Papers by Keyword: Dynamic Modulus

Abstract: Dynamic modulus vs. temperature was measured in different alloys (stainless steels, Al alloys, Ti alloys, Ni-base superalloys) prepared by additive manufacturing and an anomalous trend was observed in some of them. Dynamic modulus, measured in successive mechanical spectroscopy test runs with heating-cooling cycles, exhibits an anomalous trend in the first test run that is no longer present in the successive runs. The phenomenon consists in the inversion of the decreasing trend of modulus occurring during heating and gives rise to its permanent increase at the end of the complete heating-cooling cycle. The temperature range where the modulus anomaly takes place and the permanent increase observed after cooling depend on the specific alloy. Scanning electron microscopy (SEM) observations and density measurements revealed that the irreversible process causing the anomalous behavior is the closure of pores of nanometric size leading to material densification. This result has been discussed by considering lattice diffusion.

Abstract: The Simple Performance Test (SPT) can be used to characterize the strength and load resistance of asphalt mixtures. The objectives of this study are to determine the effect of temperature on the phase angle and dynamic complex modulus of the asphalt mixtures tested at 30°C, 35°C, 40°C, 45°C and 50°C at 25Hz, 20Hz, 10Hz, 5Hz, 1Hz and 0.5Hz frequencies. The asphalt mixtures of NMAS 12.5mm are prepared using asphalt binder PEN 80/100 and PEN 60/70. The asphalt mixtures are designed using the Superpave system and compacted using the Superpave Gyratory Compactor (SGC). The dynamic modulus test results showed that at a higher temperature, the stiffness of the asphalt mixtures is affected. The dynamic modulus of the mixtures is highest at 30°C and gradually decrease at 35°C, 40°C, 45°C and 50°C respectively. The dynamic modulus values for asphalt mixtures with bitumen grade PEN 60/70 are also higher compared to the asphalt mixtures with bitumen grade PEN 80/100. Results also showed that the low phase angle values indicate low viscosity of the asphalt binder due to increase in temperature. The present study is meaningful in understanding the asphalt mixture behaviour at different temperature and loading frequencies.

Abstract: Experimental investigations on the early age, strength gain properties of fly ash blended cement concretes containing low and high volume fly ash replacement were studied. Concrete mixes were prepared with two different fly ash contents and varying concrete ingredients with water to binder ratio (w/b), fine to coarse aggregate ratio (F/c) and accelerator dosage. Five different curing techniques, namely controlled humidity curing; hot air oven curing, steam curing, hot water curing and normal water curing were adopted for curing the fly ash based concretes. Test results showed evidence the influence of accelerating admixtures and accelerated curing for obtaining the high early strength properties in fly ash mixed concrete. Most notably a maximum 1 day compressive strength of 40.20 MPa and 34.60 MPa with low (25%) and high (50%) volume fly ash concretes were obtained respectively in this study. Experimental results clearly indicated that the improvements on the strength gain properties with the careful selection of mix ingredients; accelerator addition and accelerated curing in fly ash based concrete mixes. Also, significant improvements on the flexural strength, elastic modulus, dynamic modulus and the ultrasonic pulse velocity test were noticed.

Abstract: The features of organomodifiedmontmorillonite with different concentrations of guanidine acrylate.The influence of modifiers on the relaxation properties of nanocomposites on the basis of PA6 and organoclays by dynamic mechanical analysis.

Abstract: This study demonstrates an assessment into the different effects of lime as a mineral filler for use in densely graded hot mix asphalt (HMA). Five percent by mass of hydrated lime and lime kiln dust (LKD) were added to an asphalt mixture as its mineral filler. A series of laboratory tests to evaluate stability and flow, resilient modulus and tensile stripping ratio with reference to a control mix (a commonly used HMA) were performed. The test results showed that mixing hydrated lime into a HMA mix could enhance superior performance of hydrated lime-HMA test samples for all tests, demonstrating no moisture susceptibility. Test samples of HMA with LKD also demonstrated moisture resistance and can offer a sustainable alternative to hydrated lime, yielding one quarter of the cost. The control mix proved to be an inadequate choice upon failing the stripping potential test and therefore deemed to be susceptible to moisture.

