Continuous Blown Film Preparation of High Starch Content Composite Films with High Ultraviolet Aging Resistance and Excellent Mechanical Properties

Starch/PBAT blown films with high ultraviolet aging resistance and excellent mechanical properties were prepared by introducing lignin with polyurethane prepolymer (PUP) as a starch modifier and physical compatibilizer and 4,4′–methylene diphenyl diisocyanate (MDI) as a crosslinker. Starch was modified by reacting the NCO groups of the PUP with the OH groups of the starch to form a carbamate bond. The mechanical properties, hydrophobic properties, ultraviolet barrier, ultraviolet aging properties and microscopic morphology of starch/PBAT films with different contents of lignin were investigated. The results showed that the starch/PBAT films were blown continuously. The addition of lignin did not decrease the mechanical properties. On the contrary, the film with 1% lignin possessed the excellent mechanical properties with longitudinal tensile strength of 15.87 MPa and the elongation at a break of 602.21%. In addition, the higher the lignin content, the better the UV blocking effect. The introduction of lignin did not affect the crystalline properties but improved the hydrophilic properties and sealing strength of the high starch content composite films.

Foam Polymers in Multifunctional Insulating Coatings

The application of foamed polymers as one of the components of insulating coatings allows to solve the problems of energy saving and creation of optimal operating conditions for constructions. The systems of application of energy-efficient heat-insulating materials must consider both the particularities of the insulating materials and the functional orientation of the constructions. The implementation of the concept of seamless insulating coatings implies the achievement of thermal effect and reduction in air permeability both by means of the application of thermal insulation with low thermal conductivity and the minimization of junctions between separate elements of the insulating coating, which is achieved using elastic foamed polymers and, first of all, polyethylene foam. Construction of seamless insulating coatings creates practically impermeable heat, vapor, and water barriers along the outer perimeter of the insulated object. Multilayer products based on polyethylene foam represent a relatively new material—a fact that requires examination of their properties, as well as under various operating conditions, and development of a methodology for evaluation of the operational resistance of these materials in structures of different purposes, including cold conservation. The performed tests have shown that the compressive strength at 10% deformation is determined by the function of load application area and varies from 70 kPa during the test of cube samples of 10 × 10 × 10 in size to 260 kPa for areas exceeding 100 m2. The longitudinal tensile strength amounts to 80–92 kPa, and the strength of the weld seam is equal to 29–32 kPa. It has been established that the values of thermal conductivity of polyethylene foam with an average density of 18–20 kg/m3 amounts to 0.032–0.034 W/(m·K), diffusion moisture absorption is equal to 0.44 kg/m2 without a metallized coating and 0.37 kg/m2 with a metallized coating; water absorption after partial immersion in water for 24 h amounts to 0.013 kg/m2; water absorption by volume after complete water immersion for 28 days is equal to 0.96%. The material does not practically change its properties under conditions of long-term temperature alteration from −60 to +70 °C. The developed and implemented insulation systems for protective surfaces of framed construction objects, rubbhalls and frameless structures, floating floors, indoor ice rinks, and snow conservation systems are presented.

SUB-MICROSCALE SPECKLE PATTERN CREATION ON SINGLE CARBON FIBERS FOR IN-SITU DIC EXPERIMENTS

High performance carbon and glass fibers are widely used as reinforcements in composite material systems for aerospace, automotive, and defense applications. Modifications to fiber surface treatment (sizing) is one of the ways to improve the strength of fibers and hence the overall longitudinal tensile strength of the composite. Single fiber tensile tests at the millimeter scale are typically used to characterize the effect of sizing on fiber strength. However, the characteristic length-scale governing the composite failure due to a cluster of fiber breaks is in the micro-scales. To access such micro-scale gage-lengths, we aim to employ indenters of varying radii to transversely load fibers and use scanning electron microscope (SEM) with digital image correlation (DIC) to measure strains at these lengthscales. The use of DIC technique requires creation of a uniform, random, and high contrast speckle pattern on the fiber surface such as that shown in Figure 1. In this work, we investigate the formation of sub-microscale speckle pattern on carbon fiber surface via sputter deposition and pulsed laser deposition techniques (PLD) using Gold-Palladium (Au-Pd) and Niobium-doped SrTiO3 (Nb:STO) targets respectively. Different processing conditions are investigated for both sputter deposition: sputtering current and coating duration, and PLD: number of pulses respectively to create sub-micron scale patterns viable for micro-DIC on both sized and unsized carbon fibers. By varying the deposition conditions and SEM-imaging the deposited patterns on fibers, successful pattern formation at sub-micron scale is demonstrated for both as-received sized and unsized IM7 carbon fibers of average diameter 5.2 μm via sputter deposition and PLD respectively.

