Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

Dissimilar welds impose a challenge to the engineers concerned with the structural integrity assessment of these joints. This is because of the highly inhomogeneous nature of these joints in terms of their microstructure, mechanical, thermal, and fracture properties. Fracture mechanics-based concepts cannot be directly used because of the problems associated with the definition of a suitable crack-tip loading parameter such as J-integral crack tip opening displacement (CTOD), etc. Again, depending upon the location of initial crack (i.e. base, weld, buttering, different interfaces, etc.), further crack propagation can occur in any material. The objective of the current work is to use micro-mechanical models of ductile fracture for initiation and propagation of cracks in the bimetallic welds. The authors have developed a finite element formulation that incorporates the porous plasticity yield function due to Gurson—Tvergaard—Needleman and utilized it here for the analysis. Experiments have been conducted at MPA Stuttgart using single edge-notched bend (SEB) specimens with cracks at different locations of the joint. The micro-mechanical (Gurson) parameters of four different materials (i.e. ferrite, austenite, buttering, and weld) have been determined individually by simulation of fracture resistance behaviour of SEB specimens and comparing the simulated results with those of the experiment. In order to demonstrate the effectiveness of the damage model in predicting the crack growth in the actual bimetallic-welded specimen, simulation of two SEB specimens (with initial crack at ferrite—buttering and buttering—weld interface) has been carried out. The simulated fracture resistance behaviour compares well with those of the experiment.

Operational modal analysis (OMA) is a procedure that allows the identification of the modal parameters of a structure using measured responses to unknown excitation. OMA techniques are based on the assumption that the input to the structure is stationary white noise. One of the OMA techniques, which is based on the assumption of a zero mean Gaussian white noise excitation, is the random decrement (RD) technique. In many practical cases, however, periodic excitation is often present in addition to the white noise. In this study, a method based on the concept of RD transformation is proposed to extract the response of a structure to the random input from the measured response that is due to both random and periodic excitations. Applying the RD method to the extracted random response, RD signatures were estimated. Modal parameters were estimated from RD signatures using the Ibrahim time domain algorithm. It is assumed that the period of the periodic excitation is known a priori. To verify the applicability of the method, a numerical simulation of a discrete two-degrees-of-freedom (DOF) dynamic system with a viscous damping is carried out. The results of this method were also compared with the results obtained from the enhanced frequency domain decomposition method. The efficiency of the proposed method, in the cases where the frequencies of harmonic components of periodic excitation are located at the natural frequencies of the system, is also evaluated.

The need of a better understanding of the dynamic behavior of systems has been showing the importance of the use of reliable methods to determine modal properties through the knowledge of output-only measurements. This article begins describing the theoretical bases of an efficient method for output-only system identification and an application example is demonstrated further. The studied system is a steel cantilever beam with a tip mass, which was tested at the Group of Applied Mechanics/Federal University of Rio Grande do Sul. Through free vibration tests, the response of the beam is acquired, and using the stochastic subspace system identification method (SSI), its dynamic properties are determined. Next, the beam is analysed by finite-element method and also through the theory of vibrations of continuous systems, determining its spectral properties. Thus, the results obtained through SSI are compared with the numerical and theoretical results, showing that the dynamic properties obtained through the procedure of system identification are reliable.

In this article, the dynamic analysis of an infinite Timoshenko beam made of a laminated composite located on a generalized Pasternak viscoelastic foundation is studied. The beam is subjected to a moving concentrated load. It is assumed that the mechanical properties of the beam change in the direction of the beam thickness but remain constant in the axial direction. Closed-form steady-state solutions, based on the first-order shear deformation theory, are developed. By selection of an appropriate displacement field for the composite beam, and using the principle of total minimum potential energy, the governing partial differential equations of motion are obtained and solved through a complex infinite Fourier transformation method. The results are introduced in terms of deflection, bending moment, shear force, and stress. In addition, the effects of stiffness, shear layer viscosity coefficients of foundation, velocity of the moving load, number of layers, and various angles of layers over the beam response are studied. For some specific cases, the results are compared with those presented in some other published papers, with which good agreements are observed.

