Mechanical and tribological properties of a sintered glass-ceramic compared to granite and porcelainized stoneware

Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 degrees C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile. (C) 2011 Elsevier B.V. All rights reserved.

Influence of EVA and acrylate polymers on some mechanical properties of cementitious repair mortars

In repair works of reinforced concrete, patch repairs tend to crack in the interfacial zone between the mortar and the old concrete. This occurs basically due to the high degree of restriction that acts on a patch repair. For this reason, the technology of patch repair needs to be the subject of a discussion involving professionals who work with projects, construction maintenance and mix proportioning of repair mortars. In the present work, a study is presented on the benefits that the ethylene vinyl acetate copolymer (EVA) and acrylate polymers can provide in the mix proportioning of a repair mortar with respect to compressive, tensile and direct-shear bond strength. The results indicated that the increase in bond strength and the reduction in the influence of the deficiency in Curing conditioning are the main contributions offered by the polymers studied here. (C) 2009 Elsevier, Ltd. All rights reserved.

A critical reassessment of elastic unloading in sharp instrumented indentation experiments and the extraction of mechanical properties

This work examines the extraction of mechanical properties from instrumented indentation P-h(s) curves via extensive three-dimensional finite element analyses for pyramidal tips in a wide range of solids under frictional and frictionless contact conditions. Since the topography of the imprint changes with the level of pile-up or sink-in, a relationship is identified between correction factor beta in the elastic equation for the unloading indentation stage and the amount of surface deformation effects. It is shown that the presumption of a constant beta significantly affects mechanical property extractions. Consequently, a new best-fit function is found for the correlation between penetration depth ratios h(e)/h(max), h(r)/h(max) and n, circumventing the need for the assumption of a constant value for beta, made in our prior investigation [Acta Mater. 53 (2005) pp. 3545-3561]. Simulations under frictional contact conditions provide sensible boundaries for the influence of friction on both h(e)/h(max) and h(r)/h(max). Friction is essentially found to induce an overestimation in the inferred n. Instrumented indentation experiments are also performed in three archetypal metallic materials exhibiting distinctly different contact responses. Mechanical property extractions are finally demonstrated in each of these materials.

Medium carbon steel deep drawing: A study on the evolution of mechanical properties, texture and simulations, from cold rolling to the end product

Medium carbon steels are mostly used for simple applications; nevertheless new applications have been developed for which good sheet formability is required. This class of steels has an inherent low formability. A medium carbon hot rolled SAE 1050 steel has been selected for this study. It has been cold rolled with reductions in the 7-80% range. Samples have been used to assess the cold work hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment has been performed to obtain recrystallization. The material has been characterized in the ""as received"", cold rolled and annealed conditions, using several methods: optical microscopy, X-ray diffraction (texture), Vickers hardness and tensile testing. The 50% cold rolled and recrystallized material has been further studied in terms of sheet metal formability and texture evolution during the actual stamping of a steel toecap that has been used to validate the finite element simulations. (C) 2008 Elsevier B.V. All rights reserved.

Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress (sigma(r)), the film elastic modulus (E) and the film work hardening exponent (n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of sigma(r). Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only sigma(r). The numerical analyses were also used to further understand the effect of sigma(r) on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio VIE, where Y is the yield strength of the film. In an additional analysis, four ratios (R/h(max)) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and sigma(r) on the indentation load-displacement curves. In this case, or did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by sigma(r) and n. (C) 2010 Elsevier B.V. All rights reserved.

Mechanical properties, drying and autogenous shrinkage of blast furnace slag activated with hydrated lime and gypsum

This article reports the characteristics of blast furnace slag (BFS) pastes activated with hydrated lime (5%) and hydrated lime (2%) plus gypsum (6%) in relation to compressive strength, shrinkage (autogenous and drying) and microstructure (porosity, hydrated products). The paste mixtures were characterized using powder X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TG/DTG). BSF activated with lime and gypsum (LG) results in larger amounts of ettringite when compared with BFS activated with lime (L). Although the porosities of the L and LG mixtures were about the same, there was a greater pore refinement for the BFS activated with lime, with an increase in mesopores volume with age. The presence of ettringite and the higher volumes of macropores cause the compressive strength of BSF activated with hydrated lime plus gypsum to be smaller than that of BFS activated with lime. For both chemical activators, compressive strength developed slowly at early ages. Autogenous and drying shrinkage were greater for the BFS activated with lime, believed to result from the more refined porous structure in comparison with the mixture activated with gypsum plus lime. (c) 2010 Elsevier Ltd. All rights reserved.

