“Time-to-failure” prediction for a polymer-polymer swivelling joint

The growing competition in the market demands a better performance from any product in terms of availability, reliability, maintainability and failure free life. However there a number of engineering as well as environmental factor that influence the performance of a product. Wear is one of the critical factors, which influences the reliability and useful life of mechanical components. Therefore, the ability to predict wear at the development stage enables the designers to come up with a better design, longer useful life and more reliable products. Moreover, the prediction of time-to-failure for a component will lead to better maintenance helping to avoid catastrophic effects of unexpected failures. This paper presents a methodical approach for predicting sliding wear and hence the remaining useful life for a polymer-polymer sliding joint. The major stages of the approach are: tribo-system examination, experimentation, experimental wear coefficient determination and model formation.     

The Effects of Concentration, Relative Permittivity and Temperature on the Transport Properties of Sodium Polystyrenesulphonate in Methanol–Water Mixed Solvent Media

Precise measurements on the electrical conductivity of solutions of sodium polystyrenesulphonate in methanol–water mixed solvent media containing 8, 16, 25, and 34 wt.% of methanol at 308.15, 313.15, 318.15, and 323.15 K are reported. The degree of substitution of sodium polystyrenesulphonate used was 1, and the concentrations were varied from ∼2.0 × 10⁻⁴ to ∼4.0 × 10⁻³ monomol l⁻¹. The results showed a slight and monotonous increase in the equivalent conductivity with decreasing polyelectrolyte concentration. The applicability of the Manning’s theory for salt-free polyelectrolyte solution was examined and a major discrepancy against the theory was observed. The calculated values of the equivalent conductivity deduced on the basis of this theory were found to be lower than the experimental ones. Possible reasons for this discrepancy have been discussed. The effects of the temperature and relative permittivity of the medium on the equivalent conductivity were also investigated. Estimation of the fractions of uncondensed counterions provides important insight regarding the solution behavior of the polyelectrolyte in methanol–water mixtures.     

Optimum dynamic balancing of planar parallel manipulators based on sensitivity analysis

This paper addresses the optimum dynamic balancing of planar parallel manipulators exemplified with a 2 DOF parallel manipulator articulated with revolute joints. The dynamic balancing is formulated as an optimisation problem such that while the shaking force balancing is accomplished through analytically obtained balancing constraints, an objective function based on the sensitivity analysis of shaking moment with respect to the position, velocity and acceleration of the links is used to minimise the shaking moment. Sets of optimisation results corresponding to various combinations of the elements of the objective function are evaluated in order to quantify their influence on the resulting shaking moment, ground forces and the driving torques. The results prove that the proposed optimisation approach can be used to completely eliminate the shaking force and to minimise the shaking moment transmitted to the frame of the parallel mechanism. For parallel manipulators or mechanisms with higher degrees of freedom, for which it is virtually impossible to obtain shaking force balancing conditions analytically, we propose an alternative constrained optimisation procedure. This procedure is based on the fact that while the magnitude of either the shaking force or the shaking moment can be bounded through including a set of constraints in the optimisation algorithm, the sensitivities of the other, either those of the shaking force or the shaking moment, can be minimised.     

An experimental study on damage detection of structures using a timber beam

Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.     

Controlling floodwater mosquitoes by river regulation

Floodwater mosquitoes cause serious problems especially the spread of mosquito‐borne diseases. The main challenge is to implement acceptable general mitigation methods. In recent years, encouraging steps have been taken in favour of developing more sustainable measures such as modern biological methods. The novelty of the present study is in suggesting an alternative green method that can eliminate the use of any secondary biological or chemical agents. The method is based on establishing an alternative river regulation scheme that limits flooding of high‐risk lowland areas. A combined hydrodynamic modelling and optimization method gave effective river regulation schemes. The main idea is to maintain the total power production for a modified inflow hydrograph. The approach was applied to a 30‐km reach of the Österdalälven River located in central Sweden. It was found that with the specific constraints of the site a reduction of about 8% of lowland flood areas is possible if the inflow hydrograph is moderately modified by 20%. Higher reductions are possible by further modification of the hydrograph. The proposed method has a general character controlled by the specific site requirements of a critical flow or a water surface elevation. Based on the foregoing information, the method can be applied to similar sites.     