OPTIMIZATION OF TAB GEOMETRY TO MINIMIZE LONGITUDINAL STRESS CONCENTRATION DURING TENSILE TESTING OF UNIDIRECTIONAL CFRP

A uniaxial tensile test is a useful method for determination of material properties, especially longitudinal tensile strength. To accurately derive the longitudinal tensile strength, it is desired that the specimen fails in in the gauge section defined here as ‘working zone’. Unidirectional (UD) composites require use of end tabs during this tensile testing to avoid damage to the specimen due to grip serrations. The grip pressure, along with sudden geometry change at the edge of end tabs leads to longitudinal stress concentrations. The conventionally used rectangular and tapered end tabs suffer from these longitudinal stress concentrations under the edge of end tabs, causing premature failure of specimen outside of the working zone. In the present paper, a simulation study is performed for comparison of conventional end tabs with hybrid specimen geometry [1] and a novel arrow-shaped end tab geometry to determine the effect of end tab geometry on longitudinal stress concentrations. The study is focused on high modulus carbon fibre HS40/epoxy UD (0°) composite. The numerical model replicates the actual set-up for uniaxial tensile testing, including contact interactions between testing machine components. The simulation results are used to further optimise the geometry and provide recommendations to eliminate or minimise longitudinal stress concentrations.

Effects of Processing Conditions and Plasticizing-Reinforcing Modification on the Crystallization and Physical Properties of PLA Films

The polylactic acid (PLA) resin Ingeo 4032D was selected as the research object. Epoxy soybean oil (ESO) and zeolite (3A molecular sieve) were used as plasticizer and reinforcing filler, respectively, for PLA blend modification. The mixture was granulated in an extruder and then blown to obtain films under different conditions to determine the optimum processing temperatures and screw rotation. Then, the thermal behaviour, crystallinity, optical transparency, micro phase structure and physical properties of the film were investigated. The results showed that with increasing zeolite content, the crystallization behaviour of PLA changed, and the haze of the film increased from 5% to 40% compared to the pure PLA film. Zeolite and ESO dispersed in the PLA matrix played a role in toughening and strengthening. The PLA/8 wt% zeolite/3 wt% ESO film had the highest longitudinal tensile strength at 77 MPa. The PLA/2 wt% zeolite/3 wt% ESO film had the highest longitudinal elongation at 13%. The physical properties depended heavily on the dispersion of zeolite and ESO in the matrix.

Evaluation of Ultimate Strength and Fundamental Frequency of Fiber/Epoxy and Fiber/Al6061 Composite Plate

Polymers and metal composites have emerged as a significant class of materials for cutting-edge engineering applications in the current material research and development environment because of their low cost, ease of design and manufacturing, and excellent and enhanced mechanical performances. The motto behind the present work is to develop a class of such materials and to study the mechanical properties of epoxy-based Glass (G/E), Graphite (Gr/E), Aramid (A/E), Carbon HM Types (C/E), and Multi-Walled Carbon Nanotube Composites (MWCNT/E) and aluminum-based MWCNT composites. An analytical solution and finite element analysis are used to evaluate and obtain the optimum mechanical properties of the lamina of the composites, such as ultimate longitudinal tensile strength, transverse tensile strength, shear strength, and the fundamental frequency of the composite plate analysis. All-side fixed boundary conditions have been used in the present study. In addition to the above, a detailed demonstrative analysis based on the after-effects of the modulus ratio and the volume fraction of the fiber on the ultimate tensile strength has also been made. In addition, the CNT AMC plate has been examined, with the findings being compared to the composite plate of Epoxy Metal Matrices (EMCs).

