Applied Mechanics and Materials Vol. 657

Abstract: The paper presents the production orders sequencing issue, which main aim is to establish a proper sequence of tasks, that would maximize the utilization of companys production capacity. According to the literature research, the sequencing problem considered in the paper, may be denoted as CSP (Car Sequencing Problem) and belongs to the NP-hard class, as has been proven by simple reduction from Hamiltonians Path problem [1]. Optimal method of solution has not yet been found, therefore only approximate solutions have been offered [2]. Approximate solutions are based mainly on the evolutionary algorithms. However certain problems, as lack of possibility to check the effectiveness of the solution or the possibility to reach twice the same solution are observed. Regardless of the structure of specific assembly system, while considering reception of new tasks into the execution, current review of the state of the system is obligatory in order to decide whether, when and which new order can be accepted for assembly. In this paper, the problem of task scheduling is limited to the specific existing mixed-model production system. The main goal is to determine the effective method of creation of task sequence.

Abstract: Nowadays, oil wells drilling activities are performed with a large variety of equipment.

Abstract: Plasma nitriding has significant advantages: very low running costs (reduced consumption of energy and gases); optimized structure and layers; and nitriding of stainless steels. Plasma nitriding is totally safe and has no poisonous gas emissions and no negative environmental impact. However, conventional plasma nitriding has a number of well-known difficulties, including the direct application of plasma on the parts to be treated, the risk of arcing, hollow cathodes, white layers, non-homogenous batch temperature and the impossibility to mix parts of different geometries in the chamber made this technology to be almost forgotten. In the last years, due to the ecofriendly character of the technology, several atempts were made in order to establish an improvement in this technique in terms of batch damages. Active screen plasma nitriding technology is a new industrial solution that enjoys all the advantages of traditional plasma nitriding but does not have its inconveniences. A comparative study regarding quality surface and formed layer properties between conventional plasma nitriding and active screen plasma nitriding was conducted, in order to highlight the advantages that comes with this relatively new technique.

Abstract: These paper aims to present an experimental study for determining the mechanical properties of woven fabrics used for airbags manufacturing. In order to realise the study, there were chosen two types of fabric, one that is coated with silicon and one that is uncoated. The experimental tests that were carried out were uniaxial tension tests for samples extracted on the warp and on the weft direction, the Bias test, a test specific for shear loads and the dome test, a test specific for biaxial loads. For the uniaxial tension test the force-displacement curve was obtained and the maximum values of the loads and the displacement. For the last two tests (bias test and dome test) there have been determined the maximum load, the displacement at maximum load, but also the local major strains obtained. All tests were carried out on a tensile and compression testing machine Instron 5587, while for measuring the main strains there has been used also the optical measuring system Aramis.

Abstract: Performance evaluation of the polyester composites with added carbon nanotubes is presented herein, based on the results of compressive tests. Composites were obtained from polyester resin mixed with three types of carbon nanotubes: singlewall, multiwall and functionalized. The contents of carbon nanotubes were 0.1, 0.15 and 0.2 wt%. Cylindrical specimens with a diameter of 6 mm and a height of 9 mm were designed and prepared in conformity with the standards. Compressive tests were performed according to ISO 604, at the speeds of 1, 5, 10, 25 and 50 mm/min. Morfological study of the samples was carried out using SEM analysis. Dispersive X-ray spectrum in energy, associated with SEM micrograph, enabled to notice the elements existing in the composite. Stress-strain characteristics of polyester composite were determined through the compressive tests. The results revealed improved mechanical behavior of polyester composite, for test speed under 10 mm/min.

Abstract: Equi-qtomic NiTi (nitinol) shape memory alloy (SMA) is a good potential candidate material for use as thermo-mechanical actuator in a large variety of engineering like automotive and aerospace applications. Shape memory alloy in action are required to perform a large number of actuation cycles under cyclic thermo-mechanical loads and therefor are subject of fatigue. A shape memory alloy, supplied from Nimesis Technology, with martensite to austenite temperature transformation domain 76-80 °C. The material characteristics were investigated through differential calorimetry (DSC) before and after the thermo-mechanical solicitations. Under Joule effect and a timer, the active element goes up to 3000 cycles with a 500g weight on. The properties of thermo-elastic martensite transformation are the elastic accommodation of volume and shape change that takes place due to change in crystal structure upon phase transformation. A modification of the first coil of the intelligent arch-wire suffer a modification of the temperature transformation domain increasing the As and Af temperature values.

