The use of ground & ultrasonicated dolomite (GUD) for improving the tensile performance of Poly (ethylene-co-vinyl acetate) copolymer composite

The combination of the organic and inorganic materials to fabricate a new form of material called ‘composite’ has been performed since several decades ago. However, the strategy to improve the homogeneity of the resultant composite system is still being the main focus of current research. In this study, dolomite and poly (ethylene-co-vinyl acetate) (PEVAc) were employed as filler and matrix, respectively. Dolomite was ground and ultrasonicated before being used as filler. It can be observed that the size of dolomite particles has been reduced significantly upon the grinding and ultrasonication processes. The effect of ground and ultrasonicated dolomite (GUD) addition on the mechanical performance of the PEVAc copolymer was investigated. Results indicate that the GUD filler has successfully increased the tensile strength, elongation at break, modulus of elasticity and tensile toughness of the PEVAc copolymer when being employed in 1 wt%. However, the use of higher content of GUD resulted in the decreasing trend of those properties. This shows that the ground and ultrasonicated dolomite with smaller and higher surface area particles than its pristine form could bring improvement to the mechanical performance of the copolymer when being used in low loading as it can be more easily dispersed in the copolymer matrix.

EFFECT OF TIO2 PARTICLES ON THE MECHANICAL AND MICROSTRUCTURAL EVOLUTION OF HYBRID ALUMINUM-BASED COMPOSITES FABRICATED BY WARB

In this study, the effect of powder particle contents on the mechanical properties of aluminum-based hybrid composites produced by warm accumulative roll bonding (WARB) process was investigated. Three hybrid composite groups with fully annealed AA1060 strips, 1[Formula: see text]wt.% of MnO2 and 0, 7.5 and 15[Formula: see text]wt.% of TiO2 were first roll-bonded and then the ARB process continued up to eight rolling cycles. In the WARB process, the samples were preheated at 300∘C for 5[Formula: see text]min before each rolling cycle. It was realized that increasing the number of ARB cycles with 0 and 7.5[Formula: see text]wt.% of TiO2 particles improved the uniformity of TiO2 particles distribution in the aluminum matrix. Also, in samples with high contents of TiO2 particles (15%), TiO2 clusters converted into small clusters with a better distribution through the aluminum matrix. Also, by increasing the number of cycles and TiO2 wt.% up to 15%, the tensile strength, elongation, tensile toughness and average Vickers microhardness of hybrid composites were increased first and decreased then. Moreover, the effects of ARB cycles and TiO2[Formula: see text]wt.% on the fracture surface of hybrid composites have been studied by scanning electron microscopy (SEM). It was found that all the samples fabricated with one and two ARB cycles exhibited a typical ductile fracture containing deep dimples, whereas by increasing the TiO2[Formula: see text]wt.% and ARB cycles, a combination of ductile and shear ductile fracture have been detected in the fracture behavior.

Mechanical Behavior of Toughened Epoxy Structural Adhesives for Impact Applications