An adaptive tuned vibration absorber (ATVA) can retune itself in response to a time-varying excitation frequency, enabling effective vibration attenuation over a range of frequencies. For a wide tuning range the ATVA is best realized through the use of a beam-like structure whose mechanical properties can be adapted through servo-actuation. This is readily achieved either by repositioning the beam supports (‘moveable-supports ATVA’) or by repositioning attached masses (‘moveable-masses ATVA’), with the former design being more commonly used, despite its relative constructional complexity. No research to date has addressed the fact that the effective mass of such devices varies as they are retuned, thereby causing a variation in their attenuation capacity. This article derives both the tuned frequency and effective mass characteristics of such ATVAs through a unified non-dimensional modal-based analysis that enables the designer to quantify the expected performance for any given application. The analysis reveals that the moveable-masses concept offers significantly superior vibration attenuation. Motivated by this analysis, a novel ATVA with actuator-incorporated moveable masses is proposed, which has the additional advantage of constructional simplicity. Experimental results from a demonstrator correlate reasonably well with the theory, and vibration control tests with logic-based feedback control demonstrate the efficacy of the device.

This article focuses on the modelling and control of a two-link planar mechanical manipulator that emulates a human arm. The simplicity of the control algorithm and its ease of computation are particularly highlighted in this study. The arm is subjected to a vibratory excitation at a specific location on the arm while performing trajectory tracking tasks in two-dimensional space, taking into account the presence of ‘muscle’ elements that are mathematically modelled. A closed-loop control system is applied using an active force control strategy to accommodate the disturbances based on a predefined set of loading and operating conditions to observe the system responses. Results of the study imply the effectiveness of the proposed method in compensating the vibration effect to produce robust and accurate tracking performance of the system. The results may serve as a useful tool in aiding the design and development of a tooling device for use in a mechatronic robot arm or even human arm (smart glove) where precise and/or robust performance is a critical factor and of considerable importance.

Continuing with the analysis performed for the one-dimensional axially loaded bar problem, a beam in bending is analysed to understand the influence of the characteristic parameters that have any influence in the solution of this problem using the element-free Galerkin method (EFGM), one of the most popular meshless methods. Both accuracy and time cost are considered as the evaluation functions to perform such an analysis. Both functions provide a reasonable idea to consider EFGM as an adequate method to solve the problem considered in this article. As in a one-dimensional axially loaded bar problem, the parameters to be considered will be those that affect the solution: number of nodes in which the domain is modelled, the nodes scatter, the order of the polynomial base to generate shape functions, the order of the quadrature to solve integrals, and the support radius. Besides, as in a one-dimensional axially loaded problem, some cases with different loading and stiffness conditions are considered. However, in this analysis a generalized moving least squares method is used to create shape functions instead of the moving least squares.

In a conventional one-dimensional scheme design of centrifugal fans and compressors, it is assumed that there is no flow prewhirl at the impeller inlet when the inlet guide vane is absent. However, many experiments have proved that the flow prewhirl does exist at the inlet of centrifugal impellers. This results in an error in the design of centrifugal fans and compressors. In this study a new method is presented to calculate the Euler work of centrifugal impellers considering the presence of an inlet flow prewhirl in the case without the inlet guide vane. Stodola's approach dealing with the slip velocity at the impeller outlet is applied to the impeller inlet. A new formula for Euler work calculation is deduced to evaluate the effect of the inlet prewhirl. The new formula has been applied to 33 industrial centrifugal fans and the calculated results have been compared with the experimental data of these fans. The comparison shows that the new formula is more accurate in most cases than the original formula without consideration of the inlet flow prewhirl, and the accuracy has been improved by more than 10 per cent on average. The aim of this study is to improve the accuracy of the one-dimensional scheme design of centrifugal fans and to provide a reference for a similar research.

Flow field in the plane of symmetry, upstream of circular and square cross-section blunt bodies mounted perpendicular to a flat plate with varying clearance between the obstacle tip and the flat plate, was experimentally studied in a water tunnel for a Reynolds numbers of 1400—3100. Qualitative aspects of the flow were captured using flow visualization. Detailed mapping of the flow field was carried out using planar particle image velocimetry (PIV). The existence of a multiple vortex system with characteristics similar to that of end-wall flows of surface-mounted obstacles with zero gap was noted. For large gap values, a jet-like flow was observed in the flow visualization; however, PIV measurements revealed the presence of the characteristic juncture vortex system even for such a configuration. The primary vortex of the square cylinder was observed to be further upstream as compared with the circular cylinder and moved closer to the cylinder surface with increasing Reynolds number. The vortex system for the square cylinder oscillated at a higher frequency. Increasing the tip gap resulted in the upstream movement of the primary vortex and reduction in amplitude and frequency of oscillation for both the cross-sections. The end-wall flow for the square cross-section cylinder was found to be more sensitive to variation in the tip gap.

