Rapid Tempering of Martensitic Stainless Steel AISI420: Microstructure,Mechanical and Corrosion Properties

In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.     

Tracking the sources of salmonella in ground beef produced from nonfed cattle

The objective of this study was to determine the source(s) of Salmonella contamination in ground beef. One hundred dairy cows were harvested in a U.S. commercial beef processing plant. Samples of hides, carcasses after hide removal and before exposure to antimicrobial intervention, carcasses after all antimicrobial interventions, superficial cervical lymph nodes from the chuck, trim, ground beef, and air were obtained. Ninety-six percent of the hide samples, 47% of the carcasses before intervention, 18% of the lymph nodes, 7.14% of the trim, and 1.67% of the ground beef samples were positive for Salmonella. None of the samples obtained from the carcasses after the full complement of interventions and none of the air samples were positive for Salmonella. All Salmonella-positive samples were subjected to pulsed-field gel electrophoresis, and eight DNA Xba I restriction patterns were identified. The majority of isolates had one of two restriction digest patterns. The strain isolated from ground beef had the same pattern as the strains isolated from hides and from carcasses immediately after hide removal. The Salmonella isolates from trim samples and lymph nodes also had the same restriction digest pattern. These results indicate that hide and lymph nodes are the most likely sources of Salmonella in ground beef. Dressing practices that effectively reduce or eliminate the transfer of bacteria from hide to carcass and elimination of lymph nodes as a component of raw ground beef should be considered as measures to reduce Salmonella contamination of ground beef. Because total elimination of lymph nodes from ground beef is not possible, other approaches should be explored. Easily accessible lymph nodes could be screened for Salmonella very early in the slaughter process. When the results are positive for Salmonella, the corresponding carcasses should be fabricated separately at the end of the production run, and the trim from these carcasses should be subjected to a treatment that destroys Salmonella.     

Evaluating the safety impacts of the number and arrangement of lanes on freeway exit ramps

The primary objective of this study is to evaluate the impacts of the number and arrangement of lanes on freeway exit ramps on the safety performance of freeway diverge areas. The research team collected crash data at 343 freeway segments in the state of Florida. Four different types of exit ramps were considered in this study. They were defined as type 1, type 2, type 3, and type 4 exit ramps respectively. Cross-sectional comparison was conducted for comparing crash frequency, crash rate and crash severity between different types of freeway exit ramps. Crash prediction models were developed to identify the factors that contribute to the crashes reported at selected freeway segments and to provide quantified information regarding the safety impacts of different freeway exit ramps. It was found that the ramp and freeway AADT, posted speed limit on freeway, deceleration lane length, right shoulder width, and the type of exit ramp significantly affected the safety performance of freeway diverge areas. The study demonstrated the safety benefits of using lane-balanced exit ramps. Based on the crash prediction models, replacing a type 1 exit ramp (lane-balanced) with a type 2 exit ramp (not lane-balanced) will increase crash counts at freeway diverge areas by 68.33%. Replacing a type 3 ramp (lane-balanced) with a type 4 ramp (not lane-balanced) will increase crash counts at freeway diverge areas by 32.20%.     

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.     

“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.     

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.     

Improved Dissolution of Indomethacin in Coprecipitates with Phospholipids-I

Indomethacin powders were blended with phospholipids to prepare physical mixtures or made into solid dispersions by the solvent method and their comparative dissolution profiles were studied. Indomethacin exhibited significantly improved dissolution rates in phospholipid coprecipitates compared to either the physical mixtures or the pure indomethacin. The coprecipitates of lecithin-indomethacin 1:16 weight ratio had a 6.5 fold greater initial dissolution rate, and the total amount dissolved after 60 minutes was 140% greater compared to indomethacin alone. Increasing the lecithin content to 1:4 resulted in only a modest additional increase in the initial dissolution rate (40%) and the limiting concentration (14%)