Visualization of chemical bonding in a silica-filled rubber nanocomposite using STEM-EELS

In nanocomposites, the adhesion between nanofillers and the polymeric matrix is key to the mechanical properties. The strength and spatial distribution of the adhesive layer around the nanofillers are important, particularly the presence of chemical bonding between the nanofillers and matrix. In this work, we studied a styrene-butadiene rubber composite filled with silica nanoparticles to visualize the spatial distribution of the adhesive layer. A silane coupling agent (SCA) was added to the nanocomposite for strong adhesion. The reaction involving the SCA on the silica surface was investigated by scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Si-L2,3 spectra of the silica-filled rubber nanocomposite without the SCA were the same around the nanofillers, whereas in the nanocomposite containing the SCA the spectra were position-dependent. The spectra were fitted with the intensity profiles of the Si-L2,3 spectra of silica and SCA by multiple linear least-squares fitting. The fitting coefficients of silica and SCA were used to map the spatial distribution of the chemical bonding between silica and rubber chains. Chemical bonding was observed around the silica nanoparticles but not in the SBR matrix region, providing direct evidence of the reinforcing mechanism in the silica-filled rubber nanocomposite.

Parametric Study on Volume Fraction of Representative Volume Element (RVE) CFRP and GFRP Towards Tensile Properties

The properties such as fibre content, orientation, dimension of constituent fibres (diameter), level of intermixing of fibres, interface bonding between fibre and matrix, and arrangement of fibres between different types of fibres, influences the mechanical properties of hybrid composite.Representative Volume Element (RVE) for each constituent CFRP and GFRP assumed isotropic behavior for carbon fibre, glass fibre and epoxy resin matrix and assumed to be perfectly bonded interface between fibre and matrix region i.e. strain compatibility at the interface. The scope of study on the micro mechanical modelling via representative volume element (RVE) is limited only to unidirectional composites.

AB0796 PSORIATIC ONYCHOPATHY: MORE THAN MEETS THE EYE

Background:Psoriatic onychopathy is an independent predictor of the onset of psoriatic arthritis (PsA). Assessment of nail disease is difficult given the limited utility of clinical assessment tools for the nail.Recently, ultrasound (US) proved to be informative in the assessment of nail involvement.Objectives:We aimed to describe morphologic ultrasonographic nail disease changes and to look for correlations between these features and the characteristics of the PsA.Methods:The study included patients who met the CASPAR criteria for PsA.An US scan of patient’s nails was performed in order to study the nail, matrix and skin thickness.Results:We included 33 patients with PsA with a mean age of 51.2±12.5 years. The mean DAPSA was 22.8±19.7 (remission:9 patients, low activity: 5 patients, moderate activity: 11 patients and high activity: 8 patients).Twenty-nine patients had a personal history of skin psoriasis, present in 64 % of the patients the day of the examination with a mean PASI of 2.76 ±3.9.Eleven patients (33.4%) presented with psoriatic onychopathy (45 fingernails) with a mean mNAPSI of 14.1± 16.The most common patterns of nail involvement were:Oil-drop patches (5 fingernails), pitting (4 fingernails), onycholysis (3 fingernails), crumbling (3 fingernails), subungual hyperkeratosis (2 fingernails), leukonychia (2 fingernails),paronychia(2 fingernails), splinter hemorrhages (1 fingernail).We scanned 330 fingernails. The US study revealed dystrophy in 75 nails (22.7%) of the nails, in 17 patients (51.5%): Undulations or pitting (n=47), followed by disappearance of the anechoic space (n=38) and anechoic ventral nail plate (n=18).The mean thickness of skin, nail plate and nail matrix region were 2.25±0.32 mm, 0.38±0.07 mm and 1.89±0.33, respectively.We found a positive correlation between nail plate thickness and both skin and nail matrix region thickness (r=0.561, p=0.001 and r=0.523, p=0.002).Skin, nail and nail matrix thickness were significantly higher in men and in smokers. Manual workers did not have greater skin, nail plate nor nail matrix thickness.There were no correlations between disease activity evaluated by the ASDAS-CRP, DAS28, PASI, ESR or by CRP and any of the US parameters.In contrast, there was a significant negative correlation between psoriatic disease duration and nail plate thickness (r=-0.372, p=0,036).Conclusion:Ultrasound offers an appropriate alternative for the evaluation of the nail unit. In our study it was able to detect subclinical involvement of the nail in 30 fingernails and in two patients.Disclosure of Interests:None declared

