Composite Specimens Research Articles

Elevating mechanical and thermal performance on alkali‐treated pineapple/glass fibre sandwich composite

AbstractThe present work generated hybrid composite sandwiches by incorporating 65% epoxy resin and 35% reinforcements derived from pineapple and glass fibres. The specimens were subjected to mechanical characterization by tensile, flexural and impact examinations. Among the untreated samples, the specimens containing untreated pineapple fibres (PF) with a composition of 17% PF, 18% glass fibres (three layers) and 65% epoxy by weight (17PF/TLGF) showed the most superior mechanical characteristics. Nevertheless, specimens containing fibres treated with NaOH exhibited exceptional characteristics, attaining a tensile strength of 88.121 MPa, a flexural strength of 94.213 MPa and an impact energy of 4.1 J. These data indicate a 20% enhancement in both tensile and flexural strength as well as a 63% improvement in impact strength compared to specimens containing 35% PF and lacking glass fibres (35PF/0GF). In comparison to 17PF/TLGF, the specimens treated with NaOH exhibited a 4.34% gain in tensile strength, a 4.24% increase in flexural strength and a 9% increase in impact strength. Experimental TGA was performed on the chemically treated fibre composite specimens, specifically identified as 35PF/0GF and 17PF/TLGF. Approximately 260 °C marked the beginning of decomposition for the 35PF/0GF sample, but the 17PF/TLGF sample decomposed at roughly 310°C. In addition, the fragmented surface of the 17PF/TLGF sample was analysed using SEM. © 2024 Society of Chemical Industry.

Investigation of polyurea coating influence on dynamic mechanical properties of concrete

To investigate the influence of polyurea coating on the dynamic mechanical properties of concrete, this study explores the energy absorption characteristics, stress-time curves, and failure modes of polyurea-coated concrete composite specimens under dynamic loading. The variations in the dynamic mechanical properties of polyurea-coated concrete composite specimens under complex conditions, such as different polyurea coating thicknesses and locations, as well as different strengths of coated concrete, are analyzed. The results indicate that, under the same impact velocity, with the increase of polyurea coating thickness, the energy dissipation coefficient and the percentage increase in energy dissipation first gradually increase to a certain value and then decrease. Polyurea coating significantly increases the deformation capacity of concrete specimens and effectively delays the time of concrete failure. The cracks and fragments of concrete on both sides, the impact side and the back impact side, gradually decrease with the increase of polyurea coating thickness, and the impact side coated with polyurea is superior to the back impact side, but this trend becomes less significant when the coating thickness reaches around 5 mm. With the increase of concrete strength, the percentage increase in peak stress time for both the back impact side and the impact side of polyurea-coated concrete gradually decreases. Under the same impact velocity, the energy dissipation effect of polyurea-coated concrete composite specimens is superior to that of concrete specimens.The polyurea coating enhances the toughness of concrete and improves its brittleness.

Co-effects of parallel flaws and interface characteristics on the fracture behavior of rock-concrete composite specimens

The fracture behaviour of rock-concrete composite (RCC) containing interfaces and flaws is important for assessing the stability and safety of concrete systems constructed on rock foundations. Uniaxial compression experiments were performed on RCC specimens, and acoustic emission (AE) and digital image correlation (DIC) techniques were adopted to capture the characteristics of AE and crack extension process. The impacts of interface dip angle, concrete strength, and flaw geometry on the coalescence behavior of RCC specimens were analyzed. The findings indicate that four kinds of crack coalescence patterns were recognized: indirect coalescence, left-tip and right-tip cracks connected, coalescence of same-side tip cracks, and no connection. The peak strength displays a reducing trend with increasing the interface dip angle, while the peak strength presents an increasing trend with increasing concrete strength. The overlapping parallel distribution of composite specimens presents a higher peak strength. The crack coalescence mode of overlapping parallel distribution changes from the coalescence of same-side tip cracks to the no-connection mode when interface dip angle is larger. It is worth noting that cracks tend to appear first in the concrete when the strength is relatively low. The AE counts tended to increase as the interface dip angle increased, with the earliest rise in AE counts in the left-stepping distribution and longer duration in the overlapping parallel distribution. Additionally, the energy characteristics of composite specimens correlate closely with the interface dip angle and flaw geometry.

