fibers was prepared by the thermo-compression process for the very first time. This composite presents high mechanical strength and is used in infrastructures, which demand resistance against severe conditions. Mechanical strength and multi-scale damage analysis of GF50-PP composite at ambient and cryogenic temperatures have been investigated in this study using a special sampling procedure according to the microscopy observation, X-ray microtomography, ultrasonic measurement, and pyrolysis. The results demonstrated the exceptional behavior of the GF50-PP at the cryogenic temperature of −70 °C mainly due to the employment of a novel processing method (thermo-compression) for composites with long fibers, which have been previously prepared by traditional injection molding process. Tensile results presented no difference in failure strain at 20 °C and −70 °C and the fatigue lifetime for different fiber orientations was similar in 3-points bending fatigue tests for different orientations of fibers or in samples taken from different regions of the composite plate, indicating the efficinecy of this processing method. Moreover, the results of damage analysis through monotonic loading presented that by decreasing the temperature from 20 °C to −70 °C, the plasticity threshold didn’t change notably. Overall, the proposed preparation method provided outstanding uniformity and excellent mechanical properties in GF50-PP composite even at temperatures as low as −70 °C, which has not been investigated at this cryogenic temperature before.

Evaluation of the female bladder neck and urethra using MRI with fiber tractography: Prospective study on a large cohort of continent women.

To prospectively evaluate the performance of a last generation magnetic resonance imaging (MRI) device with tractography to identify the normal female urethral sphincters in terms of morphology and quantification on a large cohort of continent women. We have recorded the data of 75 continent women who underwent a diffusion tensor imaging (DTI) sequence with fiber tractography during a pelvic MR examination. Three groups of age were analyzed in terms of color fiber tracking quality and quantitative parameters (fractional anisotropy [FA] and mean diffusibility [MD]). Statistical analysis was done for the qualitative assessment using weighted kappa statistics of Cohen and for the quantitative parameters using a non-parametric Kruskal-Wallis test. For all cases, fiber-tracking resulted in a satisfactory representation of the complexity of the orientation of the fibers. The interobserver concordance of qualitative data was substantial, calculated at 0.78 (confidence interval: 0.71-0.85). For FA, there was no statistically significant difference with the age between the three urethral segments (p > 0.05). However, we registered a significant difference inside each group between the different segments (p < 0.05), corresponding to different orientation of fibers. For MD, we have found a statistically significant difference both between levels inside each group and according the age, meaning a variation of the water mobility for each type of musculature and with age (p < 0.05). DTI with fiber tractography performed on a recent MR unit is a robust method for the three-dimensional visualization of the details and connections of the urethral female sphincters. Quantitative variations with age need to be considered.

Numerical modeling of micro-friction and fiber orientation effects on the machinability of green composites

This paper aims to enhance the predictiveness of a finite element (FE) model for machining of natural fiber composites through a tribological approach based on the micro-friction phenomenon between the cutting tool and the components of the composite structure. A 2D micromechanical model for orthogonal cutting of flax fibers reinforced polylactic-acid (PLA) composites is considered in this study at different orientation of fibers. Results show that the numerical thrust forces are significantly affected by the variation of the micro-friction in the model. An optimized value of the micro-friction coefficient has been found to fit with the experimental results. The FE model provides the ability to calculate with good accuracy the effect of fiber orientation on the machinability of flax/PLA composites.

Static and fatigue characterizations of fiber glass/epoxy tubes exposed to internal pressure and/or bending moment

In this research, static and fatigue characteristics of fibrous materials is presented. The effects of fiber orientation, pressure ratio and mean stress on the fatigue characteristic of glass fiber/reinforced epoxy are investigated via testing tubular samples with different orientations of fiber [±45°]3s and [0°, 90°]3s. All samples were subjected to an internal pressure at several pressure ratios and/or a reversed bending moment. The test results indicated that, [0, 90°]3s samples had the highest bending strengths at various pressure ratios; when exposed to a minimum value of local shear stress which is zero. Pressure ratios effect is observed. It was obvious that any increase of pressure ratio had an adverse effect on samples fatigue strength for any orientation. Mean stress influence was discussed and it was stated that it had a detrimental influence on fatigue life samples with any orientation and at any pressure ratio. A new form of Goodman's equation for the present case of loading was presented and proved to be appropriate for demonstrating mean stress influence for present work.