Abstract: This laboratory-based study investigated the performance characteristics of wet process crumb rubber modified asphalt (CRMA) with crumb rubber proportions between 0% and 20% by mass of the binder. This was to assess the viability of CRMA for use in countries where CRMA is not widely utilized as Australia and Thailand and primarily involved the resilient and dynamic modulus characteristics, which indicated that CRMA pavement has both positive and negative attributes. The results show that CRMA characterizes a reduced stiffness for high frequency loading, but with a greater elastic range.

Abstract: Flexible pavements deteriorate and crack with time due to the frequent traffic load imposed upon it. Many studies have been done to predict the effects of frequent traffic load and environmental conditions on pavements in the effort to find the best pavement design which resist deterioration and ensure longer pavement service time. This study investigates the effect of mixing asphalt with varying percentages of nano calcium carbonate (CaCO₃), namely 0, 2, 4, and 6 %. The mixtures were designed based on the Superpave mix design criteria. Investigation was done using several tests, namely resilient modulus, indirect tensile strength, moisture susceptibility, and dynamic modulus tests. Samples were subjected to aging to determine their resilient modulus. The results of the investigation show that resilient modulus and indirect tensile strength increased when higher percentages of nanoparticles were added to asphalt mixture, with improvement of 138 and 48.18% respectively. Modified binders showed up to 17% improvement in moisture susceptibility comparison to base asphalt mixture, while the result of dynamic modulus test showed that the stiffness of modified asphalt increased 76.69%. The investigation also found that adding 6% CaCO₃ nanoparticles to asphalt produced modified asphalt with the best performance. In addition, the results show that the modified asphalt with CaCO₃ is suitable for hot and humid regions (tropical countries) in the field of highways construction, as the modifier was able to mitigate the influences of high-temperature rutting and moisture damage.

Abstract: Precursor phenomena of melting in pure metals and alloys have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). The examined materials were the pure metals In, Sn, Pb and Bi, and some alloys of the systems In-Sn and Pb-Bi with different compositions.MS tests have been carried out by means of a novel method developed by us that permits to operate in resonance conditions and employs hollow reeds of stainless steel containing the liquid metal. In all the metals a sharp drop of dynamic modulus and a Q^-1 maximum were observed in a temperature range ΔT before melting that depends on the specific metal and its structure. Such anelastic behaviour is consistent with an increase of the interstitialcies concentration as predicted by the Granato’s theory.Moreover, HT-XRD evidenced that sudden grain re-orientation, shift and broadening of diffraction peaks occur just before the formation of the first liquid, therefore self-interstitials and vacancies seem to play a synergic role in melting. The increase of self-interstitials over ΔT has the effect of weakening interatomic bonds that favours the successive vacancy avalanche leading to the collapse of crystal lattice (melting).

Abstract: Microstructure stability of the directionally solidified Ni base IN792 superalloy has been investigated by Mechanical Spectroscopy (MS), i.e. internal friction (IF) and dynamic modulus measurements. Repeated IF test runs from room temperature to 1173 K have been carried out on the same samples and a Q^-1 maximum has been always observed above 700 K. Its position does not depend on the resonance frequency. After each run the values of modulus and Q^-1 at room temperature change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in disordered matrix which modifies dislocation density and average distance of pinning points. The results are supported by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations.

Abstract: Precursor phenomena of melting in pure metals (In, Pb, Bi and Sn) and alloys of the systems Pb-Bi and In-Sn with different compositions have been investigated by means of Mechanical Spectroscopy (MS), i.e. dynamic modulus and damping measurements. MS tests evidenced that a sharp drop of dynamic modulus E takes place in a temperature range ΔT before the formation of the first liquid: the modulus variation ΔE and the corresponding temperature range ΔT depend on the specific metal or alloy. The modulus drop is consistent with a relevant increase of interstitial concentration (self-interstitials assuming the dumbbell configuration), as predicted by the Granato’s theory of melting. The increase of damping in the same temperature range of modulus drop supports this explanation. Owing to their dumbbell configuration self-interstitials interact with the flexural vibration of samples and the periodic re-orientation under the external applied stress leads to energy loss and damping increase. The increase of self-interstitials has the effect to weaken interatomic bonds (modulus drop) and favours the collapse of crystal lattice (melting).