Effects of Hydrothermal Seawater Aging on the Mechanical Properties and Water Absorption of Glass/Aramid/Epoxy Hybrid Composites

With the increase in the diversity of applications, the effect of environmental conditions on the mechanical properties of polymeric composites have become more valuable due to the sensitivity of polymers to aging. In this study, an experimental investigation was carried out to study the seawater aging effect on the flexural and low-velocity impact behavior of glass/aramid/ epoxy hybrid composites. Four types of composite groups that are [G6]S, [A6]S, [G3A3]S, [A3G3]S manufactured by vacuum infusion method were immersed in seawater at 25 °C and 70°C for 1000 h. Mechanical tests were conducted under three different conditions, namely, dry, wet, re-dried. As temperature increases, the water gain ratio also increases for all composite groups. Flexural strength was significantly reduced with seawater absorption for the wet state tested groups at each temperature. The reductions in flexural strength of the re-dried test groups are less than in the wet state test samples. Charpy test results showed that as the composite groups were exposed to hydrothermal aging, the impact strength of the plain glass/ epoxy, GAG/epoxy, and AGA/epoxy hybrid composite decreased. SEM analysis showed that as temperature increases, delamination and fiber/matrix cracks also increases.

Numerical and experimental study for AM50 magnesium alloy under dynamic loads

Magnesium alloys are widely used in automotive (steering wheel frames) and aerospace due to their lightweight, ductility, energy absorption and castability properties. Finite Element Analysis and design optimisation have driven the improvement of structural crashworthiness, stiffness, strength, durability, and NVH (noise vibration, harshness) performance, making it possible to meet both the safety requirements and weight reduction targets. The accuracy of the numerical methods is strongly dependent on the accuracy of the material models and parameters employed. This paper presents the numerical Simulation of the Charpy test for AM50 magnesium alloy. This standardised high-speed impact test method measures the energy absorbed by a standard specimen while breaking under an impact load. Numerical simulations were performed using Ansys LS-Dyna explicit solver combined with a Johnson-Cook material's law. Then a sensitivity study was performed using Ansys optiSLang to identify which of the input variables (JC parameters, test specimen's dimensions) has the most influence on the output variables (contact force and absorbed energy).

Numerical and Experimental Results on Charpy Tests for Blends Polypropylene + Polyamide + Ethylene Propylene Diene Monomer (PP + PA + EPDM)

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP + PA6 + EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s and its mass of 3.219 kg and these data were also introduced in the finite element model. The proposed model takes into account the system of four balls, including support and the ring of fixing the three balls and it has a finer discretization of the impact area to highlight the mechanisms of failure and their development in time. The constitutive models for four materials (polypropylene with 1% Kritilen, two blends PP + PA6 + EPDM and a blend PA6 + EPDM) were derived from tensile tests. Running simulations for each constitutive model of material makes possible to differentiate the destruction mechanisms according to the material introduced in the simulation, including the initiation and the development of the crack(s), based on equivalent plastic strain at break (EPS) for each material. The validation of the model and the simulation results were done qualitatively, analyzing the shape of broken surfaces and comparing them to SEM images and quantitatively by comparing the impact duration, energy absorbed by the sample, the value of maximum force during impact. The duration of the destruction of the specimen is longer than the actual one, explainable by the fact that the material model does not take into account the influence of the material deformation speed in Charpy test, the model being designed with the help of tests done at 0.016 m/s (1000 mm/min) (maximum strain rate for the tensile tests). Experimental results are encouraging for recommending the blends 20% PP + 42% PA6 + 28% EPDM and 60% PA6 + 40% EPDM as materials for impact protection at low velocity (1 m/s). Simulation results are closer to the experimental ones for the more brittle tested materials (with less content of PA6 and EPDM) and more distanced for the more ductile materials (with higher content of PA6 and EPDM).

Numerical and Experimental Results on Charpy Tests for Blends Polypropylene + Polyamide + Ethylene Propylene Diene Monomer (PP+PA+EDPM)

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP+PA6+EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s and its mass of 3.219 kg and these data were also introduced in the finite element model. The proposed model take into account the system of four balls, including support and the ring of fixing the three balls and it has a finer discretization of the impact area to highlight the mechanisms of failure and their development in time. The constitutive models for four materials (polypropylene with 1% Kritilen, two blends PP+PA6+EPDM and a blend PA6+EPDM) were derived from tensile tests. Running simulations for each constitutive model of material makes possible to differentiate the destruction mechanisms according to the material introduced in the simulation, including the initiation and the development of the crack(s), based on equivalent plastic strain at break (EPS) for each material. The validation of the model and the simulation results was done qualitatively, analysing the shape of broken surfaces and comparing them to SEM images and quantitatively by comparing the impact duration, energy absorbed by the sample, the value of maximum force during impact. The duration of the destruction of the specimen is longer than the actual one, explainable by the fact that the material model does not take into account the influence of the material deformation speed in Charpy test, the model being designed with the help of tests done at 0.016 m/s (1000 mm/min) (maximum strain rate for the tensile tests). Experimental results are encouraging for recommending the blends 20% PP+42% PA6+28% EPDM and 60% PA6+ 40%EPDM as materials for impact protection at low velocity (1m/s). Simulation results are closer to the experimental ones for the more brittle tested materials (with less content of PA6 and EPDM) and more distanced for the more ductile materials (with higher content of PA6 and EPDM).

