Optimal Thermo-mechanical Properties Research Articles

Physicochemical and thermomechanical performances study for Timahdite sheep wool fibers application in the building's insulation

The present research focuses on the development and thermomechanical characterization of unfired solid bricks based on clay (white and red) and Timahdite sheep wool, which are local, durable, abundant, and economical materials. As this clay material is incorporated with sheep wool in the form of yarn multi-layers in opposite directions. It achieves good thermal and mechanical performance and a lightness of these bricks as acquired progress. This new method of reinforcement offers significant thermo-mechanical performance for the composite for thermal insulation in sustainable buildings. Several physicochemical analyses to characterize the raw materials were used. Thermomechanical measurements to characterize the elaborated materials. The wool yarn effect was significant on the mechanical behavior of the developed materials at 90 days, with flexural strength from 18 to 56% for the white clay. And 8–29% for the red one. Decrease in compressive strength from 9 to 36% for the white clay and 5–18% for the red one. These mechanical performances are accompanied by thermal conductivity gain ranging from 4 to 41% for the white and 6–39% for the red for wool fractions: 6–27 g. This green multi-layered bricks from abundant local materials with optimal thermo-mechanical properties, qualified for the intended use for thermal insulation and energy efficiency in the construction and development of local economies.

A new experimental strategy assessing the optimal thermo-mechanical properties of plaster composites containing Alfa fibers

In recent years, building materials with a sustainable and reusable aspect, have gained an important position in the modern construction market. The main objective of this work is to evaluate the plaster thermo-mechanical properties according to three major influential parameters, which are mixing water ratio, natural additive concentration and interaction structure between the fibrous system and the plaster matrix. However, the EI700 cell, also called the two-box method, was utilized to perform the thermo-physical characterization, while the bending tests allowed to identify the mechanical performances. From a thermal point of view, the results achieved reveal the positive effect brought by the increase of fiber dosage and water blending rates, on the enhancement of the thermal qualities. On the other hand, the mechanical assays demonstrated that incorporating fibers within the plaster enables decreasing its resistance to bending, but in contrast it improves significantly the failure mechanism, thus providing a nonlinear and ductile behavior. Finally, the optimal material determination, illustrated that the random distribution of the cut fibers in the main matrix network was concluded as the best solution to obtain composites with excellent thermo-mechanical properties.

Liquid Crystal Polymer for QFN packaging: Predicted thermo-mechanical fatigue and Design for Reliability

Thermoplastic resins, such as Liquid Crystal Polymers (LCPs), have many attractive properties for microelectronic cavity package manufacturing (in particular low gas permeation and low dielectric constant). In order to reduce anisotropic mechanical properties inducing a potential fragility of the material and then a lack of reliability of the package, various approaches are currently studied in particular the addition of mineral fillers. A dedicated Design of Experiments (DoE) is performed to assess the optimal thermo-mechanical properties of the LCP compound and then the optimal composition of the package leading to the maximum operating lifetime. In this way the long-term reliability of an electronic package (Quad Flat No-lead – QFN – package) based on various formulations of the LCP composite is assessed by thermo-mechanical simulation using Finite Element Method (FEM). A Design for Reliability (DfR) methodology is proposed according to the simulation results based on Taguchi methodology. This methodology allows the determination of the optimal composition (nature/proportion/size/chemical functionalization of fillers) of the LCP package by reducing the number of experimental studies that are very time consuming.

Synthesis of (meth)acrylate water-borne latexes using amino-acid based surfactants: effect of surfactant on film properties

The rapidly increasing concern over environmental changes necessitates the employment of ecologically friendly surfactants for use in emulsion polymerisation without, however, compromising the latex stability or the properties of the cast films. To this end, three series of water-borne, lightly cross-linked latexes based on methyl methacrylate and butyl acrylate were prepared by free radical emulsion polymerisation. 1,4-Butanediol diacrylate served as the cross-linker. Each of the latex series was stabilised by one anionic, amino-acid based surfactant, namely: sodium lauroyl sarcosinate (SLSar), sodium myristoyl sarcosinate (SMSar) and sodium lauroyl glutamate (SLGlu). For comparison purposes, latexes stabilised by sodium dodecyl sulfate (SDS) were also prepared. Within each family, the monomer-to-surfactant molar ratio was varied systematically, whereas the monomer and initiator contents were kept constant in all cases. The hydrodynamic radii (Rh) and the radii of gyration (Rg) of the particles were found to systematically increase with increasing monomer-to-surfactant molar ratio. Films prepared from the SLSar and SDS stabilized latexes were investigated in terms of their optical and thermomechanical properties using transmittance experiments, differential scanning calorimetry, tensile strength and creep experiments. Optimal thermomechanical properties were observed for a particular monomer-to-surfactant molar ratio. Moreover, for the same monomer-to-surfactant molar ratio, the SLSar-based films exhibit remarkable resistance to breaking compared to their SDS counterparts that are relatively fragile.

Structure and Shape Memory Properties of Polyurethane Copolymers Having Urethane Chains as Soft Segments

Shape memory polyurethanes are usually fabricated with low-molecular weight polyols through a two-step copolymerization, which often results in difficulty attaining both desired shape memory switch temperature and optimal thermomechanical properties. Here we present a series of shape memory polyurethane copolymers having urethane chains as soft segments. The structure and shape memory properties of copolymers were investigated with differential scanning calorimetry, dynamic mechanical analysis, small angle x-ray scattering, and thermomechanical tests. Increasing the length of the urethane soft segments enhanced phase separation, while it brought little change to the glass transition temperature (T g). Based on the urethane soft segments, some rigid chain extenders could be readily introduced into the backbone of copolymers, resulting in better phase separation. All polyurethane copolymers exhibited more than 90% of shape recovery. The shape recovery of the materials was proved to be inversely proportional to the fraction of hard phase and directly proportional to the stability of hard domains. The copolymers containing longer soft and hard segments and rigid chain extenders exhibited higher deformation stress and thus larger recovery stress. The copolymerization employing urethane chains as soft segments can greatly expand flexibility for molecular design and favor the optimization of shape memory properties.

2D thermo-mechanical contact simulations in a functionally graded material: A multigrid-based approach

The development and selection of coatings or coating combinations is a complex and costly task. Numerical simulations provide a great help to analyze the behavior of coatings and layer interfaces under mechanical and thermal loading through the computation of stress and strain fields. They are also used to fine tune the geometrical configuration and define optimal thermo-mechanical properties related to the applied stress to enhance wear and crack resistance. Coating design has been based mainly on discrete layer models with abruptly changing properties at interface perfectly bonded to a substrate. These assumptions result in discontinuities in stress and temperature fields at the interface between successive layers. These models are based either on integral transform (classically Fourier transform) or finite element (FE) methods. The former cannot handle 3D thermo-mechanical problems. The latter demands huge calculation times, especially when considering thin layers with very small elements. The aim of this paper is to account for materials with continuously changing properties and to obtain an improved prediction of the resistance of such graded materials. This gradation may be linked to surface treatments like nitruration, thermal treatment, … or to the deposition of coatings inducing diffuse boundaries between those dissimilar materials. The proposed model aims at providing valuable description and understanding of the behavior and resistance of such graded material. It is based on a second order finite difference (FD) formulation of the continuous thermal and elasticity equations. It can handle any kind of depth dependence of the material properties. Multigrid techniques are implemented to accelerate the convergence, reduce CPU time and thus permit the use of fine grids to accurately describe the variation in the material properties. The first step of this project consists in implementing the above-cited numerical techniques in a 2D plane strain model.