Fabrication and characterization of cane fiber reinforced unsaturated polyester resin composites

Cane fiber of the generas Acoruscalamus, Daemonorops Draco, Daemonoropsmollis climbing palms of tropical Asia, belonging to the family palmae (palm family) and unsaturated polyester resin were used for the preparation of composites. Cane fiber was modified with 5%, 10%, 15% NaOH solution. Various physical and mechanical properties of the composite for different orientations of fiber were measured. The physical properties i.e. water absorption of treated fiber reinforced composites is lower. But the moisture content of cane fiber decreases with higher concentration of alkali solution used for treatment. The ultimate tensile strength (UTS) is higher for treated fiber reinforced composites than the raw fiber reinforced composites for any types of orientations of fibers and the tensile strain of treated fiber reinforced composites is lower than the raw fiber reinforced composites. The UTS value for treated cane fiber composites increases with increasing weight percentage of fiber than the raw fiber reinforced composite.&#x0D; Bangladesh J. Sci. Ind. Res.54(3), 247-256, 2019

Aspects regarding wearing behaviour in case of aluminium composite materials reinforced with carbon fibers

This paper presents a study regarding wear comportment of sintered composite materials obtained by mixture of aluminium with short carbon fibers. The necessity to satisfying more and more the specific functions during design of high performance structures leads to perform multi-materials such as reinforced composite parts. The wear tests were made on three different orientations of fibers on a standard machine of tribology, pin disk type. Counter-disk was made of cast iron with a superficial hardness of 92 HB. The wear rate and friction coefficient decreased exponentially with time of friction and reached a stationary value. This behaviour was attributed to the development of a lubricating film on the friction surface. To conduct this work was performed measurements on samples from the Al matrix composites and carbon fiber 43%, wear mechanism was investigated by scanning electron microscopy. In addition to fiber orientation, the tribological behaviour of metal matrix composites reinforced with fiber is influenced by the interfacial reaction of fiber-matrix. The characteristics and the dimensions of the interface depend on the cycle of temperature and time at which the material has been subjected during the manufacturing process and thereafter.

Role of different fiber orientations and thicknesses of the skins and the core on the transverse shear damping of polypropylene honeycomb sandwich structures

This paper investigates the effect of different orientations of fiber in the skins and different thicknesses of the skins and polypropylene honeycomb core (PPHC) on the transverse shear damping of the sandwich using experimental and theoretical studies. Three different sandwiches, SW1 (thickness of top and bottom FRP skin: 3.15mm each with 10mm thick PPHC), SW2 (thickness of top and bottom FRP skin: 1.575mm each with 5mm thick PPHC), SW3 (thickness of top and bottom FRP skin: 1.575mm each with 10mm thick PPHC) were fabricated for conducting experimental work. In order to study the effect of fiber orientation of the skin on the natural frequency and loss factors, five different orientations (all 0°, ±30°, ±45°, ±60° and all 90°) were considered. An impulse technique was used to calculate the natural frequency and loss factor of the composites. The natural frequency and loss factor were also computed theoretically and compared. As the in-plane load of the strong FRP skins imposes on the soft honeycomb core under dynamic condition, it causes a large transverse shear deformation on the core. This shear deformation leads to a high energy dissipation/loss factor of the sandwich. At the 0° fiber oriented sandwich, the loss factor value (η=0.0234) becomes significantly higher without losing its natural frequency (stiffness) value (fn=142.12Hz), which is not so in the case of FRP composites having the loss factor (η) value of 0.00218 and the natural frequency value (fn) of 114.23Hz. It is also found that the transverse shear effect and damping loss factor increases with the increase in the thicknesses of the skins and core of the sandwich.

Numerical analysis of effect of orientation of fibers on stress–strain response of fiber reinforced soil

The paper presents a numerical approach for incorporating the effect of orientation of fibers in the stress–strain behavior of fiber-reinforced soils. The results from the numerical analysis of stress–strain response of soil with random fiber distribution are validated with experimental results. The results show that the fibers aligned in horizontal direction in the direction of maximum extension are most beneficial. A series of numerical simulations covering different orientations of fibers have been conducted and the results are presented. The results indicate that the assumption of random fiber distribution is conservative.

