Mechanical properties of polyamide 6 reinforced microfibrilar composites

The mechanical behavior of microfibrilar composites (MFC), consisting of a matrix of high-density polyethylene (HDPE) and reinforcement of polyamide 6 (PA6) fibrils, with and without compatibilization, was studied. The composites were produced by conventional processing techniques with various shape and arrangement of the PA6 reinforcing entities: long, unidirectional, or crossed bundles of fibrils (UDP and CPC, respectively), middle-length, randomly oriented bristles (MRB), or non-oriented micrometric PA6 spheres (NOM). The tensile, flexural, and impact properties of the MFC materials (UDP, CPC, and MRB) were determined as a function of the PA6 reinforcement shape, alignment and content, and compared with those of NOM, the non-fibrous composite. It was concluded that the in-situ MFC materials based on HDPE/PA6 blends display improvements in the mechanical behavior when compared with the neat HDPE matrix, e.g., up to 33% for the Young modulus, up to 119% for the ultimate tensile strength, and up to 80% for the flexural stiffness. Copyright © 2011 Society of Plastics Engineers.

Mechanical properties of structures 3D printed with cementitious powders

The three dimensional (3D) printing technology has undergone rapid development in the last few years and it is now possible to print engineering structures. This paper presents a study of the mechanical behavior of 3D printed structures using cementitious powder. Microscopic observation reveals that the 3D printed products have a layered orthotropic microstructure, in which each layer consists of parallel strips. Compression and flexural tests were conducted to determine the mechanical properties and failure characteristics of such materials. The test results confirmed that the 3D printed structures are laminated with apparent orthotropy. Based on the experimental results, a stress-strain relationship and a failure criterion based on the maximum stress criterion for orthotropic materials are proposed for the structures of 3D printed material. Finally, a finite element analysis was conducted for a 3D printed shell structure, which shows that the printing direction has a significant influence on the load bearing capacity of the structure.

Evaluation of mechanical, physical and thermal performance of cement-based tiles reinforced with vegetable fibers

The objective of this work was to analyze mechanical, physical and thermal performance of roofing tiles produced with several formulations of cement-based matrices reinforced with sisal and eucalyptus fibers. The physical properties of the tiles were more influenced by the fiber content of the composite than by the type of reinforcement. The type of the fiber was the main variable for the achievement of the best results of mechanical properties. Exposure to tropical climate has caused a severe reduction in the mechanical properties of the composites. After approximately four months of age under external weathering the toughness of the vegetable fiber-cement fell to 53-68% of the initial toughness at 28 days of age. The thermal performance showed that roofing tiles reinforced with vegetable fiber are acceptable as substitutes of asbestos-cement sheets. (c) 2006 Elsevier Ltd. All rights reserved.

Modeling the tensile behavior of fibers with geometrical and structural irregularities

Virtually all fibers exhibit some dimensional and structural irregularities. These include the conventional textile fibers, the high-performance brittle fibers and even the newly developed nano-fibers. In recent years, we have systematically examined the effect of fiber dimensional irregularities on the mechanical behavior of the irregular fibers. This paper extends our research to include the combined effect of dimensional and structural irregularities, using the finite element method (FEM). The dimensional irregularities are represented by sine waves with a 30 % magnitude of diameter variation while the structural irregularities are represented by longitudinal and horizontal cavities distributed within the fiber structure. The results indicate that fiber geometrical or dimensional variations have a marked influence on the tensile properties of the fiber. It affects not only the values of the breaking load and extension, but also the shape of the load-extension curves. The fiber structural irregularities simulated in this study appear to have little effect on the shape of the load-extension curves.

Effect of deformation schedule on the microstructure and mechanical properties of a thermomechanically processed C-Mn-Si transformation-induced plasticity steel

Thermomechanical processing simulations were performed using a hot-torsion machine, in order to develop a comprehensive understanding of the effect of severe deformation in the recrystallized and nonrecrystallized austenite regions on the microstructural evolution and mechanical properties of the 0.2 wt pct C-1.55 wt pct Mn-1.5 wt pct Si transformation-induced plasticity (TRIP) steel. The deformation schedule affected all constituents (polygonal ferrite, bainite in different morphologies, retained austenite, and martensite) of the multiphased TRIP steel microstructure. The complex relationships between the volume fraction of the retained austenite, the morphology and distribution of all phases present in the microstructure, and the mechanical properties of TRIP steel were revealed. The bainite morphology had a more pronounced effect on the mechanical behavior than the refinement of the microstructure. The improvement of the mechanical properties of TRIP steel was achieved by variation of the volume fraction of the retained austenite rather than the overall refinement of the microstructure.