The effect of thermal radiation on a steady two-dimensional natural convection laminar boundary layer flow of a viscous incompressible optically thick fluid over a vertical wavy frustum of a cone has been investigated. The boundary layer regime when the Grashof number Gr is large is considered. Using appropriate transformations, the basic governing equations are transformed into a dimensionless form and then solved numerically employing two efficient methods, namely: (a) implicit finite difference method together with Keller-box scheme and (b) direct numerical scheme. Numerical results are presented by streamline, isotherms, velocity and temperature distribution of the fluid, as well as the local shearing stress in terms of the local skin-friction coefficient, the local heat transfer rate in terms of local Nusselt number, and the average rate of heat transfer for a wide range of the radiation—conduction parameter or Planck number R_d and the surface heating parameter θ_w.

An optimal performance analysis of a parabolic-trough direct-steam-generation solar-driven Rankine cycle power plant at maximum power (MP) and under maximum power density (MPD) conditions is performed numerically to investigate the effects of heat loss from the heat source and working fluid. In this study, the ideal Rankine cycle of the solar-driven power plant is modified into an equivalent Carnot-like cycle with a finite-rate heat transfer. The main assumptions of this study include that: (a) the parabolic collector is the thermal reservoir at a high temperature, (b) the heat transfer process between the collector and the working fluid is through either radiation and convection simultaneously or radiation only, and (c) the heat transfer process from the working fluid to the low-temperature thermal reservoir is convection dominated. Comprehensive discussions on the effect of heat loss during the heat transfer process from the hot thermal reservoir to the working fluid in the parabolic-trough solar collector are provided. The major results of this study can be summarized as follows: (a) the working fluid temperature at the hot-side heat exchanger decreases remarkably whereas the working fluid temperature at the cold-side heat exchanger does not show any significant change with increasing heat loss, (b) the MP, MPD, and thermal efficiencies decrease with increasing heat loss, and (c) the effect of heat loss on the decrease of thermal efficiency increases when convection is the dominant heat transfer mode at the hot-side heat exchanger.

This article makes a detailed study of the influence of harmonics and the average undulation number of roundness profiles on the load bearing ability of interference-fitted assemblies. For this purpose, a plan of experiments was prepared by taking 3² factorial design with interference and the average undulation number as parameters. The analysis reveals that both the parameters influence the load bearing ability of interference-fitted assemblies. Further, it is found that harmonics influence the load bearing ability of interference-fitted assemblies.

This article presents a routine for prediction of the crack growth path in gears. Crack simulation helps in determining failure modes and crack detecting by vibration monitoring. To simulate crack propagation an effective method is developed by which the meshing force is calculated based on the compliance of meshing teeth in every stage of crack growth. In this method the compliance matrix of the tooth is calculated using three-dimensional boundary element analysis without the need for simultaneously modelling two meshing gears. The force distribution on the contact area is then calculated using Hertz theory and compliance matrices of meshing teeth. The method is used in prediction of the crack propagation path, meshing force, and meshing stiffness for two cases of ideal and misaligned meshing of a spur gear set. The crack propagation path is very different in the two cases of meshing and affects force distribution on a contact zone. Meshing stiffness reduces as crack propagates but the amount of reduction depends on the position of the contact line and crack propagation path.

Cavitation in a kinetic pump reduces delivery head and efficiency of the pump. It also causes mechanical damage and an increase of vibrations and noise. Therefore, it is important to detect inception and development of a cavitation phenomenon in the pump. This article deals with signals of vibration and noise, which will be used for detection and monitoring of the cavitation in kinetic pumps, and also to prevent the effect of the cavitation in the pump and pumping system. When the cavitation is increasing, the flowing conditions are changing, which leads to an increase of vibrations of the pump and emitted noise in the surroundings. Because vibrations and noise are transferred from the pump through its casing, the signal is non-uniformly distorted due to transfer losses and structure of the casing surfaces. Noise and vibrations are increasing steadily, but in some specific frequency ranges the signal is more pronounced than in other parts of the spectrum. Experimental results have shown that vibration and noise in the audible spectrum can be successfully used for cavitation detection and its prevention.

A hybrid actuator refers to a configuration combining the motions of two different electric motors with a mechanism to obtain a programmable output. This article presents an application of the genetic algorithm (GA) to determine optimal proportional-plus-integral-plus-derivative (PID) controller parameters to drive a seven link mechanism with an adjustable crank. A previously built model for a hybrid actuator system is used to explore the application. Simulation results are included to show how position control on both servomotors is achieved using GAs in off-line implementation.

