Curing behavior and viscoelastic properties of pine and wattle tannin-based adhesives studied by dynamic mechanical thermal analysis and FT-IR-ATR spectroscopy

This study investigated the curing behavior and viscoelastic properties of two types of tannin-based adhesives, wattle and pine, with three hardeners: paraformaldehyde, hexamethylenetetramine and TN (tris(hydroxylmethyl)nitromethane), by FT-IR-ATR spectroscopy and dynamic mechanical thermal analysis (DMTA). Using FT-IR-ATR spectroscopy, the chemical structures of tannin-based adhesives were determined and the degrees of curing as a function of temperature and time were compared with the conversion degrees of the hydroxyl groups. Paraformaldehyde was shown to be more reactive with wattle tannin than the other hardeners, while hexamethylenetetramine was the most reactive with the pine tannin. As the quantity of hardener was increased, the conversion degree also increased. The storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) of each adhesive system were obtained by DMTA. With increasing temperature, as the tannin-based adhesives hardened, the storage modulus (E′) increased in all adhesive systems. The curing behavior results obtained by DMTA showed a similar tendency as seen from the FT-IR-ATR spectroscopy results. The curing behavior of the tannin-based adhesives was successfully determined using FT-IR-ATR spectroscopy in combination with DMTA.     

On the Experiment Design for Direct Dynamic Parameter Identification of Parallel Robots

Accurate robot dynamic models require the estimation and validation of the dynamic parameters through experiments. To this end, when performing the experiments, the system has to be properly excited so that the unknown parameters can be accurately estimated. The experiment design basically consists of optimizing the trajectory executed by the robot during the experiment. Due to the restricted workspace with parallel robots this task is more challenging than for serial robots; thus, this paper is focused on the experiment design aimed at dynamic parameter identification of parallel robots. Moreover, a multicriteria algorithm is proposed in order to reduce the deficiencies derived from the single-criterion optimization. The results of the identification using trajectories based on a single criterion and the multicriteria approaches are compared, showing that the proposed optimization can be considered as a suitable procedure for designing exciting trajectories for parameter identification.     

Walking Pattern Generation for a Biped Walking Robot Using Convolution Sum

This paper describes a novel walking pattern generation method for a biped humanoid robot using a convolution sum. For a biped walking model, a single mass inverted pendulum model is generally used and the zero moment point (ZMP) equation is described by a decoupled linear differential equation. As a walking pattern generation method for the robot model, a novel method using a convolution sum is proposed in this paper. From the viewpoint of the linear system response, walking pattern generation can be regarded as a convolution of an arbitrary reference ZMP and the walking pattern for an impulse reference ZMP. For the calculation of convolution, the walking pattern for an impulse reference ZMP is first derived from the analytic walking pattern for a step reference ZMP. The convolution sum is then derived in two recursive forms, which can be applied online and offline, respectively. The proposed algorithm requires low computation power, since the walking pattern equation is composed of a recursive form. As the algorithm is expressed in analytic form, it is not necessary to solve optimization problems or calculate the fast Fourier transform, contrary to previous approaches. A computer simulation of walking demonstrates that the proposed algorithm yields excellent accuracy compared to the preview control method — one of the most highly regarded walking pattern generation methods. In addition, the application on the multi-point mass model is shown with the computer simulation.     

Determination of potency factor of cobalt for estimation of nickel equivalent in 16Cr–2Ni martensitic stainless steel

Abstract

Cobalt is considered to be a potential substitute for nickel in 16Cr–2Ni martensitic stainless steel. However, the percentage of cobalt that can substitute 1% of nickel remains to be determined. A computer program was developed for accurate prediction of δ ferrite content in Schaeffler type diagrams. The δ ferrite content in the steels was measured by metallography and estimated using the computation technique for various Schaeffler type diagrams. The percentage error in the experimentally measured and computed δ ferrite contents was ±1·0%. From the present study, the potency factor of cobalt was computed to be 0·64 that of nickel in the estimation of nickel equivalent.     

Thermomechanical fatigue behaviour of nickel base superalloy IN738LC Part 1 – Comparison of two unified constitutive models for description of mechanical behaviour

Abstract

The capabilities of two unified constitutive models to predict the mechanical behaviour of nickel base superalloy IN738LC under uniaxial loading conditions have been investigated over the temperature range 450–850°C. The material parameters of each model have been identified from an experimental investigation and complemented by available data from the literature. Mechanical responses from isothermal tests performed at 450 and 850°C (such as creep, monotonic, and fully reversed isothermal cyclic tests) were used for the identification of model parameters, and model capabilities were examined by comparison with in phase and out of phase thermomechanical fatigue and stress relaxation tests. Both models were found to capture all features of the material responses under uniaxial loading, although with varying degrees of accuracy.     

HEURISTIC MODELING FOR A DYNAMIC AND GOAL PROGRAMMING IN PRODUCTION PLANNING OF CONTINUOUS MANUFACTURING SYSTEMS

At the first sight it seems that advanced operation research is not used enough in continuous production systems as comparison with mass production, batch production and job shop systems, but really in a comprehensive evaluation the advanced operation research techniques can be used in continuous production systems in developing countries very widely, because of initial inadequate plant layout, stage by stage development of production lines, the purchase of second hand machineries from various countries, plurality of customers. A case of production system planning is proposed for a chemical company in which the above mentioned conditions are almost presented. The goals and constraints in this issue are as follows: ① Minimizing deviation of customer's requirements. ② Maximizing the profit. ③ Minimizing the frequencies of changes in formula production. ④ Minimizing the inventory of final products. ⑤ Balancing the production sections with regard to rate in production. ⑥ Limitation in inventory of raw material. The present situation is in such a way that various techniques such as goal programming, linear programming and dynamic programming can be used. But dynamic production programming issues are divided into two categories, at first one with limitation in production capacity and another with unlimited production capacity. For the first category, a systematic and acceptable solution has not been presented yet. Therefore an innovative method is used to convert the dynamic situation to a zero- one model. At last this issue is changed to a goal programming model with non-linear limitations with the use of GRG algorithm and that's how it is solved.     

A Tree-Based Alternative to Java Byte-Codes

Despite the apparent success of the Java Virtual Machine, its lackluster performance makes it ill-suited for many speed-critical applications. Although the latest just-in-time compilers and dedicated Java processors try to remedy this situation, optimized code compiled directly from a C program source is still considerably faster than software transported via Java byte-codes. This is true even if the Java byte-codes are subsequently further translated into native code. In this paper, we claim that these performance penalties are not a necessary consequence of machine-independence, but related to Java's particular intermediate representation and runtime architecture. We have constructed a prototype and are further developing a software transportability scheme founded on a tree-based alternative to Java byte-codes. This tree-based intermediate representation is not only twice as compact as Java byte-codes, but also contains more high-level information, some of which is critical for advanced code optimizations. Our architecture not only provides on-the-fly code generation from this intermediate representation, but also continuous re-optimization of the existing code-base by a low-priority background process. The re-optimization process is guided by up-to-the-minute profiling data, leading to superior runtime performance.