Papers by Keyword: Elastic Modulus

Abstract: Due to the fact that mechanical properties in macroscale cannot respond to that of cell wall features, it has become important to investigate nanomechanical characteristics of scaffold materials and make suitable modifications if needed. Conventional methods of mechanical testing cannot characterize the spatial distribution of material, with non-uniform stiffness, at nanoscale. One of the important methods of nanoscale testing is the force mapping using the atomic force microscope. In the present study, A comprehensive approach was developed to determine and characterize surface distribution of elastic modulus for soft biomaterials at nanoscale. Elastic modulus has been determined for collagen fibers, modified with different percentage of bio-glass nonoparticles, 0%, 30% and 60%, by applying tiny forces (1 nN). The experiments are carried out in phosphate buffer saline (PBS) pH ~ 7, to mimic the physiological environment. The scanning was performed at two different spots for each sample and three different scan sizes to investigate the large scale and short scale heterogeneity, respectively. Deep-lying structures have been sensed by varying applied load (2 nN). Our results are in agreement with previous reports. The results show increasing elasticity with increase of bioglass in collagen samples. Yet adding more bioglass decreases the stiffness of collagen fibers to the point where they become difficult to handle. Samples appear to be strongly heterogeneous with increasing the scan size. The depth sensing measurements manifest higher elasticity which reflects the lower degree of freedom in the deep-lying structures.

Abstract: The elastic modulus (E_c) of concrete is usually calculated from the compressive strength (f_c) in the design of concrete structures using standard models found in the various design codes. Most of these models were fundamentally developed for concrete made with natural coarse aggregate (NCA). Concrete containing coarse recycled concrete aggregate (CRCA) is known to have inferior mechanical properties to concrete made with NCA. Accordingly, the E_c-f_c relationship of CRCA concrete differs from that of NCA concrete. Hence, a number of researchers have endeavoured to develop predictive models for concrete made with CRCAs using different software programs. In an attempt to contribute to this subject, the present study seeks to propose a new model for predicting the E_c of CRCA concrete using an empirical approach. Data obtained from the literature was used to develop the model. Validations of the model using independent data sources gave realistic predictions. The new model can be used for practical E_c prediction, design, and analysis of sustainable concrete structures made with CRCAs.

Abstract: Modulus of Elasticity (Ec’) is a key parameter in structural engineering concrete designs. In concrete as a composite material, Ec’ is a function of compressive strength and the proportions of components in the concrete matrix (percentages of aggregates and cement). The inaccuracy and dispersity in estimating Ec’ from models provided by the existing codes of practice strongly affect the performance and design of the concrete structures. In this study, a dataset of 189 experimental concrete compressive strength results were collected from the available literature. The data set includes curing time (in days) for the concrete specimens, concrete density, experimental compressive strength (fc’), experimental Ec’ and several additives (e.g., slag, gypsum…etc.) with a total of 13 variables. Deep artificial neural networks (DANN) were used to model and analyze the effects of these variables on Ec’. A grid search over 2 hidden layers of DANNs was conducted to compute the best performed DANN. A total of 49 DANN models were developed in this study to predict concrete Ec’. The best performed DANN had a coefficient of determination (R²) of 0.81 and was selected for further analysis. Importance scoring was performed on the best DANN and results revealed that compressive strength had the highest importance score followed by water/cement ratio (w/c). Interestingly, the specimen sizes and curing days had the 6th and 8th scoring respectively from the 13 investigated variables. Ground pumice had the highest scoring compared to other additives. Sensitivity analyses were conducted revealing that at low specimen sizes of 10 mm, the Ec’ may vary by ~50%, while at higher size (150 mm), the Ec’ had less scatter and more reliable values.

Abstract: Fiber reinforced polymer materials have been used as the alternative to conventional steel reinforcement within the construction industry. While Basalt fiber reinforced polymers (BFRP) have shown improved mechanical properties and durability performance compared to conventional steel, it is not immune to degradation and corrosion when subjected to harsh environments. As such, significant studies have been conducted to simulate the mechanical properties of BFRP bars under degradation when subject to different hostile substances. However, there is no standardized conclusion for the performance of BFRP under an acidic environment and in-depth microstructure evaluation as the degradation of BFRP is influenced by myriad factors. This study aimed to produce a Response Surface Methodology (RSM) model to study the effect of pH, temperature, and immersion time on the tensile strength and elastic modulus. Data from existing literature involving acid emersion of BFRP were collected and modelled using RSM to present an overview of the degradation behavior of BFRP. In addition, a synthesis of the microstructure of BFRP reinforcing bars exposed to the acidic environment was evaluated by referring to SEM and EDX. It was concluded that the tensile strength loss due to corrosion was affected by temperature and immersion time in a linear function. On the other hand, tensile strength drop occurred exponentially as an acid with higher pH was used. Hence, the paper revealed the influence of various factors on the corrosion rate of the BFRP rebar.