Influence of helium atmospheric plasma treatment on surface and fracture-mechanical behaviour of quickstepTM cured bio-composites

This work investigated the potential of improving flexural properties of natural fiber (jute) reinforced biocomposites by atmospheric pressure helium plasma treatment. Composites were made by the use of combined hand lay-up and vacuum bagging technique followed by newly developed Australia patented Quickstep^TM curing. The physical properties of helium plasma modified fibers were investigated by means of wettability time, coefficient of friction (COF), atomic force microscopy (AFM) and chemical nature of the surface with ATR-FTIR and XPS. There was found a logical correlation between physical and chemical characteristics of the surface of fiber with the fracture mechanical behavior of their resulting biocomposites. In addition, the use of helium atmospheric plasma treatment prior to Quickstep^TM process has proved to be a potential way to positively alter the fracture-mechanical behavior of biocomposites. This study will lead to new commercial applications of natural fiber jute for the composite industry that go beyond wrapping and packaging.

Study of the effect of grain size on the dynamic mechanical properties of microalloyed steels

In the present paper the effect of grain refinement on the dynamic response of ultra fine-grained (UFG) structures for C–Mn and HSLA steels is investigated. A physically based flow stress model (Khan-Huang-Liang, KHL) was used to predict the mechanical response of steel structures over a wide range of strain rates and grain sizes. However, the comparison was restricted to the bcc ferrite structures. In previous work [K. Muszka, P.D. Hodgson, J. Majta, A physical based modeling approach for the dynamic behavior of ultra fine-grained structures, J. Mater. Process. Technol. 177 (2006) 456–460] it was shown that the KHL model has better accuracy for structures with a higher level of refinement (below 1 μm) compared to other flow stress models (e.g. Zerrili-Armstrong model). In the present paper, simulation results using the KHL model were compared with experiments. To provide a wide range of the experimental data, a complex thermomechanical processing was applied. The mechanical behavior of the steels was examined utilizing quasi-static tension and dynamic compression tests. The application of the different deformation histories enabled to obtain complex microstructure evolution that was reflected in the level of ferrite refinement.

Understanding the behavior of advanced high-strength steels using atom probe tomography

The key evidence for understanding the mechanical behavior of advanced high strength steels was provided by atom probe tomography (APT). Chemical overstabilization of retained austenite (RA) leading to the limited transformation-induced plasticity (TRIP) effect was deemed to be the main factor responsible for the low ductility of nanostructured bainitic steel. Appearance of the yield point on the stress-strain curve of prestrained and bake-hardened transformationinduced plasticity steel is due to the unlocking from weak carbon atmospheres of newly formed during prestraining dislocations.

Effect of temperature on mechanical behaviour of high manganese TWIP steel

The aim of the present study was to investigate the role of deformation temperature on the active deformation mechanisms in a 0.6C-18Mn-1.5Al (wt%) TWIP steel. The tensile testing was performed at different temperatures, ranging from ambient to 400°C at a constant strain rate of 10-3 S-1. The microstructure characterization was carried out using a scanning electron microscopy. The deformation temperature revealed a significant effect on the active deformation mechanisms (i.e. slip versus twinning), resulting in different microstructure evolution and mechanical properties. At the room temperature, the mechanical twinning was the dominant deformation mechanism, enhancing both the strength and ductility. Dynamic strain aging (DSA) effect was observed at different deformation temperatures, though it was more pronounced at higher temperatures. The volume fraction of deformation twins significantly reduced with an increase in the deformation temperature, deteriorating the mechanical behavior. There was a transition temperature (~300°C), above which the mechanical twinning was hardly observed in the microstructure even at fracture, resulting in low ductility and strength. The current observation can be explained through the change in the stacking fault energy with the deformation temperature. © (2014) Trans Tech Publications, Switzerland.