Dog-bone Samples may not Provide Direct Access to the Longitudinal Tensile Strength of Clear-wood

Background: Testing standards prescribe dog-bone samples for the determination of clear-wood longitudinal tensile strength. However, the literature reports a high number of invalid tests due to the unexpected failure of the sample outside the gauge length. Motivation: The paper aims at understanding the reason for the premature failure of dog-bone samples and suggesting possible strategies for improving testing protocols. Methods: The paper starts with a comparative review of standards for different orthotropic materials. Thereafter, it analyzes the stress distribution in a clear-wood dog-bone sample using a recently proposed stress-recovery procedure and Finite Elements. Finally, the sample failure is considered applying Tsai-Wu and SIA criteria. Results: Comparative review highlights the controversy on the choice of the sample geometry. Both analytical and numerical results confirm the presence of shear and transversal stresses in necking regions, overlapping with axial stress greater (up to 2%) than the one in the gauge region. As a consequence, clear-wood dog-bone samples fail not due to a pure axial stress state in the gauge region (as expected), but due to complex stress state in necking region, where failure index is 4 ~ 5% greater than the one in gauge region. Conclusion: Assuming that dog-bone samples fail in the gauge region due to pure axial stress is simplistic, as demonstrated by analytical and numerical evidence. As a consequence, interpretations of experimental results based on this belief are misleading and testing protocols should be refined. Indeed, the presence of spurious stresses interfering with expected pure axial stress seems unavoidable. Therefore, clear-wood testing standards should allow to use prismatic samples or, alternatively, to consider as valid also tests on samples breaking outside the gauge region. Both the proposed solutions apparently reduce the accuracy of the experiments, while in contrast, they provide the best achievable results, speeding up the testing procedure and reducing the testing costs.

Microstructural and Mechanical Evaluations of SAW By Manufactured Granular Basic Bonded Cr, Mo, and Cr-Mo Active Fluxes on ST37 Low Carbon Steel

Bead-on-plate submerged arc welding was conducted on St37 steel by manufactured Cr, Mo, and Cr-Mo active basic fluxes produced via the unfused bonded method. The base metal heat-affected zone and weld metal (WM) microstructures were identified and characterized by optical microscopy and scanning electron microscopy. Then, the ferrite morphologies volume fraction of WMs were measured. Moreover, the chemical analysis of slag and inclusions was evaluated by point scan energy-dispersive X-ray spectroscopy and extensively discussed. Inclusions number density and size and their effects on the formation of AF were also elaborated. Then, the WMs’ longitudinal tensile strength and Vickers hardness were measured. Finally, the Charpy V-notch test was conducted to determine the impact toughness; the fracture surfaces were investigated, as well.

Ageing effects after ozone and water immersion on tensile strength at room and high temperatures of carbon/epoxy F8552 laminates

Tensile tests were assessed to evaluate the ageing effects on carbon fiber/epoxy resin laminates exposed to ozone and water immersion. Laminates with distinct fiber arrangements (unidirectional - UD and plain weave - PW) were tested under transversal and longitudinal tensile strength at room (22°C) and high (88°C) temperatures after conditioning. The transversal tensile strength tests of UD laminates performed at room temperature show that the water immersion decreased this property in 28% when compared to non-conditioned samples. Ozone atmosphere also deteriorates the tensile strength considerably, drop of 27%. It was expected a higher drop in water immersion conditioning than in ozone atmosphere due to this conditioning attacks preferentially the external surface of specimen contrariwise the water immersion has diffusion inside the epoxy matrix. Tensile strength at high temperature shows more accentuated degradation for UD specimens exposed to water immersion (50% drop) than ozone (25%). Higher temperatures favor the degradation of the polymeric matrix and fibers/matrix interface. Tensile strength of PW laminates non-conditioned and conditioned with ozone, tested at room temperature, presented tensile strength results slightly different, 17% lower. When submitted to water immersion the results have dropped 26%, which are similar to unidirectional composite. At high temperature, PW laminate attacked with ozone had tensile strength reduced in 7%, while after water immersion the drop achieved 18%. These results show that water immersion affected the composite much more than ozone. Fractographic analyses confirmed that the combination between high temperature and conditioning promoted the degradation of matrix and fiber/matrix interface.