The focus of our study is to identify physical properties of different impact-resistant/toughened structural adhesives and identify/develop an elastic-viscoelastic-plastic model as a function of loading rate by using Ludwik-type equations to be able to predict adhesive behavior at higher loading rates and to make cars more crashworthy. For this purpose, we first characterized eight different commercial toughened epoxy structural adhesives to provide detailed information about their constituents using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS). Most (but not all) of the model adhesives contained organic tougheners in the form of carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, as well as polyurethane adducts. The main crystalline inorganic phases were found as calcite (CaCO3), wollastonite (CaSiO3) or calcium silicate (CaSiO3), talc (Mg3Si4O10 (OH)2), zeolite which is an alumina silicate based mineral and has many different elements in its composition (M2/nO·Al2O3·xSiO2·yH2O, M can be Mg, Na, Ca, K, Li). The total amount of inorganic fillers was found to be different in each adhesive. Material behavior of the model adhesives were determined via tensile tests and Single Lap Joint (SLJ) tests in shear. Split Hopkinson pressure bar (SHPB) was also used to measure the strain and stress values at higher strain rates in the order of 102 s−1, which is generally encountered in impact related loading situations. Toughness values in the range ~0.5 to ~1.35 MJ/m3 were observed with the model adhesives tested in tensile mode within the ~3 × 10−3 to 0.18 m/m/s strain rate range. The softening behavior of the elastic moduli at higher strain rates observed during tensile testing was also observed with SHPB testing. It is remarkable that, overall, the modulus magnitudes seem to be similar between the tensile test and SHPB specimens within this softening range of the initial bilinear elastic behavior observed. When the results from bulk (tensile) and bonded (shear) specimens were compared, it was clearly seen that the toughness responses of the adhesives to (tensile/shear) strain rates in the bulk and bonded forms, respectively, were different, with the bonded shear toughness values in the ~25 to ~120 MJ/m3 range within ~1.25 to ~25 mm/mm/s shear strain range. The model adhesive which included just inorganic fillers had the lowest tensile toughness at the lowest tensile strain rate, but the highest slope in its tensile toughness regression line, exhibited the second highest bonded shear toughness. When tested at the extension rates of 25 mm/min and 100 mm/min in bonded lap shear, the same adhesive exhibited limited interfacial failure areas, however the dominant failure mode was cohesive failure. When the extension rate increased further, transition to interfacial (adhesive) failure was observed revealing that interfacial failures do not necessarily diminish adhesive bond toughness. Our observations point to the fact that cohesive deformation/failure processes indicating interfacial separations, inter-particle interactions as well as polymer matrix deformation in high deformation loading scenario as in bonded shear loadings may provide the highest toughness. Apparently, a large inorganic filler weight fraction is not necessary to obtain high shear toughness in bonded form since the highest bonded shear toughness was obtained with the adhesive which had the least amount of inorganic fillers among the model adhesives with 14.72 wt %.

Tensile Toughness Characteristics of Cast Al-Zn-Mg Alloys Processed by Equal Channel Angular Pressing

In the current study, consequence of ECAP on the toughness characteristics of the Al-Zn-Mg alloys was studied. Three set of Al-Zn-Mg alloys (5, 10 and 15% Zn and 2% Mg) were selected and ECAPed. Also, consequence of zinc on the toughness characteristics of the alloy, before and after ECAP was studied. After ECAP, grain size of the alloys decreased and significant rise in the strength and ductility of the alloys were noticed. Mainly, modulus of toughness of the alloys increased with successive ECAP passes. But, the modulus of toughness of the alloys decreased with rise in the zinc in the material.

Comparative study of carbon-based nanofillers for improving the properties of HDPE for potential applications in food tray packaging

High-density polyethylene (HDPE)/carbon filler composites for potential applications in food tray packaging were prepared by melt compounding HDPE with one-dimensional (1D)-multiwalled carbon nanotubes (MWCNT), two-dimensional (2D)-graphene oxide (GO) and three-dimensional (3D)-carbon black (CB) on a twin-screw extruder. The morphology of fillers inside the HDPE matrix was characterized and correlated to the mechanical, thermal and barrier properties of the nanocomposites. The results showed the distinct effect of CB on the mechanical, thermal and barrier properties of HDPE from MWCNT and GO. The morphological analysis revealed uniform dispersion for all the fillers, but the agglomerate formation was a lot more evident in MWCNT-based nanocomposites. Ball milling solved the large agglomerate formation for MWCNT and produced nanocomposites with improved mechanical properties. In comparison to 1D and 2D nanofillers, the 3D-CB filler showed remarkable contribution to tensile toughness but caused a reduction in barrier properties of HDPE, the increase in tensile toughness was attributed to uniform dispersion of the filler, enhanced mechanical interlocking between filler and polymer, appearance of high degree of crazing on tested samples and increase in nanocomposite internal temperature during tensile testing.