Effect of symmetrical biaxial tension on the magnetic properties of the composite specimen of two steel plates with different mechanical and magnetic properties

The results of studying the behavior of the magnetic characteristics of two-layer material containing layers of annealed sheet low-carbon Steel 15 and sheet metastable austenitic 12Kh18N9Т steel, subjected to cold rolling with a compression of 50 %, under biaxial symmetric tension have been presented. Experiments on biaxial deformation were carried out on the original biaxial testing machine, allowed to determine the physical properties of materials during elastic-plastic deformation independently along two axes. It has been shown that the coercive force of the studied two-layer material vary monotonically over the entire range of elastic-plastic biaxial deformation and can be used as an informative parameter for assessing the it’s stresses and deformations.

Evaluation of mode-I delamination toughness of composites for automotive applications

Abstract With the increasing need for energy efficiency, fiber-reinforced composites are being widely used in the automotive industry. This study investigates the inter-laminar fracture behavior of fiber-reinforced composite double cantilever beam specimens considering a non-zero slope at the root. Experiments were conducted on unidirectional and cross-ply glass fiber reinforced epoxy composite specimens and the critical delamination toughness G I C has been evaluated by the proposed weighted residual equation. The proposed mathematical model requires crack length and the load versus displacement data to evaluate delamination fracture energy. This method accounts the measurement scatter and the rotation at the crack tip. For a particular specimen, the proposed model gives a unique value of critical delamination toughness value. The critical interface failure load estimates utilizing the evaluated delamination toughness agrees well with literature and in-house test results of double cantilever beam specimens.

Acoustic Emission Energy Release Rate Model for Classification of Damage Development in Large Fiber Reinforced Plastic Composite Structures

Acoustic emission identification of fracture mechanisms in composite materials is of great importance for the practical assessment of the serviceability of aerospace structures, such as unmanned aerial vehicles, rocket motors, and others. Many scientific research studies conducted in recent decades have demonstrated the unique capabilities of the Acoustic Emission (AE) method to detect and identify different failure mechanisms, including fiber breakage, matrix cracking, and delaminations in fracture tests of composite specimens. However, testing large composite structures, in many cases, can be accompanied by multiple time-overlapped fracture events activated simultaneously, resulting in considerable difficulties in the classification and assessment of combined prolonged AE signals. In this work, we propose the Energy Release Rate (ERR) model for the classification of AE activity related to fiber-reinforced plastic (FRP) composite fracture. The model identifies accurately both micro-scopic and macro-scopic fracture mechanisms in large aerospace structures having complex composition of materials. The model is practically applied using several machine learning methods and provides a simple means to identify and discriminate typical fracture mechanisms and their combinations. Specifically, we describe ERR model, the choice of most informative AE parameters, the choice of suitable machine learning classification methods, their training and testing on FRP specimens, and validating the model in practical tests of large full-size FRP composite structures.

Effect of Areca Nut Fiber and Pineapple Leaf Fibers and Polyester Composition on Mechanical Properties of Composite

