Rolling of I-section beams using lead as a model material: Some experimental results

Results of a series of tests rolling $\text{I-}\text{section}$ beams in the first two passes, using lead as a model material, are presented; they include measurements of relative spread, natural elongation, roll load, roll torque and the observed changes in deformation modes with variation in shape factors (height to width ratios) of the specimens and the relative draughts.A comparison of these results is made with those obtained using empirical formulae suggested by earlier research workers. The observed rolling loads are compared also with measurements made of the die loads when rectangular specimens with the same shape factors as in these rolling tests were compressed between shaped dies having grooves similar to that in rolling and compressed under conditions of plane strain and in open-die compression.     

Crack detection in beams using experimental modal data and finite element model

In this paper, an analytical, as well as experimental approach to the crack detection in cantilever beams by vibration analysis is established. An experimental setup is designed in which a cracked cantilever beam is excited by a hammer and the response is obtained using an accelerometer attached to the beam. To avoid non-linearity, it is assumed that the crack is always open. To identify the crack, contours of the normalized frequency in terms of the normalized crack depth and location are plotted. The intersection of contours with the constant modal natural frequency planes is used to relate the crack location and depth. A minimization approach is employed for identifying the cracked element within the cantilever beam. The proposed method is based on measured frequencies and mode shapes of the beam.     

Multi-axial creep rupture of a model structure using a two parameter material model

A simplified, two parameter creep curve model is developed, which represents primary-secondary-tertiary creep behaviour. The two parameters are related via the secondary strain respectively to: the sum of secondary and primary strains; and, the sum of secondary and tertiary strains. Techniques are described for fitting the model to laboratory data; and, for the determination of the parameters which characterize primary-secondary and secondary-tertiary creep. The single state variable theory used to describe tertiary creep is compared with mechanisms based models and shown to closely predict the effect of stress-state on rupture strain. A two bar plane strain model component subjected to steady load is studied and used to determine the effect on the component lifetime of primary creep; and, of the multi-axial creep rupture criterion. The representative rupture stress is found to be weakly dependent on primary creep and strongly dependent on the multi-axial rupture criterion of the material.     

Generation of electrical energy using lead zirconate titanate (PZT-5A) piezoelectric material: Analytical,numerical and experimental verifications

Energy harvesting is the process of attaining energy from the external sources and transforming it into usable electrical energy. An analytical model of piezoelectric energy harvester has been developed to determine the output voltage across an electrical circuit when it is forced to undergo a base excitation. This model gives an easy approach to design and investigate the behavior of piezoelectric material. Numerical simulations have been carried out to determine the effect of frequency and loading on a Lead zirconate titanate (PZT-5A) piezoelectric material. It has been observed that the output voltage from the harvester increases when loading increases whereas its resonance frequency decreases. The analytical results were found to be in good agreement with the experimental and numerical simulation results.     

Large deflection of viscoelastic beams using fractional derivative model

This paper deals with large deflection of viscoelastic beams using a fractional derivative model. For this purpose, a nonlinear finite element formulation of viscoelastic beams in conjunction with the fractional derivative constitutive equations has been developed. The four-parameter fractional derivative model has been used to describe the constitutive equations. The deflected configuration for a uniform beam with different boundary conditions and loads is presented. The effect of the order of fractional derivative on the large deflection of the cantilever viscoelastic beam, is investigated after 10, 100, and 1000 hours. The main contribution of this paper is finite element implementation for nonlinear analysis of viscoelastic fractional model using the storage of both strain and stress histories. The validity of the present analysis is confirmed by comparing the results with those found in the literature.     

Design of a material handling equipment selection model using analytic hierarchy process

Selection of suitable material handling equipment for typical conditions and handling environment is found to be a multi-criteria decision making problem. The selection procedure is found to be unstructured, characterised by extensive domain dependent knowledge and requiring the application of an effective and efficient multi-criteria decision making tool, such as the analytic hierarchy process (AHP). The AHP technique breaks down decision making problems into finer parts to allow for easier and more logical selections. The following paper focuses on the application of the AHP technique in selecting the optimal material handling equipment under a specific handling environment. The relative importance of each criteria, subcriteria and sub-subcriteria is measured using pairwise comparison matrices and the overall ranking of each alternative equipment is then determined. Sensitivity analysis is performed to identify the most critical and robust criteria in the material handling equipment selection process.     