Abstract: Entire or partial loss of function in the shoulder, elbow or wrist represent an increasingly common ailment connected to a wide range of injuries or other conditions including sports, occupational, spinal cord injuries or strokes. A general treatment of these problems relies on physiotherapy procedures. An increasing number of metallic materials are continuously being developed to expect the requirements for different engineering applications including biomedical field. Few constructive models that can involve intelligent materials are analyzed to establish the advantages in usage of shape memory elements mechanical implementation. The shape memory effect, superelasticity and damping capacity are unique characteristics at metallic alloys which demand careful consideration in both design and manufacturing processes. The actual rehabilitation systems can be improved using smart elements in motorized equipments like robotic systems. Shape memory alloys, especially NiTi (nitinol), represent a very good alternative for actuation in equipments with moving dispositive based on very good actuation properties, low mass, small size, safety and user friendliness. In this article the actuation and the force characteristics were analyzed to investigate a relationship between the bending angle and the actuation real value.

Abstract: Due to ecological and sustainability constraints, in late years we see great achievements in green technology in the field of materials science. The development of high-performance biocomposites (made from natural resources) is increasing worldwide. The challenge in working with natural fiber reinforced composites is the large spectrum of possibilities for making them.Biocomposites properties are influenced by a number of variables, including the fiber type, environmental conditions (where the plant fibers are sourced), processing methods, and any modification of the fiber. It is well known that recently exists a large interest in the industrial applications of composites containing biofibers reinforced with biopolymers. The characteristics of reinforcing fibers used in biocomposites, including source, type, structure, composition, as well as mechanical properties, will be reviewed. The variety of biocomposite processing techniques as well as the factors (moisture content, fiber type and content, coupling agents and their influence on composites properties) affecting these processes will be discussed.Techniques for processing the natural fiber reinforced composites will be discussed based on thermoplastic matrices (compression molding, extrusion, injection molding, and thermoforming), and thermosets (resin transfermolding, sheet molding compound). Their influence on mechanical performance (tensile, flexural and impact properties) will be evaluated. Finally, the work will conclude with recent developments and future trends of biocomposites.

Abstract: In the paper analysis of surface topography influence on emissivity of metals was shown. This was performed for infrared band comprising wavelength region of 7.5 13 micrometers. Appropriate characterization and description of object emissivity has a crucial influence on accuracy of IR system for remote temperature measurement, e.g. IR thermography or pyrometry. These properties depend on many factors, including surface topography of material, where especially cavities play a very important role. In references so far emissivity are discussed mainly as influence of type of material (metal, dielectric), its temperature, wavelength or direction of emission. In the paper characterizing emissivity of construction materials in connection with 3D surface topography.

Abstract: Today conventional titanium-based alloys represent one third of the weight of modern aircraft engines and, are the second most used engine material following Ni-based superalloys. [1] Titanium aluminide alloys based on intermetallic phases γ (TiAl) and α₂ (Ti₃Al) and the most recent – orthorhombic titanium aluminide, are widely recognized as having the potential to meet the design requirements for high temperature applications. The outstanding thermo-physical and mechanical properties of these materials rely mainly on the strongly ordered nature and the directional bonding of the compounds. These involve: high melting point, above 1460°C, low density of 3,9-5 g/cm³, according the alloying degree, high elastic modulus (high stiffness), high yield strength and good creep resistance at high temperature, low diffusion coefficient, good structural stability at high temperature. The main objective of our paper are focussed on the short-term mechanical properties if Titanium niobium aluminide at 850°C. High temperatures mechanical properties evaluation was performed by tensile testing at temperature of 850°C on universal static and dynamic testing machine Instron 8802, equipped with high temperature system, for maximum 1000°C, and extensometer with a measuring basis of 40 mm. The mechanical tensile test was performed according the ASTM E8, with control of deformation and a testing rate of 10^-4 mmsec^.-1. Short-term behavior request of the support uncovered alloys, at 850°C has proved to be modest and it seems obvious that the alloys based on titanium aluminides cannot be used without protective coatings. Key words: titanium aluminides, high temperatures, mechanical properties