The Effect of Areca Nut Fiber and Pineapple Leaf Fibers and Polyester Composition on Mechanical Properties of Composite Diva Akbar*, Dody Yulianto Mechanical Engineering Study Program, Faculty of Engineering, Islamic University of Riau Jl. Kaharuddin Nasution Km 11 No.113 Perhentian Marpoyan, Pekanbaru Telp. 0761 – 674635 Fax. (0761) 674834 Email : divaakbar@student.uir.ac.id ABSTRACT Areca nut fiber and pineapple leaf fiber are types of fiber derived from natural fibers that are interesting to research as composite reinforcing fibers because currently they are very abundantly available. This research aims to make composite boards made from areca nut fiber and pineapple leaf fiber with polyester resin metrics for mechanical strength. This research varied different mixtures starting from areca nut fiber: pineapple leaf fiber: polyester resin, namely 20%: 30%: 50%, 25%: 25%: 50%, 30%: 20%: 50% using The hand lay up method was carried out three times in making composite board specimens. The highest bending strength results in sample one with a mixture of 20% areca nut fiber, 30% pineapple leaf fiber and 50% polyester resin were 52.60 Mpa, the impact value was 0.379 Joules/mm2. This is because there is the influence of the fiber and metric mixture which causes the elasticity modulus value to increase and because there is the influence of fiber density, where the smaller the density value the greater the mechanical strength, both bending strength and impact value. This phenomenon can be seen from macro observations, namely that composite boards experience fiber pull out with a fibrous brittle fracture type.

Damage and failure assessment of banana/ramie/epoxy composites using acoustic emission monitoring

In recent years, Composite materials that include natural fibers have played a significant role in aerospace, automotive industries, and other engineering applications. Due to its enhancing properties, the usage of composites has owing to an increase in day-to-day life. This research aims to develop a sustainable alternative material pronounced for environmental sustainability for surpassing synthetic fibers. Therefore, real-time monitoring and detection of the damage mechanisms in natural fiber composites are indispensable. In this regard, the acoustic emission (AE) technique lends itself to identifying the microscopic damage mechanisms in composite materials. Compression tests were performed in banana/ramie/epoxy composite specimens, and following consequences, the AE parameters (frequency, amplitude, counts, duration, energy rise time, etc.) were recorded. The novelty of this article is to detect the damage evolution and failure mechanisms of banana/ramie/epoxy composites under quasi-static compression with AE signal analysis for the first time. Findings showed that the stacking of hybrid reinforcing banana and ramie fiber improves the stress distribution, leading to enhanced load-carrying capacity (30.56 %), energy absorption (26.78 %), and stiffness (35.24 the compressive strength reached the maximum strength of the banana/ramie/epoxy composites%).This increase represents a substantial 30 % increase in AE energy absorption prior to failure, suggesting that the composite specimens experienced significant damage or extensive failure mechanisms Further, the AE parameters also showed that the AE energy under compression is relatively low and that frequency disperses between 70 and 150 kHz.

Experimental Evaluation of Geometric and Environmental Effects on Mechanically Fastened Non-Crimp Fabric Composites.

Corresponding to marine environmental regulations is important in shipbuilding and marine industries. The application of lightweight composite materials on ships is an effective approach to reducing the emission of greenhouse gases. The mechanical fastening method is a good candidate to assemble composites and conventional metals. The joint geometric and environmental effects are two important factors in mechanically fastened ship and marine structures. In this study, we evaluated the W/D (hole diameter to width ratio) and environmental effects on the bearing strength and failure mode of a mechanically fastened non-crimp fabric (NCF) composite material. To consider the effect of joint geometry, wherein hole diameters of 5, 6, 8, and 10 mm were machined. Further, by selecting three environmental conditions (UV, saltwater and low temperature), we evaluated environmental effects on bearing strength and failure modes of NCF composite specimens. The bearing strength increased as W/D decreased, and the bearing strength of the specimen exposed to low temperature and UV environments increased, while that of the specimen exposed to saltwater remained the same. From the failure mode analysis, the specimen that was exposed to salt fog showed the same failure mode as the unaged specimen. It was observed that the changes in the transition section and new failure mode in the xenon arc and low-temperature specimens.