Research on Microscopic Properties of TiBw/TC4 Composites for Drilling Process

TiB-whisker-reinforced TiBw/TC4 composites are widely used in aviation, aerospace, automotive, and various other industries. However, the drilling force and temperature have a large effect on the drilling micromechanical properties of TiBw/TC4 composites. In order to explore the micro-mechanical properties and promote the optimization of drilling process, the representative volume elements of TiBW/TC4 composites were established in the Digimat-FE software tool to determine the micromechanical properties and failure mechanism of TiBW/TC4 composites. The results show: (1) maximum stress occurs at the whiskers, whereas the minimum stress appears within the basket matrix region of the reinforced phase. (2) When the force reached 300 N and the temperature reached 75 °C, the junction between the whiskers and the matrix firstly failed; when the force reached 525 N and the temperature reached 112 °C, the matrix began to fail; when the force reached 675 N and the temperature reached 138 °C, the whiskers failed. (3) The main reason for the failure of the junction between the matrix and the whiskers was that the shear stress exceeded the connection strength and the axial stress accelerated the failure process. Displacement and rotation of the whiskers were shown to occur at the moment of junction failure, owing to differences in the stress experienced on different sides of the material.

The Effect of Soaking on Segregation and Primary-Carbide Dissolution in Ingot-Cast Bearing Steel

In this work, segregation in the cast and hot worked structure, as well as the effects of soaking on macro and micro segregation, in hypereutectoid bearing steel produced by ingot casting were studied. Samples were selected from ingots that where either as cast or soaked for twenty hours. Two similar bearing steel grades were used for this investigation. For the as cast ingot, samples were selected from both A-segregation channel regions and the matrix region. Samples were also selected from hot-worked bars originating from ingots that had been soaked for four hours or twenty hours. Micro and macro examinations of the microstructures were conducted and compared. In addition, a segregation analysis of the substitutional solute elements was performed using EDX equipment mounted on a Scanning Electron Microscope (SEM). EMPA mapping of the composition pattern in the bulk, as well as the carbides, was conducted. Precipitation of M3C, M2C, and M6C was observed. The carbides at A-segregation channels were found to have a different morphology to those precipitated in the bulk matrix. After soaking at 1200 °C for 4 h, all the primary carbides are dissolved.

Effects of brazing parameters on the microstructure and tensile shear force of copper sheets using amorphous filler metal

In this research, the objective was to investigate and measure the microstructure, tensile shear force, and fracture surface behavior when copper sheets are brazed using Cu-Ni-Sn-P amorphous filler metal. In order to examine the microstructure and its properties, assessment of the Cu-Ni-Sn-P/copper brazed joints was conducted after furnace brazing under an argon atmosphere using specific parameters relating to temperature, holding time, and loading pressure. In order to assess the tensile shear force, tensile testing was carried out. All the joints exhibited sound bonding without voids or cracks, when brazing temperatures reached 680 °C, this resulted in a maximum value for tensile shear force of 696.325 N. The microstructure consisted of both Cu-rich solid solution and a (Cu, Ni)3P phase as a eutectic structure formed in the brazing joint, and then the Cu-rich solid solution was produced as a matrix region around the eutectic structure. Fracture analysis was conducted for brazed joints which showed the ductile fractures after the shear test.

Growth and Interaction of Debonds in Local Clusters of Fibers in Unidirectional Composites during Transverse Loading

Fiber/matrix debonding in transverse tensile loading of a unidirectional composite is analyzed calculating energy release rate (ERR) for interface crack propagation. Non-uniform fiber distribution (local hexagonal fiber clustering) is assumed in the model. The matrix region containing the central fiber with the debond and the 6 surrounding fibers is embedded in a large block of homogenized composite which has the same fiber content as the region analyzed explicitly. Some of the fibers surrounding the central fiber may also have a debond. The effect of the local clustering and of the presence of other debonds on magnification of the ERR is analyzed.

Evaluation of a proposed model for concrete at mesoscopic scale

This work deals with numerical modeling of mechanical behavior in quasi-brittle materials, such as concrete. For this propose, a two-dimensional meso-scale model based on RVE existence is presented. The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions - each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and non-symmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. Our main goal here is to show a computational homogenization-based approach as an alternative to complex macroscopic constitutive models for the mechanical behavior of the brittle materials using a finite element procedure within a purely kinematical multi-scale framework. Besides, the fundamental importance of the representing dissipative phenomena in the interface zone to model the complex microstructural responses of materials like concrete is focused in this work. A set of numerical examples, involving the microcracking processes, is provided in order to illustrate the performance of the proposed modeling.

Influence of Silicon on Performance of Al/SiC Composites

Silicon is an important alloying element in Al alloys because the presence of Si improves the hardening strength of Al alloy and improves the wetting between the matrix and the reinforcement. In the present study, Al/SiC bonded specimens were fabricated by means of different temperatures and holding times. The microstructure of the composite was examined by scanning electron microscope. The concentration of Si elements at the interface region was observed by EDS techniques and diffusion of the Si elements in the matrix region was calculated by the Arrhenius equation. The hardness test was performed at the interface region. The results revealed that processing temperatures and holding times influences the concentration of Si and the hardness values near the interface region. Keywords: Al/SiC Interface bonding; SEM; EDS analysis; Micro hardness