For determining the globoidal cam profile with tapered rollers radially mounted at its turret, a direct and relative simple approach is presented. The concept of the proposed procedure is based on the cam surfaces that can be represented as the swept surfaces of the tapered roller of the globoidal cam-turret mechanism in motion. For finding the swept surfaces of the tapered roller, the pitch surface yielded by the locus of the tapered roller is first generated through the rigid body transformation. Then, in the process of producing the swept surfaces for the cam surfaces, the meshing angles and meshing vectors are defined and identified by using the pitch surface of the tapered roller. Since it is not necessary to solve any non-linear contact equations usually encountered in traditional methods, such a procedure provides a convenient tool in determining the spatial cam surfaces. To demonstrate the feasibility and accuracy of the proposed approach, its analytical formulations with numerical results are compared with those obtained by an earlier technique based on the theory of screws.

A pair of six-bar linkages, one of long vintage and the other very recent, are used as exemplars for considering their overall structures and the nature of their articulations. The two issues raised are the installation of an effective means for analysing a six-bar's gross mobility, and the extent to which exchanges might be made between linear and non-linear screw joints. Although the analytical tool applied is the well-known algebra of displacement—closure equations, it is the novel form of the relationships employed here that results in a successful outcome.

In the operations of optical inertial sensors, geometric variations due to temperature and operation environments cause thermoelastic deformations of their components, which lead to changes in the area and perimeter of their resonator block. The fluctuations in the geometric scale factor are corrected by the piezoelectric actuator. This article presents the numerical formulation of the elastic behaviour of each piezoelectric actuator, and the numerical formulations are verified through comparisons with the results of a finite element simulation.

This article introduces the concept of Assur virtual chains and its applications in differential kinematics of parallel manipulators. Using Assur virtual chains, the differential kinematics has a simple matricial formulation and the choice between direct and inverse kinematics is reduced to select primary variables in a homogeneous linear system. Assur virtual chains are also useful for obtaining information about the relative movements or to imposing particular kinematic constraints between two links of a kinematic chain. Additionally, a new systematic algorithm is established to analytically eliminate passive joint velocities and calculate the Jacobian matrices. This elimination approach is based on screw theory concepts such as twist, wrench, and reciprocity; also, graph theory is used for kinematic chain representation. At the end of the article, the method is applied to a 3RRR planar parallel manipulator and a general universal-prismatic-spheric Stewart—Gough platform.

This article deals with the reactive control of an autonomous robot, which moves safely in a crowded real-world unknown environment and reaches a specified target by avoiding static as well as dynamic obstacles. The inputs to the proposed neural controller consist of left, right, and front obstacle distance to its locations and the target angle between a robot and a specified target acquired by an array of sensors. A four-layer neural network has been used to design and develop the neural controller to solve the path and time optimization problem of mobile robots, which deals with cognitive tasks such as learning, adaptation, generalization, and optimization. The back-propagation method is used to train the network. This article analyses the kinematical modelling of mobile robots as well as the design of control systems for the autonomous motion of the robot. Training of the neural net and control performances analysis were carried out in a real experimental set-up. The simulation results are compared with the experimental results and they show very good agreement.

Thin films deposited on a phosphonate 3-aminopropyltriethoxysilane (APTES) self- assembled monolayer (SAM) were prepared on a hydroxylated silicon substrate by self-assembling. The chemical compositions and the chemical state of the film elements were determined by X-ray photoelectron spectrometry. The thickness of the films was determined with an ellipsometer, while the morphologies and nanotribological properties of the samples were analysed by atomic force microscopy. As a result, the target film was obtained. It was also found that the thin films showed the lowest friction and adhesion, followed by APTES—SAM and phosphorylated APTES—SAM, while the silicon substrate showed the highest friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear resistant than the other samples.

The electrical discharge machining (EDM) process is extensively used in the tool and die making industry for accurate machining of internal profiles in hardened materials. Although it is essentially a material removal process, efforts have been made in the recent past to use it as surface treatment method. This article investigates and compares the effect of material transfer from electrode bodies (copper, copper—chromium, and copper—tungsten) and tungsten powder suspended in the dielectric medium during die-sinking EDM of AISI H13 die steel. Results show a 76 per cent increase in micro-hardness by machining with a copper—tungsten electrode and a 111 per cent increase by machining with tungsten powder mixed in the dielectric. The copper—chromium electrode gives the best surface roughness (Ra) value of 2.67 μ m. Scanning electron microscopy and X-ray diffraction analysis of the machined surfaces show alloying of parent material with tungsten and tungsten carbide. Chemical composition of the machined surfaces was further checked on an optical emission spectrometer to verify the results. Besides a significant presence of tungsten, an increase in the percentage of carbon is also observed.