Damage investigation of hybrid flax-glass/epoxy composites subjected to impact fatigue under water ageing

The aim of this study is to investigate the fatigue behaviour of hybrid flax-glass/epoxy composites under repeated impact loading subsequent to water ageing. Different plates of these composite materials were fabricated using the vacuum infusion technique. Five stacking sequences were considered: [F8], [G/F3]S, [G2/F2]S, [G3/F]S, and [G8], where F and G stand for flax/epoxy and glass/epoxy plies, respectively. Water ageing was conducted by immersing the composite specimens in tap water at room temperature for various durations, and until saturation was reached. Fatigue impact tests were carried out using three impact energies: 3, 4, and 5 J. An advanced high-resolution camera was used to monitor the evolution of damage mechanisms occurring on the non-impacted surfaces, while a laser thermometer was considered to track the temperature variations within each composite specimen. The obtained results show that flax-glass hybridization reduces the mass of absorbed water in flax/epoxy composite by up to 70%. Furthermore, there is a more pronounced decrease in longitudinal modulus and maximum stress in aged composites, with reductions of up to 70% compared to unaged ones. Additionally, visible damage occurs even at low energy levels, manifesting from the initial impacts in both aged and unaged composite laminates. Moreover, a correlation between the number of impacts to failure and the cumulative energy is revealed. Ultimately, water aging reduces the strength of the studied composite laminates and their resistance to impact fatigue. Furthermore, the hybrid laminates with high proportion of flax layers are particularly susceptible to water ageing effects.

Seismic behavior of exterior joint of CFDST column to steel beam with RC slab

To investigate the seismic performance of an exterior joint connecting concrete-filled double-skin steel tubular (CFDST) column to steel beam with reinforced concrete (RC) slab, four scaled-down joint specimens were designed at a ratio of 1:2. Quasi-static tests were conducted with different axial compression ratios were performed, and the failure mode, hysteresis curve, skeleton curve, bearing capacity, energy dissipation capacity, strength and stiffness degradation, and strain analysis of the composite joint were analyzed. A finite element method (FEM) model of the joint was constructed and validated against the obtained experimental results. Additionally, a parametric study was carried out to investigate the influence of various factors, including the hollow ratio of the CFDST column, the concrete strength of the slab, the thickness of the slab, and the width-to-thickness ratio of the outer steel tube on joint. Based on experimental studies and finite element analysis (FEA), a theoretical calculation method was proposed to evaluate the flexural capacity of the composite joints. The test results showed that the composite exterior joint specimens with RC slab failed at the beam end. Typical failure phenomena of fracture at the steel beam and horizontal end plate interfaces, steel beam flange buckling, and concrete crushing at the RC slab were observed in the experiments. While the interior joint specimen experienced significant plastic deformation and buckling at the column flange. The hysteresis curve of the specimen is elliptical and full without pinching. The presence of RC slab can effectively improve the ultimate bearing capacity, initial stiffness and energy dissipation capacity of the specimen. The FEA results show that the bearing capacity of the composite joints was improved significantly with the increase of the thickness of the slab and the width-thickness ratio of the outer steel tube. The theoretical calculation results of the flexural capacity of the joint are 86 %–112 % of the results of the finite element calculation. The stability and accuracy of the calculation method are excellent and can be effectively applied to calculate the flexural capacity in CFDST composite structural systems.

Characterization of Thermal Expansion Coefficient of 3D Printing Polymeric Materials Using Fiber Bragg Grating Sensors.

This work aims at the determination of the coefficient of thermal expansion (CTE) of parts manufactured through the Fused Deposition Modeling process, employing fiber Bragg grating (FBG) sensors. Pure thermoplastic and composite specimens were built using different commercially available filament materials, including acrylonitrile butadiene styrene, polylactic acid, polyamide, polyether-block-amide (PEBA) and chopped carbon fiber-reinforced polyamide (CF-PA) composite. During the building process, the FBGs were embedded into the middle-plane of the test specimens, featuring 0° and 90° raster printing orientations. The samples were then subjected to thermal loading for measuring the thermally induced strains as a function of applied temperature and, consequently, the test samples' CTE and glass transition temperature (Tg) based on the recorded FBG wavelengths. Additionally, the integrated FBGs were used for the characterization of the residual strain magnitudes both at the end of the 3D printing process and at the end of each of the two consecutively applied thermal cycles. The results indicate that, among all tested materials, the CF-PA/0° specimens exhibited the lowest CTE value of 14 × 10-6/°C. The PEBA material was proven to have the most isotropic thermal response for both examined raster orientations, 0° and 90°, with CTE values of 117 × 10-6/°C and 108 × 10-6/°C, respectively, while similar residual strains were also calculated in both printing orientations. It is presented that the followed FBG-based methodology is proven to be an excellent alternative experimental technique for the CTE characterization of materials used in 3D printing.

