Prediction and sensitivity analysis of CNTs-modified asphalt’s adhesion force using a radial basis neural network model

Abstract

The expected longer service life of modified asphalt can be jeopardized by different environmental factors, such as moisture, oxidation, etc. which affect the desired properties by altering the adhesive property. An insight into knowledge of the adhesive property of the asphalt can help in providing more durable asphalt pavement. The study attempted to develop different models of adhesive properties of polymers and carbon nanotubes (CNTs) modified asphalt binders. The polymer-CNT modified asphalt is processed to prepare different types of samples, by simulating the damage due to moisture and oxidization, following the corresponding standard method. An Atomic Force Microscopy (AFM) was employed to assess the nanoscale adhesion force of the tested samples following the existing functional group in asphalt. Finally, the study has developed Radial Basis Function Neural Network (RBFNN) as a function of different parameters including; asphalt chemistry (i.e. AFM tip type and constant), type and percentages of polymers and CNTs and different environmental exposures (oxidation, moisture, etc.) to predict the nano adhesion force of asphalt. It is observed that the adhesive property of the Styrene–Butadiene modified asphalt is more consistent compared to the Styrene–Butadiene–Styrene modified asphalt, while the presence of Single-Wall Nanotubes (SWNT) is observed to affect the adhesive properties of asphalt significantly as compared to Multi-Wall Nanotubes (MWNT). The higher accuracy level of RBFNN model also indicates that the functional group (tip-type) adding with the percentages and types of polymers and CNTs significantly affect the adhesive properties of asphalt.     

Stress-Induced Twinning and Phase Transformations during the Compression of a Ti-10V-3Fe-3Al Alloy

A metastable β Ti-10V-3Al-3Fe (wt pct) alloy containing different α phase fractions after thermo-mechanical processing was compressed to 0.4 strain. Detailed microstructure evaluation was carried out using high-resolution scanning transmission electron microscopy and electron back-scattering diffraction. Stress-induced β → α′′ and β → ω transformation products together with {332}〈113〉β and {112}〈111〉β twinning systems were simultaneously detected. The effects of β phase stability and strain rate on the preferential activation of these reactions were analyzed. With an increase in β phase stability, stress-induced phase transformations were restricted and {112}〈111〉β twinning was dominant. Alternatively, less stable β conditions or higher strain rates resulted in the dominance of the {332}〈113〉β twinning system and formation of secondary α′′ martensite.     

Effect of Cold Rolling on as–ECAP Interstitial Free Steel

Ti-stabilized interstitial free steel subjected to eight passes, route B_C room temperature equal channel angular pressing (ECAP) additionally was cold rolled (CR) up to 95 pct thickness reduction. Electron back-scattering diffraction and transmission electron microscopy characterized microstructural refinement and microtexture evolution, whereas the mechanical properties were assessed by uniaxial tensile tests. After 95 pct CR, the average high-angle grain boundary spacing reduces to 0.14 μm, whereas the high-angle boundary fraction increases to ~81 pct. The ECAP negative simple shear texture components rotate by ~15 deg around the transverse direction toward the rolling direction for up to 50 pct CR, with typical rolling textures observed at 95 pct CR. The decrease in boundary spacing produces a ~500 MPa gain in 0.2 pct proof stress, a ~600 MPa increase in ultimate tensile strength (UTS), and a ~4 pct loss in total elongation after 95 pct CR. Similar rates of decrease in work hardening correspond to comparable rates of cross and/or multiple slip events irrespective of the processing regime and substructural refinement. The fracture mode of the tensile samples changes from ductile to brittle type between ECAP and 95 pct CR and is attributed to the reduced work hardening capacity of the latter. The modified Hall–Petch equation shows that the convergence of high-angle boundary spacing values with their low-angle counterparts results in an increased contribution via boundary strengthening to the 0.2 pct proof stress and UTS.     

Microstructure evolution and alloying elements distribution between the phases in powder near-β titanium alloys during thermo-mechanical processing

In the present study, two powders near-β Ti alloys having a nominal composition of Ti-5Al-5Mo-5V-XCr-1Fe (X = 1–2, wt%) were studied. The alloys were produced via the blended elemental powder metallurgy technique using hydrogenated Ti powder. Microstructure evolution and the distribution of the alloying elements between the phases were investigated after each step of thermo-mechanical processing (TMP). Microstructures were refined through the TMP in both alloys. Porosity was reduced with deformation at 1173 K (900 °C) in the β phase field. The β → α phase transformation occurred during soaking at 1023 K (750 °C) in the α + β phase field. Fragmentation of the continuous grain boundary α occurred because of the 40 % deformation at 1023 K (750 °C). Variation in the concentration of the alloying elements in each phase took place through the diffusion during soaking in the α + β phase field, e.g. exit of β-stabilisers from the α-phase. However, the α phase remained supersaturated with β stabilisers. Deformation had no influence on the distribution of the alloying elements. An addition of 1 % Cr content slightly affects the amount of the α phase formed and β grain size, but it has no noticeable effect on the distribution of the alloying elements between the phases.     

EBSD Observations of Recrystallisation and Tensile Deformation in Twinning Induced Plasticity Steel

The microstructure evolution of cold-rolled and isochronally annealed Fe–24Mn–3Al–2Si–1Ni–0.06C twinning induced plasticity steel was investigated by electron back-scattering diffraction (EBSD). Deformation behaviour of a fully recrystallised sample was tracked in a selected area as a function of the true strain using a combination of interrupted tensile testing and EBSD. The results show that the cold rolled microstructure contained a large fraction of primary and secondary twins as well as remnants of annealing twins carried over from the prior hot rolling stage. A novel deconstruction technique was applied to a partially recrystallised sample in order to separate the microstructure into deformed, recovered, newly nucleated and growing recrystallised grains. The interrupted tensile tests revealed the formation of fine striations in grains with $ \langle 111\rangle $ 〈 111 〉 and $ \langle 110\rangle $ 〈 110 〉 orientations just after yielding. While the striations could be attributed to either stacking faults or the formation of fine twin packets, some of them manifested as twin boundaries as the true strain was increased up to 0.209.     

On the Degradation of Retained Austenite in Transformation Induced Plasticity Steel

Metallurgical and Materials Transactions A - A transformation-induced plasticity steel was thermomechanically processed and then transformed to bainite at an isothermal transformation temperature...     

The effect of processing parameters on the microstructure and mechanical properties of low-Si transformation-induced plasticity steels

A base low Si, high-Al transformation-induced plasticity (TRIP) steel and one with 0.03Nb and 0.02Ti (wt%) additions were subjected to thermo-mechanical processing (TMP) and galvanising simulations. The microstructure and mechanical properties were analysed using a combination of optical and electron microscopy, X-ray diffraction and tensile testing and the results compared with those from intercritically annealed–galvanised steels. The addition of Nb and Ti results in microstructure refinement and an increase in the amount of the retained austenite after TMP which in turn, leads to increases in the tensile strength (~750 MPa) and the total elongation (TE) (~29 %). A deterioration in the volume fraction of retained austenite and the mechanical properties was noted in both steels after the additional galvanising simulation. For the base steel, all TMP and galvanised samples presented with continuous yielding during tensile testing. The Nb–Ti steel exhibited discontinuous yielding and extended Lüders banding when TMP was followed by a longer coiling time. Both steels returned discontinuous yielding after the intercritical annealing–galvanising treatment. The discontinuous yielding behaviour was associated with the much finer ferrite grain size in the intercritically annealed steels and the ageing processes that take place during galvanising.