Constitutive Relationships for Steel Fibre Reinforced Concrete at Elevated Temperatures

Steel fibre reinforced concrete (SFRC) is an advanced cementitious composite where fibres can act as a profitable replacement for diffused reinforcement, like welded steel mesh, especially for thin cross sections. In this case fire becomes a very important condition in the design. Previous experimental research has shown the benefits in fire resistance of steel fibres, when structural elements are bent. The proper understanding of the effects of elevated temperatures on the properties of SFRC is necessary. In this study, constitutive relationships are developed for high-strength FRSC subjected to fire, with the purpose of given that capable modelling and to specify the fire-performance criteria for concrete structures. They are developed for unconfined FRSC specimens that include compressive and tensile strengths, modulus of elasticity, modulus of rupture, strain at peak stress, and compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish compressive stress–strain relationships. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

High Strength Polypropylene Fibre Reinforcement Concrete at High Temperature

Concrete is an inherently brittle material with a relatively low tensile strength compared to compressive strength. Reinforcement with randomly distributed short fibres presents an effective approach to the stabilization of the crack and improving the ductility and tensile strength of concrete. A variety of fibre types, including steel, synthetics, and natural fibres, have been applied to concrete. Polypropylene (PP) fibre reinforcement is considered to be an effective method for improving the shrinkage cracking characteristics, toughness, and impact resistance of concrete materials. Also, the use of PP fibre has been recommended by all of the researchers to reduce and eliminate the risk of the explosive spalling in high strength concrete at elevated temperatures. In this study, constitutive relationships are developed for normal and high-strength PP fibre reinforcement concrete (PPFRC) subjected to high temperatures to provide efficient modelling and specify the fire-performance criteria for concrete structures. They are developed for unconfined PPFRC specimens that include compressive and tensile strengths, elastic modulus, modulus of rupture, strain at peak stress as well as compressive stress–strain relationships at elevated temperatures. The proposed relationships at elevated temperature are compared with experimental results. These results are used to establish more accurate and general compressive stress–strain relationships prediction. Further experimental results for tension and the other main parameters at elevated temperature are needed in order to establish well-founded models and to improve the proposed constitutive relationships, which are general, rational, and fit well with the experimental results.     

Damage behaviour of laminated composites during fatigue loading

This study deals with the modelling of damage evolution in the carbon/epoxy laminated composites under static and fatigue loading. A cumulative damage model is developed on the basis of damage evolution due to static and fatigue during cyclic loading. A continuum damage mechanics (CDM)‐based damage model coupling with the micromechanics has been utilized to predict the fatigue behaviour of laminate composites. A multicriterion approach has been introduced to predict the damage behaviour in the longitudinal, transverse, and shear direction at the ply scale. Extensive experimental results on T300/EPL1012 carbon/epoxy laminates are prepared to characterize under static and fatigue loading and to evaluate the proposed model in different conditions. The obtained results show that at the beginning of the cyclic loading, the damage grows suddenly and increases until final failure, which justifies the proposed method is able to predict the evolution of the damage due to static and fatigue loading separately during cyclic loading. The obtained results show that considering damage due to static loading leads to more accurate results, particularly in low‐cycle fatigue.     

Heat treatment effect on the microstructure,tensile properties and dry sliding wear behavior of A356–10%B4C cast composites

In present paper, an attempt was made to examine the influence of T6 heat treatment (solution treatment at 540 °C for 5 h, quenching in hot water and artificial aging at 170 °C for 8 h) on the microstructure, tensile properties and dry sliding wear behavior of A356–10%B₄C cast composites. The composite ingots were made by stir casting process. In this work, the matrix alloy and composite were characterized by optical microscope, scanning electron microscope equipped with energy dispersive X-ray spectroscopy, tensile tests and conventional pin-on-disk experiment.     

Isothermal aging effect on the microstructure and dry sliding wear behavior of Co–28Cr–5Mo–0.3C alloy

In this study, an attempt to investigate the role of isothermal aging on the microstructure and dry sliding wear behavior of Co–28Cr–5Mo–0.3C alloy was made. Regarding the results, it is clear that isothermal aging at 850 °C for 8 and 16 h contributed to the formation of lamellar type carbides (γ-fcc + M₂₃C₆) at the grain boundary regions. Moreover, at higher aging times (24 h), the lamellar type carbides decreased whereas severe precipitation of carbides was found to occur on the stacking faults. Furthermore, according to X-ray diffraction results, 24 h isothermal aging of solution treated specimens did not lead to complete fcc → hcp transformation. The wear properties of as-cast and heat treated samples were determined at 0.5 ms⁻¹ speed several under normal applied loads such as 50, 80, and 110 N. At the lowest load applied (50 N), isothermally aged specimens for 8 and 16 h have higher wear resistance probably due to more volume fraction of lamellar-type carbides when compared to as-cast for both 4 and 24 h aged specimens. But, at higher applied loads (80 and 110 N) due to the formation of adhesive oxide layer on the as-cast specimen surface, the wear rate of as-cast samples is lower compared with all heat treated specimens.