Abstract: The present research shows the possibility of using an ytterbium nanosecond pulsed fiber laser for wear resistance improvement of carbon and alloy steels. The wear test was performed in accordance with the block-on-ring scheme with dry sliding friction on a friction machine. Surface dispersing/alloying was carried out from a boron carbide paste. This leads to a significant wear resistance improvement of steels. It was revealed that the mass loss during wear test reduced by several times after laser treatment compared to the non-treated samples. The wear mechanism differs depending on the type of steel and largely refers to their microstructure and composition. The tribo-oxide layer forms during the wear test.

Abstract: The effects of rare earth element Y addition on the structure, elastic modulus and hardness of Ti₈₀Nb_20-xY_x (x =0, 1, 2) alloys were investigated experimentally. The results showed that the structure of Ti-Nb-Y ternary alloys consist of the Ti-Nb matrix and Y-rich precipitates. Increasing the Y content can significantly improve the hardness and elastic modulus decreases with of Ti-Nb-Y alloys.

Abstract: The self-compacting concrete (SCC) workability is usually ensured by the addition of superplasticizers in the mixture. The effect of some properties of superplasticizers was investigated by many researchers. However, in the literature, there is no study related to the effect of dry extract of superplasticizer admixture on the rheological and mechanical properties of self-compacting concrete.The objective of this work is to characterize the effects of six types of superplasticizers with various solids on the rheological properties as well as the compressive strength and elastic modulus of SCC.This experimental study shows that the dry extract of superplasticizer affects the various properties of concrete both in the fresh and hardened state: first, the dry extract allows controlling the flow properties (the lower its value, the more the concrete is self-compacting), and second, the dry extract allows the reduction of the water to cement ratio (the greater its value, the stronger the concrete). The statistical coefficients, analyzed in this work, indicate a high-level relationship between the dry extract and the rheological and mechanical behavior of SCC.

Abstract: In order to improve forming quality of high strength 21-6-9 tube bending and achieve its precise bending forming, the springback behaviors of high strength 21-6-9 tube in rotary draw bending are investigated. Based on explicit/implicit finite element (FE) software of ABAQUS, the whole rotary draw bending FE model of high strength 21-6-9 tube considering variation of elastic modulus was established, and its reliability was verified. Then, the springback behaviors considering varied elastic modulus of high strength 21-6-9 tube in rotary draw bending under different process parameters were explored and compared that with constant elastic modulus. The results show that the variation tendencies of springback angle are similar with or without considering varied elastic modulus, but augments the value of springback angle with considering varied elastic modulus. Springback angle augments with the increase of the friction coefficient of tube versus mandrel, the friction coefficient of tube versus wiper die or with the decrease of the friction coefficient of tube versus pressure die, while the springback angle firstly declines and then augments with increasing the clearance of tube versus pressure die and the clearance of tube versus wiper die.

Abstract: In this study we investigate the addition of short polypropylene (PP) fibers in cement mortars for a wide volume percentage range. These fibers are dispersed easily in fresh mortar and create a dense network, whereas have as result the cracking reduction during dry shrinkage and the improvement of post peak response. A modified superplasticizer by lignosulfonate polymers basis was used, that keeps at low level the water to cement ratio and thus resulting to an improved mortar’s workability. Compressive strength, three-point flexural strength, drying shrinkage of hardened mortar, flow table test and air content of fresh mortar were studied in a range of volume percentages. The experimental response according to volume percentage was approximated by suitably attached theoretical models. The comparison of the obtained experimental values was done with unreinforced specimens as reference samples. From results elaboration it is concluded that the addition of PP fibers in cementitious mortars improves mortars post-peak response but weaken their compressive and flexural strengths and worsen their workability.

Abstract: The present work investigates the use of an alumino-silicate material, the pyrophyllite as cement substitution, synthetic polypropylene fibers and binder to create an unusual ultra-performance fiber concrete; new composite, which offers a wide field of possible use in construction industry. Effect of pyrophyllite on the physical-mechanical properties is analyzed. One reference fiber concrete without pyrophyllite and three fiber concretes containing 10%, 20%, 30% of pyrophyllite were elaborated. Results show that the pyrophyllite affects the characteristics of the concrete. Indeed, in the hardened state, the density of fiber concrete decreased with pyrophyllite rate increasing. Moreover, the use of pyrophyllite slows down the hardening process of concrete, consequently producing at early ages, compressive, flexural and tensile strengths and elastic modulus of concretes approaching without exceeding those of the reference fiber concrete. The fiber concretes are also considered to be of good quality. It seems that the rate of 10 % of pyrophyllite generates the best physical-mechanical performances that approach those of the reference fiber concrete. The use of pyrophyllite as a cement substitution is beneficial since it can help to decrease the production of cement; the amount of CO₂ released and protects the environment.