Experimental and numerical investigation of the modal parameters for thin laminated composite plates

In the present work, glass fiber-reinforced (GFR) composite specimens were fabricated using the vacuum-bag molding process. The properties related to the vibrational response of the fabricated composite plates, such as natural frequency, modal density, and damping loss factor (DLF), were investigated through both experimental and numerical approaches. The effects of different parameters, including boundary conditions (BCs), fiber orientations, laminate layer numbers, and aspect ratios, were comprehensively studied. It was found that the experimental and numerical results were in close agreement. For each case, finite element analysis was performed to determine the natural frequencies and mode shapes. Regarding the various BCs, the DLF was observed to be highest (0.47) for fully clamped BC and lowest (0.12) for free-free BC, whereas the modal density was highest (0.068) for cantilever BC and lowest (0.037) for fully clamped BC. In terms of different lamination schemes, the DLF was highest (0.42) for a plate with quasi-isotropic fibers and lowest (0.25) for a plate with unidirectional fibers, while the modal density was highest (0.068) for quasi-isotropic fibers and lowest (0.047) for unidirectional fibers. Regarding the plates with different laminate layers, the highest DLF (0.47) was observed for a plate with 16 layers, while the lowest DLF (0.33) was found in a plate with 8 layers. Conversely, the highest modal density (0.067) was observed for a plate with 8 layers, and the lowest (0.057) was noted for a plate with 16 layers. Lastly, considering aspect ratios, the highest DLF (0.48) was observed for an aspect ratio of 0.5, and the lowest (0.26) for an aspect ratio of 1.5. The highest modal density (0.09) was also observed for an aspect ratio of 0.5, while the lowest modal density (0.045) was for an aspect ratio of 1.5.

Effect of Silane-Containing Adhesives on Repair Bond Strength between Fresh and Aged Composite Materials-A Pilot Study.

This study investigated the effects of different surface treatments and a silane-containing adhesive on the repair bond strength between fresh and aged resin composites. A total of 140 composite specimens were prepared and aged for 24 h or 4 months. Each group was subdivided into seven subgroups (n = 10) depending on the surface treatment (no surface treatment (NT), sandblasting (SAND), or Sof-lex coarse disc (DISC)) in combination with the use of the silane-containing adhesive ScotchBond Universal Plus (SBU) or an adhesive without silane Prime&Bond Universal (P&B). The same composite was used for the repair as for the primary specimen. Specimens were dark stored in distilled water at 37 °C for 28 days. Shear bond strength was tested at a crosshead speed of 0.5 mm/min. The Kruskal-Wallis test with Bonferroni's post-hoc adjustment (α = 0.05) and the Mann-Whitney U-test were used for the statistical analysis. The results are shown as the median with the interquartile range. The highest bond strength (MPa) was achieved after 24 h in the DISC+P&B (20.39(16.85-28.83)). In the fresh 24 h group, the SAND+P&B (12.25(8.28-15.05)) and DISC+SBU (18.37(15.16-21.29)) were statistically similar. In the 4-month groups, both adhesives and surface treatments performed similarly. The NT, SAND, and DISC groups without adhesives had the lowest bond strength. In the repair of fresh or aged composite, the silane-containing adhesive SBU was not superior to the adhesive without the silane (P&B).

