Bounded Elastic Moduli Multiplier Technique for Limit Loads: Part 1 - Theory

Statically admissible stress distributions are necessary to evaluate lower bound limit loads. Over the last three decades, several methods have been postulated to obtain these distributions using iterative elastic finite element analyses. Some of the pioneering techniques are the reduced modulus, r-node, elastic compensation, and linear matching methods, to mention a few. A new method, called the Bounded Elastic Moduli Multiplier Technique (BEMMT), is proposed and the theoretical underpinnings thereof are explained in this paper. BEMMT demonstrates greater robustness, more generality, and better stress distributions, consistently leading to lower-bound limit loads that are closer to elastoplastic finite element analysis estimates. BEMMT also questions the validity of the prevailing power law based stationary stress distributions. An accompanying research offers several case studies to validate this claim.

The structure and mechanical properties of Cr-based Cr-Ti alloy films

Previous studies have dealt with Cr and its alloy films that exhibit promising characteristics as surface modification layers for antiwear, anticorrosive, and decorative applications. However, the effect of Ti alloying on the structure and mechanical properties of Cr films has not been studied. This work aimed to the structure and mechanical properties of Cr-Ti alloy films in the Cr-rich side. To this end, pure Cr, Cr-6 at.% Ti, Cr-11 at.% Ti, Cr-16 at.% Ti, and Cr-21 at.% Ti alloy films were prepared by magnetron sputtering, and the structure and mechanical properties of the films were evaluated. The results indicated that all the films exhibited a Cr-based growth with body-centered cubic structure, and increasing the Ti content decreased the (110) orientation growth of Cr basis. Ti alloying increased the hardness of the films, while leaded to a monotonic decrease in the modulus of the films. The first-principles method was employed to demonstrate that the reduced modulus was determined by the Ti alloying degree, rather than the orientation evolution of the films. The analysis of H/E value suggested that the wear resistance of the films was improved by Ti alloying. The mechanical properties of present Cr-Ti alloy films, and other Cr-based alloy films or metallic glasses in publications were compared and discussed. We proposed that Ti alloying is a considerable way to explore advanced mechanical properties of Cr-based alloy films.

Stress-strein state of weak and filled soils reinforced with reinforced concrete and soil piles, respectively

Introduction. The overwhelming majority of construction areas are characterized by difficult engineering and geological conditions, represented by the presence of weak soils at the base. There are construction sites on which a large thickness of fill soil is observed. In these conditions, designers apply: soil consolidation, soil reinforcement, significant deepening of the underground part of buildings, etc. This article presents the formulation and solution of the problems of interaction of reinforced concrete piles with weak soils, as well as the interaction of soil piles with bulk soils as part of a pile-slab foundation, which allow one to determine the reduced deformation modulus and the bedding value. Materials and methods. To describe the change in shear stresses depending on depth, a law was adopted in the form τ(z)=τ0е–αz. The solution is presented by analytical and numerical methods. The results obtained were compared by the analytical solution of the problem with the results obtained in the PLAXIS 3D software package. Results. Regularities of the distribution of the total load on the pile-slab foundation between the pile field and the grillage have been obtained. The analytical solutions in the article are supported by the graphical part, performed using the Mathcad program. Numerical simulation of the problem was carried out in the PLAXIS 3D software package. The dependence of the settlement on the load, calculated by analytical and numerical methods, is shown. An expression is obtained for defining the stresses in different sections of the pile shaft and under the grillage slab. The theoretical and practical aspects of the construction of crushed stone piles are considered. The theoretical substantiation of compaction of bulk soils with crushed stone piles using a special technology is given. A dependence is obtained for determining the reduced modulus of deformation for bulk soil mass reinforced with soil piles. Conclusions. Comparative evaluation of the results of solutions obtained by analytical and numerical methods showed good convergence. The solutions obtained can be used to preliminary determination of the settlement of piles as part of a pile-slab foundation. Selection of the optimal ratio of the pile length and its diameter allows the most effective use of the bearing capacity of the pile. For bulk soils, reinforced with soil piles, it is possible to select the optimal reduced modulus of deformation by varying the pitch of the soil piles.

Characterization of bilayer (FeB/Fe2B) on AISI H13 work tool steel

In this work, the borided layers were produced on AISI H13 steel via solid boriding with a powders mixture containing 90 wt.% B4C and 10 wt.% NaBF4 for treatment times of 2-6 h at 900, 950 and 1000 °C. The microscopic observations revealed a less pronounced toothed interface between the borided layer and the transition zone. The XRD studies indicated the presence of a dual phase boride layer (FeB/Fe2B) besides the chromium and vanadium borides as precipitates inside it. The boronizing kinetics of AISI H13 steel was investigated by using the classical parabolic growth law. The obtained value of boron activation energy in the entire boride layer (FeB + + Fe2B) was found to be 236.34 kJ mol-1. Furthermore, this value of energy has been compared to the literature data. Finally, the nanohardness and reduced modulus of elasticity were measured for FeB, Fe2B and transition zone.