Achieving outstanding mechanical performance in reinforced elastomeric composite fibers using large sheets of graphene oxide

A simple fiber spinning method used to fabricate elastomeric composite fibers with outstanding mechanical performance is demonstrated. By taking advantage of the large size of as-prepared graphene oxide sheets (in the order of tens of micrometers) and their liquid crystalline behavior, elastomeric composite fibers with outstanding low strain properties have been fabricated without compromising their high strain properties. For example, the modulus and yield stress of the parent elastomer improved by 80- and 40-fold, respectively, while maintaining the high extensibility of ∼400% strain inherent to the parent elastomer. This outstanding mechanical performance was shown to be dependent upon the GO sheet size. Insights into how both the GO sheet size dimension and dispersion parameters influence the mechanical behavior at various applied strains are discussed.

Grain growth and β-Mg17Al12 intermetallic phase dissolution during heat treatment and its impact on deformation behavior of AZ80 Mg-alloy

Microstructure evolution after solutionizing and ageing treatment of cast AZ80 Mg alloy were investigated using optical and scanning electron microscopy. Effect of these treatments on grain size, β-Mg17Al12 intermetallic phase, mechanical behavior, and flow asymmetry were investigated. The initial continuous network of β-phase found to be reduced after solutionizing. The dissolution of β-phase and simultaneous grain growth are found to be interrelated. Mechanical properties including yield strength, maximum strength (ultimate compressive strength), and maximum strain attainable in compressive found almost twice than the corresponding values obtained in tension. The asymmetry in compressive and tensile properties is found to decrease with grain size at certain solutionizing duration. Particular heat treatment found to offer best combination of tensile compressive flow properties in AZ80 Mg alloy. Aging under certain conditions found to minimize the strength asymmetry. © ASM International.

Anisotropic behavior in plasticity and ductile fracture of an aluminum alloy

Anisotropic mechanical behavior is investigated for an aluminum alloy of 6K21-IH T4 both in plastic deformation and ductile fracture. Anisotropic plastic deformation is characterized by uniaxial tensile tests of dog-bone specimens, while anisotropy in ductile fracture is illustrated with specimens with a central hole, notched specimens and shear specimens. All these specimens are cut off at every 15º from the rolling direction. The r-values and uniaxial tensile yield stresses are measured from the tensile tests of dog-bone specimens. Then the anisotropic plasticity is modeled by a newly proposed J2-J3 criterion under non-associate flow rule (non-AFR). The testing processes of specimens for ductile fracture analysis are simulated to extract the maximum plastic strain at fracture strokes as well as the evolution of the stress triaxiality and the Lode parameter in different testing directions. The measured fracture behavior is described by a shear-controlled ductile fracture criterion proposed by Lou et al. (2014. Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality. Int. J. Plasticity 54, 56-80) for different loading directions. It is demonstrated that the anisotropic plastic deformation is described by the J2-J3 criterion with high accuracy in various loading conditions including shear, uniaxial tension and plane strain tension. Moreover, the anisotropy in ductile fracture is not negligible and cannot be modeled by isotropic ductile fracture criteria. Thus, an anisotropic model must be proposed to accurately illustrate the directionality in ductile fracture.

Mechanical properties of HIPS/sugarcane bagasse fiber composites after accelerated weathering

The effect of accelerated weathering on the visual appearance and on mechanical properties of high impact polystyrene (HIPS) as well as HIPS reinforced with mercerized and bleached sugarcane bagasse fibers composites are investigated. After accelerated weathering period of 900 h, under UV-B radiation and moisture regular cycles, changes in mechanical properties are investigated by tensile tests. Materials fracture surfaces are investigated by scanning electron microscopy (SEM). The study showed that the exposure time was sufficient to change the visual appearance of HIPS as the composites. From this study, it was observed that composites reinforced with bleached fibers are less susceptible to accelerated weathering exposure than composites reinforced with mercerized fibers, which is explained by the higher amount of lignin present in mercerized fibers. (C) 2010 Published by Elsevier Ltd. Selection and peer-review under responsibility of [name organizer]

What is the role of lipopolysaccharide on the tribocorrosive behavior of titanium?

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of partial crystallization on the mechanical properties and cytotoxicity of bioactive glass from the 3CaO center dot P2O5-SiO2-MgO system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)