Mathematical model applied to the experimental calibration results of a capillary standard leak

Gas leaks supplied through metal capillaries are nowadays largely used in industry to calibrate “in situ” leak detectors (necessary in tightness tests, versus both vacuum and atmospheric pressure) or in whatever applications in which well-known (and very low) gas flows are necessary. If the capillaries are calibrated with a primary device or a reference one, the traceability of flow measurements to the national primary standards is guaranteed. At IMGC-CNR, standard leaks are calibrated by means of two primary flowmeters, operating respectively with reference to vacuum and to atmospheric pressure. In this paper, with the aim of developing a general calculus model for a unique calibration curve in both fields of use of a capillary leak, results relative to the calibration of a particular type of an all metal, crimped-capillary leak are presented and discussed. This capillary has been calibrated for helium, sulfur hexafluoride and nitrogen with reference both to vacuum and to atmospheric pressure and for molar flows ranging from about 1×10⁻¹¹ mol/s to 5×10⁻⁷ mol/s.     

An experimental work on using conductive powder-filled polymer composite cast material as tool electrode in EDM

This paper introduces the composite tool electrodes made of electrical conductive powder-filled polyester resin matrix material, providing promise for the electrical discharge machining (EDM) process. The dendrite-shaped copper powder, graphite powder, and their mixture were used as conductive fillers. Six different types of composite electrodes, namely, plain copper-polyester, pressed copper-polyester, furnaced copper-polyester, plain copper-graphite-polyester, pressed copper-graphite-polyester, and furnaced copper-graphite-polyester were prepared. It is found experimentally that increasing v _f improved workpiece material removal rate, tool wear rate, relative wear, and electrical conductivity of electrodes. The pressed copper-polyester electrodes were found to be promising in the ED finishing of workpieces at low machining current settings. The practical applicability of the proposed composite electrodes in the industry was also illustrated.     

A two-level optimization procedure for material characterization of composites using two symmetric angle-ply beams

A two-level optimization procedure for determining elastic constants E₁, E₂, G₁₂, and ν₁₂ of laminated composite materials using measured axial and lateral strains of two symmetric angle-ply beams with different fiber angles subjected to three-point-bending testing is presented. In the first-level optimization process, the theoretically and experimentally predicted axial and lateral strains of a [(45°/−45°)₆]_s beam are used to construct the strain discrepancy function which is a measure of the sum of the squared differences between the experimental and theoretical predictions of the axial and lateral strains. The identification of the material constants is then formulated as a constrained minimization problem in which the best estimates of shear modulus and Poisson's ratio of the beam are determined to make the strain discrepancy function a global minimum. In the second-level optimization process, shear modulus and Poisson's ratio determined in the first level of optimization are kept constant and Young's moduli of the second angle-ply beam with fiber angles different from 45° are identified by minimizing the strain discrepancy function established at this level of optimization. The suitability of the proposed procedure for material characterization of composite materials has been demonstrated by means of a number of examples.     

A decision-making framework model for material selection using a combined multiple attribute decision-making method

Material selection is a difficult and subtle task due to the immense number of different available materials. In choosing the right material, there is not always a single definite criterion of selection and the designers and engineers have to take into account a large number of material selection criteria. This paper presents a logical procedure for material selection for a given engineering design. The procedure is based on a combined TOPSIS and AHP method. The proposed material selection index helps to evaluate and rank the materials for a given engineering design. Two examples are included to illustrate the approach.     

Fault induction dynamic model,suitable for computer simulation: Simulation results and experimental validation

The study of induction motor behavior under not normal conditions and the ability to detect and predict these conditions has been an area of increasing interest. Early detection and diagnosis of incipient faults are desirable for interactive evaluation over the running condition, product quality guarantee, and improved operational efficiency of induction motors. The main difficulty in this task is the lack of accurate analytical models to describe a faulty motor. This paper proposes a dynamic model to analyze electrical and mechanical faults in induction machines and includes net asymmetries and load conditions. The model permits to analyze the interactions between different faults in order to detect possible false alarms. Simulations and experimental results were performed to confirm the validity of the model.     

橡胶波形发生器材料本构模型有限元仿真及试验研究

通过橡胶试件的拉伸、压缩试验,得出了两种硬度橡胶材料的应力-应变关系;建立两种硬度橡胶波形发生器的有限元模型,分别施加18 kN和28 kN的载荷,得到了采用不同本构模型的最大静态变形量及静态刚度;进行实物试验,并将有限元仿真结果与实物试验结果对比.研究表明:Arruda-Boyce模型相对误差最小,Van der Waals模型相对误差最大.     

硫化银纳米粒子 PVC膜银离子选择电极的研制

采用均相沉淀法制备了硫化银纳米粒子 , 给出了最佳制备工艺流程 . 用硫化银纳米粒子制作了 PVC 膜银离子选择电极 , 确定了敏感膜的最佳配比 . 对电极性能测量的结果表明 , PVC膜银离子选择电极的线性范围为 1.0× 10- 5～ 1.0× 10- 1mol/L, 检测下限为 2.0× 10- 6mol/L, 钾、钠、铅、钙、铜、锌等离子对电极测量无干扰 .     