Effect of thickness and matrix variability on properties of a starch-based nanocomposite supple film

In this research, the effects of matrix variability and thickness on the properties of a flexible nanocomposite film were investigated. The nanocomposite film was prepared from the blends of 1 kg cassava starch, 45–55% (w/v) glycerol and 0–2% (w/v) zincnanoparticles in thickness ranging from 15 −17 µm. The barrier, mechanical, and thermal properties were determined experimentally. The optimal effects of the thickness and the matrix variability on the properties were determined using Response Surface Methodology. Results showed that the barrier properties increased with glycerol concentration but decreased with thickness. Reduced modulus and tensile strength increased with an increase in the matrix variability. The film was thermally stable up to 60.43oC with only 2% degradation. The optimal film contains 55% glycerol, 2% zinc nanoparticles with a thickness of 17 µm at a desirability index of 0.95. This can therefore be essential for industrial application

Preparation of p-Phenylenediamine Modified Graphene Foam/Polyaniline@Epoxy Composite with Superior Thermal and EMI Shielding Performance

With the development of integrated devices, the local hot spot has become a critical problem to guarantee the working efficiency and the stability. In this work, we proposed an innovative approach to deliver graphene foam/polyaniline@epoxy composites (GF/PANI@EP) with improvement in the thermal and mechanical property performance. The graphene foam was firstly modified by the grafting strategy of p-phenylenediamine to anchor reactive sites for further in-situ polymerization of PANI resulting in a conductive network. The thermal conductivity (κ) and electromagnetic interference shielding (EMI) performance of the optimized GF/PANI4:1@EP is significantly enhanced by 238% and 1184%, respectively, compared to that of pristine EP with superior reduced modulus and hardness. Such a method to deliver GF composites can not only solve the agglomeration problem in traditional high content filler casting process, but also provides an effective way to build up conductive network with low density for thermal management of electronic devices.

Effects of Fatigue Damage on the Microscopic Modulus of Cortical Bone Using Nanoindentation

Alterations to the bone structure from cycle loadings can undermine its damage resistance at multiple scales. The accumulation of fatigue damage in a bone is commonly characterized by the reduction in the elastic modulus. In this study, nano-indentation was used for investigating microscopic damage evolution of bovine tibia samples subjected to fatigue loading. Indentation tests were conducted in the same 60 μm × 120 μm area with different degrees of damage, including fracture, and the evolution of reduced modulus was observed. The results showed that bone’s reduced modulus decreased significantly during the initial 40% of the life fraction, whereas it proceeded slowly during the remaining period. As the size of the residual indentations was about 4 μm in length, the degradation of bone’s reduced modulus reflected the accumulation of fatigue damage at smaller scales.

Nanomechanical behaviour of ZrO2 dispersed sisal-based polymeric composites

Alkali-treated sisal fibre-incorporated silanized ZrO2 dispersed unsaturated polyester composites were fabricated with a filler loading of 5, 15, 25, 35, 45 wt%, respectively. The mechanical characterization of the composites was suitably executed at the sub-micron scale using the nanoindentation technique. Various mechanical properties were derived from the standard nanoindentation measurements namely, nanohardness, reduced modulus, recovery index, residual depth, wear rate and indentation creep, respectively. A marked improvement in the mechanical properties of the unsaturated polyester matrix due to the incorporation of the fillers (sisal and/or ZrO2) was observed through indentation-derived parameters namely, nanohardness (∼186%), reduced modulus (∼175%), recovery index (∼62%), wear rate (∼63%) and indentation creep (∼33%), respectively. A simulated dynamic mechanical analysis was performed using the sinus mode of the nanoindentation technique. A similar enhancement in the dynamic mechanical properties of the matrix was further observed through dynamic mechanical analysis as storage modulus (∼71%), loss modulus (∼60%), loss factor (∼150%) and specific damping coefficient (∼200%), respectively.

The Effect of Blast Exposure Distance on Hardness and Reduced Modulus Properties of Lead-Free Solder

This study discussed the effect of blast exposure distance of lead-free solder on micromechanical properties. Sn-Ag-Cu solder samples were exposed to 1000 g of Plastic Explosive. The soldered samples were placed at a distance of 1 m, 2 m and 4 m distance from the blast source. In order to study micromechanical properties in localized and more details, the nanoindentation approach was used. The indentation was performed at the center of the solder to examine the hardness and reduced modulus properties. The load-depth curve of indentation for 1 m distance from the blast source has apparent the discontinuity during loading as compared to the control sample. The hardness value increased as the distance from the blast source increased. The shortest distance from the blast source gives a high impact on the degradation of hardness properties as compared to others. This result is important in assessing the effect of exposure distance from the blast source.

Effect of Gamma Radiation on Micromechanical Behaviour of SAC305 Solder

Electronic packaging is the technology concerning to the establishment of electrical interconnections and it is a major discipline within the field of electronics engineering. Packaging of an electronics system should considered the protection from mechanical damage, cooling, radio frequency noise emission and protection from electrostatic charge. Solder alloys have been extensively used as interconnection materials for microelectronic package. Solder joint in radiation environment requires higher reliability and resistance to any damage caused by ionizing radiation. The electrical failure during radiation has proved that the reliability of solder joint is importance and sensitive to the service condition. In this study, a lead-free solder alloy, SAC305 (96.5Sn3.0Ag0.5Cu wt.%) were prepared into two batches, which are unirradiated and irradiated batches with the various doses 5, 50, 500 Gy of gamma radiation. Nanoindentation was used in order to investigate the effect of the radiation to micromechanical properties such as hardness, H and reduced modulus, E of the solder. The results showed that the SAC solder changed when exposed to gamma rays. The hardness of the specimens calculated from the nanoindentation were decreased to 195.4 from 279.6 MPa with the increasing of radiation dose. These values of hardness are also lower than the hardness of non-irradiated sample indicating possible radiation damage and needs further related atomic dislocation study. The reduced modulus for irradiated specimens significantly increased as well, with values from 25.6 to 123.9 GPa after exposure. The increment of the reduced modulus occurred as a result of strain hardening or softening of the solder.