Linear-Nonlinear Stiffness Responses of Carbon Fiber-Reinforced Polymer Composite Materials and Structures: A Numerical Study.

The stiffness response or load-deformation/displacement behavior is the most important mechanical behavior that frequently being utilized for validation of the mathematical-physical models representing the mechanical behavior of solid objects in numerical method, compared to actual experimental data. This numerical study aims to investigate the linear-nonlinear stiffness behavior of carbon fiber-reinforced polymer (CFRP) composites at material and structural levels, and its dependency to the sets of individual/group elastic and damage model parameters. In this regard, a validated constitutive damage model, elastic-damage properties as reference data, and simulation process, that account for elastic, yielding, and damage evolution, are considered in the finite element model development process. The linear-nonlinear stiffness responses of four cases are examined, including a unidirectional CFRP composite laminate (material level) under tensile load, and also three multidirectional composite structures under flexural loads. The result indicated a direct dependency of the stiffness response at the material level to the elastic properties. However, the stiffness behavior of the composite structures depends both on the structural configuration, geometry, lay-ups as well as the mechanical properties of the CFRP composite. The value of maximum reaction force and displacement of the composite structures, as well as the nonlinear response of the structures are highly dependent not only to the mechanical properties, but also to the geometry and the configuration of the structures.

Assessment of Nano-Indentation Method in Mechanical Characterization of Heterogeneous Nanocomposite Materials Using Experimental and Computational Approaches.

This study investigates the capacity of the nano-indentation method in the mechanical characterization of a heterogeneous dental restorative nanocomposite using experimental and computational approaches. In this respect, Filtek Z350 XT was selected as a nano-particle reinforced polymer nanocomposite with a specific range of the particle size (50 nm to 4 µm), within the range of indenter contact area of the nano-indentation experiment. A Sufficient number of nano-indentation tests were performed in various locations of the nanocomposite to extract the hardness and elastic modulus properties. A hybrid computational-experimental approach was developed to examine the extracted properties by linking the internal behaviour and the global response of the nanocomposite. In the computational part, several representative models of the nanocomposite were created in a finite element environment to simulate the mechanism of elastic-plastic deformation of the nanocomposite under Berkovich indenter. Dispersed values of hardness and elastic modulus were obtained through the experiment with 26.8 and 48.5 percent average errors, respectively, in comparison to the nanocomposite properties, respectively. A disordered shape was predicted for plastic deformation of the equilateral indentation mark, representing the interaction of the particles and matrix, which caused the experiment results reflect the local behaviour of the nanocomposite instead of the real material properties.

Nano-Level Damage Characterization of Graphene/Polymer Cohesive Interface under Tensile Separation.

The mechanical behavior of graphene/polymer interfaces in the graphene-reinforced epoxy nanocomposite is one of the factors that dictates the deformation and damage response of the nanocomposites. In this study, hybrid molecular dynamic (MD) and finite element (FE) simulations of a graphene/polymer nanocomposite are developed to characterize the elastic-damage behavior of graphene/polymer interfaces under a tensile separation condition. The MD results show that the graphene/epoxy interface behaves in the form of elastic-softening exponential regressive law. The FE results verify the adequacy of the cohesive zone model in accurate prediction of the interface damage behavior. The graphene/epoxy cohesive interface is characterized by normal stiffness, tensile strength, and fracture energy of 5 × 10-8 (aPa·nm-1), 9.75 × 10-10 (nm), 2.1 × 10-10 (N·nm-1) respectively, that is followed by an exponential regressive law with the exponent, α = 7.74. It is shown that the commonly assumed bilinear softening law of the cohesive interface could lead up to 55% error in the predicted separation of the interface.

Nano modification of NZVI with an aquatic plant Azolla filiculoides to remove Pb(II) and Hg(II) from water: Aging time and mechanism study.

This paper reports the preparation and stabilization of nano zero valent iron (NZVI) on a modified aquatic plant, Azolla filiculoides, and investigates its potential for the adsorption/reduction of Pb(II) and Hg(II) ions from aqueous media even after six months of storage in the lab condition. XRD, TEM and zeta potential results demonstrated that the Azolla-NaOH could be a good stabilizer of aged NZVI (six months) and the green support suppressed the oxidation and aggregation of immobilized NZVI. Kinetic and equilibrium models for lead and mercury ions uptake were developed by considering the effect of the initial Pb(II) and Hg(II) concentrations, contact time, adsorbent dosage, initial pH and effect of temperature. The contact time to obtain equilibrium for maximum uptake by Azolla-OH-NZVI was 20min. The removal of toxic metal ions has been monitored in terms of pseudo-first- and -second-order kinetics, and the Freundlich and Langmuir isotherms models have also been utilized to the equilibrium uptake results. The uptake kinetics followed the mechanism of the pseudo-second-order equation for all systems studied, confirming chemical sorption as the rate-limiting step of adsorption mechanisms and not involving a mass transfer in solution. The thermodynamic results confirmed that the uptake of Pb(II) and Hg(II) ions were feasible, spontaneous and endothermic at 25-80°C. XRD and zeta potential data displayed the existence of Pb(0) and Hg(0) on the Azolla-OH-NZVI surface. The nanobioadsorbent revealed high recyclability due to its reasonable uptake efficiency after 7th adsorption-desorption cycles. The proposed nano biocomposite could also be utilized to uptake Pb(II) and Hg(II) ions from the real water (Anzali lagoon water). However, coated NZVI with Azolla filiculoides as a green and environmentally friendly support suppressed rapid oxidation and aggregation of the immobilized NZVI, therefore vastly enhancing the probability of environmental transport and reducing the sedimentation and potential for toxicity.