Optimization of the Composite Truncated Cone Structure Layers under Buckling Load

The orientation of fibers in the layers is an important factor that must be obtained in order to predict how well the finished composite product will perform under real-world working conditions. In this research, a five-layer glass-epoxy composite truncated cone structure under buckling load was considered. The simulation of the structure was done utilizing finite element method and was confirmed comparing with the published experimental results. Then the effect of different orientation of fibers on the buckling load was considered. For this, a computer programing was developed to compute the buckling load for different orientations of fibers in each layer. These orientations were produced randomly with the delicacy of 15 degrees. Finally, neural network and genetic algorithm methods were utilized to obtain the optimum orientations of fibers in each layer using the training data obtained from finite element simulation. There are many parameters such as the number of hidden layers, the number of neurons in each hidden layer, the training algorithm, the activation function and so on which must be specified properly in development of a neural network model. The number of hidden layers and number of neurons in each layer was obtained by try and error method. In this study, multilayer back-propagation (BP) neural network with the Levenberg-Marquardt training algorithm (trainlm) was used. Finally, the results showed that the truncated cone with optimum layers withstand considerably more buckling load.

Modeling Fracture of Fiber Reinforced Polymer

In the present paper 3D rate sensitive constitutive model for modeling of laminate composites is presented. The model is formulated within the framework of continuum mechanics based on the principles of irreversible thermodynamics. The matrix (polymer) is modeled using 3D rate sensitive microplane model. For modeling of fibers (glass) a uni-axial constitutive law is employed. The fibers are assumed to be uniformly smeared-out over the matrix. The formulation is based on the assumption of strain compatibility between matrix and fibers. To account for the de-lamination of fibers, the matrix is represented by the periodically distributed bands with non-uniform strength properties over the band width. The input parameters of the model are defined by the mechanical properties of matrix and fibers (elastic properties, strength and fracture energy), the volume content of fibers and by their orientation in 3D space. The model is implemented into a 3D finite element code. To assure mesh objective results, the localization limiter is based on the assumption of constant energy dissipation within each finite element, i.e. the crack band method is used. The performance of the model is shown on one numerical example for specimens loaded in uni-axial tension. It is demonstrated that the proposed model is able to realistically predict the resistance and failure mode of complex fiber-reinforced composite for different orientation of fibers.

Modeling fracture of fiber reinforced polymer

In the present paper 3D rate sensitive constitutive model for modeling of laminate composites is presented. The model is formulated within the framework of continuum mechanics based on the principles of irreversible thermodynamics. The matrix (polyester resin) is modeled by employing a 3D rate sensitive microplane model. For modeling of fibers (glass) a uni-axial constitutive law is used. The fibers are assumed to be uniformly smeared-out over the matrix. The formulation is based on the assumption of strain compatibility between matrix and fibers. Total stress tensor is additively decomposed into the contribution of matrix and fibers, respectively. To model de-lamination of fibers, the matrix is represented by periodically distributed initial imperfection over the pre-defined bands, which are parallel to fibers. Physically, this assumption accounts for the matrix-fiber interface in a smeared way. The input parameters of the model are defined by the mechanical properties of matrix and fibers (elastic properties, strength and fracture energy), the volume fraction of fibers and by their spatial orientation. The model is implemented into a 3D finite element code. To assure mesh objective results crack band method is employed. The model is first calibrated using a few basic test results. Subsequently, the model is validated with several numerical examples for specimens loaded in uni-axial tension, uni-axial compression and shear. Comparison between numerical and test results shows that the proposed model is able to predict the resistance and failure mode of complex fiber-reinforced composite for different orientation of fibers and different loading conditions with sufficient accuracy. Finally, based on the qualitative type of the finite element analysis, it is demonstrated that the strain rate dependency becomes more important when the angle between the fiber and load direction increases.