Characterization of Graphite and ZrO2 Reinforced Aluminium Metal Matrix Composite For Enhanced Mechanical Properties in Electronics Applications

Abstract The objective of this work is to examine the wear properties of a hybrid Metal Matrix Composite (MMC) consisting of 92 weight percent (wt. %) Aluminium Alloy 6061 (AA6061), 2 wt. % Graphite (C), and 6 wt. % Zirconium Dioxide (ZrO2). It was previously determined that this composition was ideal for improved metallurgical and mechanical properties. Nine specimens of the same composition were fabricated for this continuation work and put through wear tests with different applied load, sliding velocity, and sliding distance settings. To evaluate the performance of the composite, measurements were made of the wear rate and Coefficient of Friction (COF). According to the results, the wear rate typically increased as the applied load and sliding velocity increased. At the lowest load (10 N) and velocity (2 m/s), the lowest wear rate (50.90 µg) and COF (0.197) were noted. Specimens with lower wear rates had smoother surfaces and less wear, as revealed by SEM analysis of the worn surfaces; specimens with higher wear rates showed more significant surface damage, such as deeper cuts and serrations. In specimens with less wear, XRD analysis verified the presence of crystalline aluminium, indicating a strong correlation between wear resistance and the crystalline structure of the composite. Linear regression equations were created to predict wear behavior under different conditions. According to the results, the composite's wear characteristics are greatly influenced by the sliding velocity and applied load. ZrO2 and C together have lubricating and strengthening properties that, under certain circumstances, reduce wear. The composite exhibits potential for usage in electronics applications, especially in components where wear resistance and mechanical durability are critical due to its favorable wear characteristics and mechanical properties.

Assessing the Aesthetic Performance of CAD/CAM Provisional Restorative Materials: A Spectrophotometric Analysis.

Achieving color match between natural teeth and restorative materials is crucial in dentistry. Factors such as the light source, brightness, and opacity influence tooth color, determined by light absorption and scattering within the material. Advances in CAD/CAM systems have enhanced prosthodontic treatments, particularly with new temporary materials, but data on their color stability and masking ability remains limited. However, data on the color stability and masking ability of these CAD/CAM materials is limited. Telio® CAD-Temp and VITA CAD-Temp® blocks were cut into slices and polished. Composite resin specimens were prepared using a custom-designed metal resin former and light-cured. Samples were paired randomly and assigned to experimental groups based on base type and thickness (n = 30). Samples were stored in a controlled environment for 24 h before color evaluation using an EasyShade® V spectrophotometer. Color difference (ΔE) was calculated using L*, a*, and b* values. Statistical analyses included the Shapiro-Wilk test, Levene's test, and three-way ANOVA, with post-hoc comparisons using the Bonferroni method (α = 0.05). ΔE was classified according to perceptibility (PT = 1.2) and acceptability (AT = 2.7) values.

Tensile Properties of Open Hole and Unhole Sugar Palm ‘Ijuk’ (SPI) Fibre Composite Treated with Sodium Hydroxide (NaOH)

This study evaluates the effects of sodium hydroxide (NaOH) treatment on tensile properties of sugar palm 'ijuk' (SPI) fibre-reinforced polymer (FRP) composites, with and without an open hole that acts as a stress concentrator. The NaOH treatment is aimed to improve the interfacial adhesion between SPI fibres and polymer matrix. Composite specimens were prepared using the hand lay-up method, incorporating SPI fibres in various orientations, and featuring a 6 mm diameter hole. Tensile tests were conducted to evaluate the mechanical performance of SPI FRP composite, including ultimate tensile strength, Young's modulus, and elongation at break. The research also compared the properties of SPI to those of synthetic glass fibre in fibre-reinforced polymer composites. The results showed that NaOH treatment significantly improves the fibre-matrix adhesion with 26% increase in tensile strength, leading to enhanced tensile properties in both samples, regardless of hole presence. The 0° orientation provides the highest strength and stiffness when the load is applied in the direction of the fibres. While for the 90° orientation, strength reduces by 14%. The impact of the hole on stress concentration and the subsequent mechanical behaviour of the open-hole specimens is substantial. The findings of this study offer insightful perspectives on the potential use ofNaOH-treated SPI fibre in structural and other applications, demonstrating its ability to withstand tensile stresses, even with geometric discontinuities like holes.