Effects of temperature change and beverage on mechanical and tribological properties of dental restorative composites.

The aim of this study was to investigate the effects of temperature change and immersion in two common beverages on the mechanical and tribological properties for three different types of dental restorative materials. Thermocycling procedure was performed for simulating temperature changes in oral conditions. Black tea and soft drink were considered for beverages. Universal composite, universal nanohybrid composite and universal nanofilled composite, were used as dental materials. The nanoindentation and nanoscratch experiments were utilized to determine the elastic modulus, hardness, plasticity index and wear resistance of the test specimens. The results showed that thermocycling and immersion in each beverage had different effects on the tested dental materials. The mechanical and tribological properties of nanohybrid composite and nanocomposite were less sensitive to temperature change and to immersion in beverages in comparison with those of the conventional dental composite.

Clinical efficacy and safety of polyethylene glycol 3350 versus liquid paraffin in the treatment of pediatric functional constipation.

BACKGROUND AND THE PURPOSE OF THE STUDY: Functional constipation is prevalent in children. Recently polyethylene glycol has been introduced as an effective and safe drug to treat chronic constipation. There are only a few clinical trials on comparison of PEG and liquid paraffin in childhood constipation. The purpose of this study was to evaluate clinical efficacy and safety of PEG 3350 solution and liquid paraffin in the treatment of children with functional constipation in Sari Toba clinic during the period of 2008-2009. METHODS: Children with a history of functional constipation were subjects of this study. One hundred and sixty children of 2-12 years old with functional constipation were randomized in two PEG and paraffin treatment groups. Patients received either 1.0-1.5 g/kg/day PEG 3350 or 1.0-1.5 ml/kg/day liquid paraffin for 4 months. Clinical efficacy was evaluated by stool and encopresis frequency/week and overall treatment success rate was compared in two groups. RESULTS AND MAJOR CONCLUSION: Compared with the baseline, defecation frequency/ week increased significantly and encopresis frequency meaningfully decreased in two groups during the period of the study. Patients using PEG 3350 had more success rate (mean: 95.3%±3.7) compared with the patients in paraffin group (mean: 87.2%±7.1) (p=0.087). Administration of PEG 3350 were associated with less adverse events than liquid paraffin. In conclusion in treatment of pediatric functional constipation, regarding clinical efficacy and safety, PEG 3350 were at least as effective as liquid paraffin and but less adverse drug events.

The changes in the transmission functioning of the ulnar nerve in a high power magnetic field.

INTRODUCTION: The present study aims at exploring the changes in the functioning of the ulnar nerve in a high power magnetic field. METHODS: 12 volunteers with a healthy peripheral nervous system participated in the study. The ulnar nerve was selected from the upper organs as the site for study. The functioning of both the sensory and motor parts of the ulnar nerve in normal conditions was electromyographically tested. Then, using the same setting, the functioning of the nerve was electromyographically tested within a high power magnetic field (0.2 Tesla). With regard to the sensory function, the distal latency and the amplitude were examined. With regard to the motor section, the duration, amplitude of the evoked potentials, and latency from two sites--distal and proximal--were examined. These results of the two readings, taken in normal condition and in a high power magnetic field, as well as the motor neural conduction velocity, were compared. RESULTS: The statistical analyses indicated that the changes in both the distal latency and amplitude of the sensory part of the ulnar nerve were significant. However, the changes in the motor function of the nerve were not significant.

Polymerization shrinkage, impact strength and roughness of montmorillonite-modified denture base resins.

Montmorillonite (MMT) was added to two commercial denture base resins, Lucitone (LU) and Accelar (AC) in amounts varying from 0-8 weight percent (wt%). The linear polymerization shrinkage, impact strength and average roughness or polishability were measured after specimens were processed using standard methods. The linear polymerization shrinkage was 1.37 and 1.02% for the unmodified denture base resins and the impact strength was 37.36 and 20.02 J/m; while the average roughness after polishing was 0.026 and 0.047 microns for LU and AC, respectively. The addition of MMT significantly (P less than 0.05) reduced the linear polymerization shrinkage and impact strength, while increasing the roughness of LU and AC.