EFFECT OF HOT DIPPING ALUMINIZING ON THE TOUGHNESS OF LOW CARBON STEEL

Steel that has been aluminized said as hot dipping aluminizing has better protection against corrosion and can protect against temperatures as high as 800°C. In hot dipping aluminizing, Steel is immersed into a molten aluminium for certain dipping time. The research aims to know the effect of preheating and dipping time on the toughness of low carbon steel. The method research was started by cutting the low carbon steel plate, according to ASTM E23 (Charpy test sample) into 16 pieces samples. Then the samples were grouped into four groups. Group-1 was initial samples. The Group-2 was directly immersed into molten aluminum 700 0C, for dipping time 5 minutes. The Group-3 was preheated at 700 oC for 30 minutes and then to be aluminized (700 oC) for dipping time 5 minutes. The Group-4 was preheated at 700 oC for 30 minutes and then to be aluminized (700 oC) for dipping time 10 minutes. Finally, all groups were tested by the Charpy test at room temperature. The results show that the aluminizing increases the toughness of low carbon steel from 228.125 KJ/m2 to 312.5 KJ/m2. The preheating process before aluminizing increases sharply the toughness of low carbon steel from 228.125 KJ/m2 to 512.5 KJ/m2. The increasing dipping time from 5-minute to 10-minute increase gradually the toughness from 512.5 KJ/m2 to 556.25 KJ/m2.

Non-Destructive Evaluation of RPV Embrittlement by Means of the Thermoelectric Power Method

Nondestructive evaluation (NDE) methods are widely used for inspecting safety relevant components in nuclear reactors. Most of these NDE-methods are optimized and applied for the detection of cracks but there is still no reliable NDE method for measuring the embrittlement of RPV steels. However, since the evaluation of RPV embrittlement of so-called Surveillance specimens with the Charpy test is a destructive approach, NDE methods are highly required. Among the investigated technics are acoustic (Ultrasonic scattering), electric (resistivity, thermoelectric) and magnetic (Barkhausen Noise, Non-Linear Harmonics Analysis, Micromagnetic Multiparameter) methods. However, all the methods under investigation suffer from the fact that fracture toughness of steel depends upon several factors, especially on lattice defects such as vacancies, dissolved atoms, dislocation loops, solute clusters, precipitates and dislocations. A major obstacle to the application of NDE methods for the quantification of material embrittlement is that they may be not only sensitive to these defects but also to other factors, such as magnetic, acoustic and electrical properties, as well as to surface quality and ambient temperature, etc.). In this paper, we present results gained by the optimization and application of the thermoelectric power method (TEPM) at the Paul Scherrer Institut (PSI) in Switzerland. The TEPM uses the change of the Seebeck coefficient (K) as an indicator for the material embrittlement. A clear almost linear correlation between the shift of the Nil-Ductile-Transition-Temperature (NDTT) and the change of the K was found. Beside the TEPM and its optimization with the finite element method, we describe the influencing parameters and the potential of this promising NDE method.

Compatibilization and Characterization of Polylactide and Biopolyethylene Binary Blends by Non-Reactive and Reactive Compatibilization Approaches

In this study, different compatibilizing agents were used to analyze their influence on immiscible blends of polylactide (PLA) and biobased high-density polyethylene (bioPE) 80/20 (wt/wt). The compatibilizing agents used were polyethylene vinyl acetate (EVA) with a content of 33% of vinyl acetate, polyvinyl alcohol (PVA), and dicumyl peroxide (DPC). The influence of each compatibilizing agent on the mechanical, thermal, and microstructural properties of the PLA-bioPE blend was studied using different microscopic techniques (i.e., field emission electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy with PeakForce quantitative nanomechanical mapping (AFM-QNM)). Compatibilized PLA-bioPE blends showed an improvement in the ductile properties, with EVA being the compatibilizer that provided the highest elongation at break and the highest impact-absorbed energy (Charpy test). In addition, it was observed by means of the different microscopic techniques that the typical droplet-like structure is maintained, but the use of compatibilizers decreases the dimensions of the dispersed droplets, leading to improved interfacial adhesion, being more pronounced in the case of the EVA compatibilizer. Furthermore, the incorporation of the compatibilizers caused a very marked decrease in the crystallinity of the immiscible PLA-bioPE blend.