Finite element analysis of mechanical properties in discontinuously reinforced metal matrix composites with ultrafine microstructure

This investigation focused on the finite element analyses of elastic and plastic properties of aluminium/alumina composite materials with ultrafine microstructure. The commonly used unit cell model was used to predict the elastic properties. By combining the unit cell model with an indentation model, coupled with experimental indentation measurements, the plastic properties of the composites and the associated strengthening mechanism within the metal matrix material were investigated. The grain size of the matrix material was found to be an important factor influencing the mechanical properties of the composites studied. (C) 1997 Elsevier Science S.A.

Effect of argon purity on mechanical properties, microstructure and fracture mode of commercially pure (cp) Ti and Ti-6Al-4V alloys for ceramometal dental prostheses

Provision of an inert gas atmosphere with high-purity argon gas is recommended for preventing titanium castings from contamination although the effects of the level of argon purity on the mechanical properties and the clinical performance of Ti castings have not yet been investigated. The purpose of this study was to evaluate the effect of argon purity on the mechanical properties and microstructure of commercially pure (cp) Ti and Ti-6Al-4V alloys. The castings were made using either high-purity and/or industrial argon gas. The ultimate tensile strength (UTS), proportional limit (PL), elongation (EL) and microhardness (VHN) at different depths were evaluated. The microstructure of the alloys was also revealed and the fracture mode was analyzed by scanning electron microscopy. The data from the mechanical tests and hardness were subjected to a two-and three-way ANOVA and Tukey`s test (alpha = 0.05). The mean values of mechanical properties were not affected by the argon gas purity. Higher UTS, PL and VHN, and lower EL were observed for Ti-6Al-4V. The microhardness was not influenced by the argon gas purity. The industrial argon gas can be used to cast cp Ti and Ti-6Al-4V.

Bis-GMA co-polymerizations: Influence on conversion, flexural properties, fracture toughness and susceptibility to ethanol degradation of experimental composites

Objectives. The aim of this study was to evaluate the influence of monomer content on fracture toughness (K(Ic)) before and after ethanol solution storage, flexural properties and degree of conversion (DC) of bisphenol A glycidyl methacrylate (Bis-GMA) co-polymers. Methods. Five formulations were tested, containing Bis-GMA (B) combined with TEGDMA (T), UDMA (U) or Bis-EMA (E), as follows (in mol%): 30B:70T; 30B:35T:35U; 30B:70U; 30B:35T:35E; 30B:70E. Bimodal filler was introduced at 80 wt%. Single-edge notched beams for fracture toughness (FT, 25 mm x 5 mm x 2.5 mm, a/w = 0.5, n = 20) and 10 mm x 2 mm x 1 mm beams for flexural strength (FS) and modulus (FM) determination (10 mm x 2 mm x 1 mm, n = 10) were built and then stored in distilled water for 24 h at 37 degrees C. All FS/FM beams and half of the FT specimens were immediately submitted to three-point bending test. The remaining FT specimens were stored in a 75%ethanol/25%water (v/v) solution for 3 months prior to testing. DC was determined with FT-Raman spectroscopy in fragments of both FT and FS/FM specimens at 24 h. Data were submitted to one-way ANOVA/Tukey test (alpha = 5%). Results. The 30B:70T composite presented the highest K(Ic) value (in MPa m(1/2)) at 24 h (1.3 +/- 0.4), statistically similar to 30B:35T:35U and 30B:70U, while 30B:70E presented the lowest value (0.5 +/- 0.1). After ethanol storage, reductions in K(Ic) ranged from 33 to 72%. The 30B:70E material presented the lowest reduction in FT and 30B:70U, the highest. DC was similar among groups (69-73%), except for 30B:70U (52 +/- 4%, p < 0.001). 30B:70U and 30B:35T:35U presented the highest FS (125 +/- 21 and 122 +/- 14 MPa, respectively), statistically different from 30B:70T or 30B:70E (92 +/- 20 and 94 +/- 16 MPa, respectively). Composites containing UDMA or Bis-EMA associated with Bis-GMA presented similar FM, statistically lower than 30B:35T:35U. Significance. Composites formulated with Bis-GMA:TEGDMA:UDMA presented the best compromise between conversion and mechanical properties. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Mechanical Testing of Indirect Composite Materials Directly Applied on Implant Abutments