The acting wear mechanisms on metal-on-metal hip joint bearings: in vitro results

Metal-on-metal (MOM) hip joint bearings are currently under discussion as alternatives to metal-on-polymer (MOP) bearings. Some criteria under scrutiny are the wear resistance, the influence of wear particles on the surrounding tissue, as well as the frictional torque. In order to understand and control the wear behavior of such a bearing a close correlation between the microstructures of the alloys used and the acting wear mechanisms has to be found. Thus, commercially available CoCrMo-balls were tested against self mating concave pins in a physiological fluid at 37°C under reciprocating sliding wear (1 Hz). The compressive load was 750 N (body weight). For 2×10⁶ cycles tests were carried out continuously and with periodically occurring resting periods. On the basis of the observed wear appearances the acting wear mechanisms are defined and evaluated as to their contribution to the wear behavior. Due to the high local contact stresses surface fatigue prevails initially. Cr– and Mo–carbides are fractured and torn off the surfaces bringing about additional surface fatigue by indentations and initiating abrasion. The weight loss can be predominately attributed to these mechanically dominated wear mechanisms. In a parallel occurring tribochemical reaction layers are generated from denatured proteins. These adhere rigidly to the surfaces and cover parts of the contacting surfaces avoiding adhesion. Thus, the wear behavior is mainly influenced by the alternating balance between surface fatigue and abrasion on the one side and by tribochemical reactions on the other side.     

Comparisons of experimental and numerical frequencies for classical beams carrying a mass in-span

A frequency analysis of an Euler–Bernoulli beam carrying a concentrated mass at an arbitrary location is presented. The dimensionless frequency equation for ten combinations of classical boundary conditions is obtained by satisfying the differential equations of motion and by imposing the corresponding boundary and compatibility conditions. The resulting transcendental frequency equations are numerically solved. A parametric study on the effects of the mass and its location for each respective case is presented. To verify the validity of the transcendental equations, the results for the fixed-fixed cases are compared with those obtained experimentally. On the other hand, approximate results are given, using the Rayleigh’s method with two static deflection shape functions. The effects of the position and magnitude of the mass, as well as comparisons of the different results obtained analytically, are investigated and discussed. The comparisons clearly show that the eigenfrequencies of the beam–mass system can be accurately predicted by solving the transcendental equation, whereas the closed-form Rayleigh’s expression is suggested for a quick estimation of fundamental frequency.     

ADC characterization by using the histogram test stimulated by Gaussian noise: Theory and experimental results

This paper presents results relating to the measurement of differential and integral nonlinearity of ADCs using the histogram method with white Gaussian noise as the stimulus signal. We specify the optimum noise power of the generator, in the sense of number of samples minimisation, as a function of the converter range and resolution. An expression of tolerance interval as a function of the number of samples acquired given a certain confidence level is presented both for the determination of transition levels (INL) and quantization intervals (DNL). Experimental and simulation results concerning the characterization of a 12-bit PC acquisition board are shown.     

Some properties of particleboards produced from Rhizophora spp. as a tissue-equivalent phantom material bonded with Eremurus spp.

The objective of this study is to evaluate the mechanical and physical properties of the particleboard manufactured from Rhizophora spp. in three particle sizes bonded with powdered Eremurus spp. root as a bio-based adhesive in two adhesive treatment levels. The samples acquired high internal bond strength values when the Rhizphora spp. particle size was reduced and the adhesive treatment level was increased. Dimensional stability normally increased with the reduced Rhizophora spp. wood particle size. The hydrophilic property of Eremurus spp. indicates that dimensional stability also increased with decreased adhesive treatment level. However, dimensional stability is affected by the adhesive treatment level when the wood particle size is smaller than that of the adhesive particle. The density distributions of the fabricated particleboards were evaluated using Surfer8 software, which showed significant homogeneity in all samples. The microstructures of the fabricated particleboards were investigated by field emission scanning electron microscopy, which refers to the better surrounding adhesive with bigger particles than Rhizophora spp. particles. This study indicates the potential of Eremurus spp. root as a bio-adhesive, which improved the characterization of Rhizophora spp. particleboard.     

Process parameters optimization of injection molding using a fast strip analysis as a surrogate model

Injection molding process parameters such as injection temperature, mold temperature, and injection time have direct influence on the quality and cost of products. However, the optimization of these parameters is a complex and difficult task. In this paper, a novel surrogate-based evolutionary algorithm for process parameters optimization is proposed. Considering that most injection molded parts have a sheet like geometry, a fast strip analysis model is adopted as a surrogate model to approximate the time-consuming computer simulation software for predicating the filling characteristics of injection molding, in which the original part is represented by a rectangular strip, and a finite difference method is adopted to solve one dimensional flow in the strip. Having established the surrogate model, a particle swarm optimization algorithm is employed to find out the optimum process parameters over a space of all feasible process parameters. Case studies show that the proposed optimization algorithm can optimize the process parameters effectively.