Size effect on tensile bonding strength between new and old concrete

The interface between new and old concrete plays a significant role in reinforced concrete engineering due to its size effect and weak strength. To investigate the size effect of tensile strength in new-to-old concrete, splitting tensile tests and computed tomography (CT) scans on composite specimens were conducted. Specimen size, interface roughness, volume fraction of polyvinyl alcohol fiber and adhesive were considered. The tensile bonding strength initially increases and then decreases with interface roughness and fiber content, while size effect on the strength shows a downward trend before rising. The adhesive notably enhances the tensile bonding strength and weakens its size effect. The interface roughness, polyvinyl alcohol fibers and interface agents influence the size effect by modifying the bonding area, specimen uniformity, and characteristic structure of the interface region. At an interface roughness of 5.5 mm and a polyvinyl alcohol fiber content of 0.5 %, the maximum strength was achieved and the maximum attenuation of size effect occurred. The size effect laws of tensile bonding performance were presented based on the Weibull statistical theory, Bažant energy theory and Carpinteri multi-fractal theory. The experimental values exhibit good consistency with the predictions from the size effect models.

Deformation processes of polymer composites with stress concentrators under different reinforcement schemes

This paper is dedicated to an experimental investigation of an effect of a stress concentrator orientation on a mechanical behavior of polymer composites with various reinforcement schemes. Composite specimens have been made of layered carbon fiber reinforced polymer (CFRP) with lay-up patterns of [±45]16 and [0/90]16. The stress concentrators have been cut in a form of a rectangle (with rounded corners) orientated at angles of 0°, 45°, and 90° to a loading axis. The novel data about the composite’s mechanical behavior has been obtained by the digital image correlation (DIC) method, the acoustic emission (AE) method and the optical microscopy. Quasistatic tests have been carried out taking into account recommendations of the ASTM D5766, ASTM D3039, ASTM D3518. The effect of the stress concentrator orientation on the composite’s strength has been evaluated. It has been found that the stress concentrator does not affect the strength of the composite with the [±45]16 lay-up pattern. This peculiarity has been explained by the absence of the layers preventing the fibers system turning in the direction of the load application. The DIC method has allowed to study the evolution of inhomogeneous strain fields on the specimens’ surfaces. Computational simulations have been carried out within the elasticity stage. The results have shown that the strain fields obtained by both the DIC method and the numerical simulation were similar for the composites with the [0/90]16 reinforcement pattern. However, significant differences have been found for the [±45]16 reinforcement pattern, which have been explained by the development of inelastic zones near the stress concentrator even if the elastic stage is realized at the macrolevel. The using of the AE method and the optical microscopy has allowed to reveal typical mechanisms of the structural damage and to study their occurrence during the tests. It has been concluded that the orientation of the stress concentrator significantly influences the deformation processes of the CFRP with various reinforcement patterns.

Facile armour production from cocoon waste by a cold-pressing process

Utilising cocoon waste as reinforcement in composites offers a cost-effective alternative for soft body armour production. Cocoon waste, including damaged or uncoiled cocoons and those with pupae, is recognised as an eco-friendly choice. This study aims to develop and assess the incorporation of varying amounts of cocoon waste as reinforcement in epoxy resin matrix composites through the cold-pressing process. The cocoon waste content in the composite specimens ranged from 0 to 40 wt%. Tensile testing and ballistic impact testing were conducted to evaluate specimen performance. The cocoon waste composite plate exhibited a maximum tensile strength of 62.21 MPa at 30 wt%, slightly surpassing that of woven hemp. These findings indicate the advantageous reinforcement attributes of cocoon waste. However, a limitation was identified: bullets fully penetrated the composite plate. To address this, ultra-high-molecular-weight polyethylene was incorporated into cocoon waste composites, resulting in enhanced tensile strength (107.36 MPa) and complete bullet penetration prevention. These outcomes position the study as a promising avenue for developing body armour plates meeting the stringent level II certification standards set by the National Institute of Justice.