Purpose: To test the strength to failure and fracture mode of three indirect composite materials directly applied onto Ti-6Al-4V implant abutments vs cemented standard porcelain-fused-to-metal (PFM) crowns. Materials and Methods: Sixty-four locking taper abutments were randomly allocated to four groups and were cleaned in ethanol in an ultrasonic bath for 5 min. After drying under ambient conditions, the abutments were grit blasted and a custom 4-cusp molar crown mold was utilized to produce identical crowns (n = 16 per group) of Tescera (Bisco), Ceramage (Shofu), and Diamond Crown (DRM) according to the manufacturer`s instructions. The porcelain-fused-to-metal crowns were fabricated by conventional means involving the construction and a wax pattern and casting of a metallic coping followed by sintering of increasing layers of porcelain. All crowns were loaded to failure by an indenter placed at one of the cusp tips at a 1 mm/min rate. Subsequently, fracture analysis was performed by means of stereomicroscopy and scanning electron microscopy. One-way ANOVA at 95% level of significance was utilized for statistical analysis. Results: The single load to failure (+/- SD) results were: Tescera (1130 +/- 239 N), Ceramage (1099 +/- 257 N), Diamond Crown (1155 +/- 284 N), and PFM (1081 +/- 243 N). Stereomicroscopy analysis showed two distinct failure modes, where the loaded cusp failed either with or without abutment/metallic coping exposure. SEM analysis of the fractures showed multiple crack propagation towards the cervical region of the crown below a region of plastic deformation at the indenter contact region. Conclusion: The three indirect composites and PFM systems fractured at loads higher than those typically associated with normal occlusal function. Although each material had a different composition and handling technique, no significant differences were found concerning their single load to fracture resistance among composite systems and PFM.

Precipitation hardening of Cu-Fe-Cr alloys - Part I - Mechanical and electrical properties

This research is part of a project whose scope was to investigate the engineering properties of new non-commercial alloy formulations based on the Cu rich corner of the Cu-Fe-Cr ternary system with the primary aim of exploring the development of a new cost-effective high-strength, high-conductivity copper alloy. The literature indicated that Cu rich Cu-Cr and Cu-Fe alloys have been thoroughly investigated. A number of commercial alloys have been developed and these are used for a variety of applications requiring combinations of high-strength, high-conductivity and resistance to softening. Little evidence was found in the literature that the Cu rich corner of the Cu-Fe-Cr system had previously been investigated for the purpose of developing high-strength, high-conductivity copper alloys resistant to softening. The aim of these present investigations was to explore the possibility that new alloys could be developed that combined the properties of both sets of alloys, ie large precipitation hardening response combined with the ability to stabilise cold worked microstructures to high temperatures while at the same maintain high electrical conductivity. To assess the feasibility of this goal the following alloys were chosen for investigation: Cu-0.7wt%Cr-0.3wt%Fe, Cu-0.7wt%Cr-0.8wt%Fe, Cu-0.7wt%Cr-2.0wt%Fe. This paper reports on the mechanical property investigation which indicated that the Cu-0.7wt%Cr-0.3wt%Fe, and Cu-0.7wt%Cr-2.0wt%Fe alloys were worthy of further investigation. (C) 2001 Kluwer Academic Publishers.

Thermomechanical environment characterisation in injection moulding and its relation to the mechanical properties of talc-filled polypropylene

This study is focused on the establishment of relationships between the injection moulding processing conditions, the applied thermomechanical environment (TME) and the tensile properties of talc-filled polypropylene,adopting a new extended concept of thermomechanical indices (TMI). In this approach, TMI are calculated from computational simulations of the moulding process that characterise the TME during processing, which are then related to the mechanical properties of the mouldings. In this study, this concept is extended to both the filling and the packing phases, with new TMI defined related to the morphology developed during these phases. A design of experiments approach based on Taguchi orthogonal arrays was adopted to vary the injection moulding parameters (injection flow rate, injection temperature, mould wall temperature and holding pressure), and thus, the TME. Results from analysis of variance for injection-moulded tensile specimens have shown that among the considered processing conditions, the flow rate is the most significant parameter for the Young’s modulus; the flow rate and melt temperature are the most significant for the strain at break; and the holding pressure and flow rate are the most significant for the stress at yield. The yield stress and Young’s modulus were found to be governed mostly by the thermostress index (TSI, related to the orientation of the skin layer), whilst the strain at break depends on both the TSI and the cooling index (CI, associated to the crystallinity degree of the core region). The proposed TMI approach provides predictive capabilities of the mechanical response of injection-moulded components, which is a valuable input during their design stage.