The effects of disbonds on the pure mode II stress intensity factor of aluminium plate reinforced with bonded composite materials

Adhesively bonded composite patch repair has been widely used to restore or extend the service life of cracked structural components due to its effectiveness to mechanical repair technique. In this work, the finite element method is applied to analyse the performance of the bonded composite patch for repairing cracks emanating from semicircular notch root in pure mode II. The stress intensity factor was computed at the crack tip repaired using a boron/epoxy patch for different orientation of fibers, taking into account the disbond. In this case, the increase of a patch thickness reduces the negative effects of disbond. When this effect is significant between the patch and the plate, it reduces the repair effectiveness. The maximum reduction obtained by using a boron/epoxy of fibers in the x-direction is of the order of 20% more important compared to a patch having its fibers in the y-direction. The stress intensity factor exhibits an asymptotic behaviour as the disbond size increases.

Nondestructive Measurement of the Subsurface Structure of Biological Material Having Cellular Structure by Using Near-Infrared Spectroscopy

Biological materials–wood is a typical example–are widely used in a state where not only the cellular structure but also its bulky shape is retained. NIRS (near-infrared spectroscopy) may be called for as a promising technique to analyze the physical state of such materials as well as the chemical composition. In this report, the effects of physical conditions found in wood on the absorption of NIR radiation are examined. In the experiments, conifers (Sitka spruce) that had various degrees of surface roughness and different orientations of fibers to the direction of incident light were used. Results of these measurements showed that the orientation of fibers and the surface roughness of wood were directly related to the absorbance. In addition, it became clear that the behavior of diffusely reflected light in wood could be expressed by Kubelka–Munk theory and fell into three categories according to the characteristic of the absorption and scattering coefficient. On the basis of these results, a new concept for the behavior of NIR light passing through material made of hollow fibers has been proposed.

The dynamic mechanical method for the characterization of solid composite polymers

AbstractInformation and parameters obtainable from the dynamic mechanical thermal analysis test method are defined. The sensitivity of the technique in detecting the presence of separate phases is emphasized. The Polymer Laboratories DMTA instrumentation is briefly described and its various modes of operation, such as frequency multiplexing, discussed. The theory of the mechanical response of two phase systems is presented via the Takayanagi model approach. Series and parallel coupling constants are derived for a few systems as examples of the definition of phase morphology. Examples are given of the results for ethylene‐propylene random copolymer, block copolymer elastomers, rubber toughened poly(styrene), carbon fiber reinforced expoxies with different orientations of fiber, and carbon black filled rubbers. The engineering properties of composites are available directly from the PL‐DMTA, which provides sensitive detection of non‐linear mechanical behavior, frequently found in multi‐phase polymer systems.

Fabrication of birefringent anisotropic model materials

The discusser was interested in Prabbakaran's paper dealing with fabrication aspects of birefringent anisotropic model materials, which is brief and informative. The review of earlier investigations has brought out certain information on fabrication technology which otherwise is not explicitly available. The author cites certain interesting references of Japanese and Russian workers; however by digging deeper one may be able to see more of them.l-8 A bibliography is available elsewhere? The discusser tried a procedure very similar to that described by the author. A time-consuming procedure, a nonuniform distribution of fibers, and difficulty in providing uniform tension in fibers were the problems faced. Hence, the process was modified. The discusser used thin strands consisting of 20 to 30 filaments and used filament winding on a lathe. A thin perspex plate (30 x 30 cm) was used as a mandrel. Edges were rounded to avoid fiber breakage. The plate with fibers was soaked in resin preparation and pressed between perspex plates (no releasing agent was used for epoxy resin) to bleed out excess resin. This method yielded two models of identical properties with glossy and parallel surfaces. The method was faster , gave uniform distribution of fibers and uniform tension in fibers, and proper wetting was assured. For fabrication of a model ply with different orientation of fibers, a variation of the above method was used. The filament winding was done on a rectangular frame as mandrel. After winding was over, the filaments were transferred on to a perspex plate by pressing the plate against the fibers within the frame and bonding them to the plate edges. The subsequent layers were also transferred to the plate, but each time with different orientation of fibers. Alternatively, an octagonal plate, when used as a mandrel, gives 0-deg, 45-deg, -45-deg and 90-deg orientations. The discusser has also employed polymer fibers in plastic matrix for stress-freezing applications. A similar procedure is mentioned by Yamamoto and Yasui.3