Re-use assessment of thermoset composite wastes as aggregate and filler replacement for concrete-polymer composite materials: a case study regarding GFRP pultrusion wastes

Glass fibre-reinforced plastics (GFRP), nowadays commonly used in the construction, transportation and automobile sectors, have been considered inherently difficult to recycle due to both the cross-linked nature of thermoset resins, which cannot be remoulded, and the complex composition of the composite itself, which includes glass fibres, polymer matrix and different types of inorganic fillers. Hence, to date, most of the thermoset based GFRP waste is being incinerated or landfilled leading to negative environmental impacts and additional costs to producers and suppliers. With an increasing awareness of environmental matters and the subsequent desire to save resources, recycling would convert an expensive waste disposal into a profitable reusable material. In this study, the effect of the incorporation of mechanically recycled GFRP pultrusion wastes on flexural and compressive behaviour of polyester polymer mortars (PM) was assessed. For this purpose, different contents of GFRP recyclates (0%, 4%, 8% and 12%, w/w), with distinct size grades (coarse fibrous mixture and fine powdered mixture), were incorporated into polyester PM as sand aggregates and filler replacements. The effect of the incorporation of a silane coupling agent was also assessed. Experimental results revealed that GFRP waste filled polymer mortars show improved mechanical behaviour over unmodified polyester based mortars, thus indicating the feasibility of GFRP waste reuse as raw material in concrete-polymer composites.

Microstructure, mechanical properties and chemical degradation of brazed AISI 316 stainless steel/alumina systems

The main aims of the present study are simultaneously to relate the brazing parameters with: (i) the correspondent interfacial microstructure, (ii) the resultant mechanical properties and (iii) the electrochemical degradation behaviour of AISI 316 stainless steel/alumina brazed joints. Filler metals on such as Ag–26.5Cu–3Ti and Ag–34.5Cu–1.5Ti were used to produce the joints. Three different brazing temperatures (850, 900 and 950 °C), keeping a constant holding time of 20 min, were tested. The objective was to understand the influence of the brazing temperature on the final microstructure and properties of the joints. The mechanical properties of the metal/ceramic (M/C) joints were assessed from bond strength tests carried out using a shear solicitation loading scheme. The fracture surfaces were studied both morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques. It was found that using a Ag–26.5Cu–3Ti brazing alloy and a brazing temperature of 850 °C, produces the best results in terms of bond strength, 234 ± 18 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, the use of the Ag–34.5Cu–1.5Ti brazing alloy and a brazing temperature of 850 °C produces the best results in terms of corrosion rates (lower corrosion current density), 0.76 ± 0.21 μA cm−2. Nevertheless, the joints produced at 850 °C using a Ag–26.5Cu–3Ti brazing alloy present the best compromise between mechanical properties and degradation behaviour, 234 ± 18 MPa and 1.26 ± 0.58 μA cm−2, respectively. The role of Ti diffusion is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ag and Cu distribution along the brazed interface seem to play the most relevant role in the metal/ceramic joints electrochemical performance.

Mechanical properties of stent-graft materials

An aneurysm is a localized blood-filled dilatation of an artery whose consequences can be deadly. One of its current treatments is endovascular aneurysm repair, a minimally invasive procedure in which an endoprosthesis, called a stent-graft, is placed transluminally to prevent wall rupture. Early stent-grafts were custom designed for the patient through the assembling of off-the-shelf components by the operating surgeon. However, nowadays, stent-grafts have become a commercial product. The existing endoprostheses differ in several aspects, such as shape design and materials, but they have in common a metallic scaffold with a polymeric covering membrane. This article aims to gather relevant information for those who wish to understand the principles of stent-grafts and even to develop new devices. Hence, a stent-graft classification based on different characteristics is presented and the desired features for an ideal device are pointed out. Additionally, the materials currently in use to fabricate this type of endoprosthesis are reviewed and new materials are suggested.