Materials Science Forum Vol. 812

Abstract: The objective of our work is to improve the mechanical stiffness of fiber reinforced laminates. The stiffness can be characterized by flexural and tensile moduli or their derivation. We applied design of experiments (DOE) to achieve our goals, because to solve the existing analytical and numerical models is complicated.We examined the effects of the following parameters: a) composition of reinforce materials (solely carbon, or carbon and glass combination), b) modulus of resin, c) mass ratio of resin-reinforcement, d) order of layers.The samples manufactured on the basis of DOE were investigated mechanically (flexural and tensile moduli measurements) and morphologically (scanning electron microscopy). We compared the measured modulus results to calculated values.

Abstract: The possibilities of the application of microbond test and cylinder tests for determining the interfacial shear strength at the fiber-matrix interface in thermoplastic matrix polymer composites were investigated. Possibilities of test specimen preparation were also investigated. Finally the applicability of the method to make high precision measurement of interfacial shear strength was evaluated.

Abstract: The measurement of thermoelectric power is a powerful method to investigate the metallurgical processes occurring in steels. In this study, four low carbon cold rolled steel sheets having different composition were investigated. The cold rolled sheets were heated up at heating rate 20 °C/hour up to different temperatures, whilst the change of thermoelectric power and hardness have been measured at room temperature after slow cooling. The thermoelectric power of steels increases with temperature until the recrystallization finishes. The raise of thermoelectric power during recrystallization is ranging between 50 and 160 nV/K, depends on the composition of the sheet. Specimens consist of boron exhibit lower thermoelectric power after recrystallization than the steel without any boron, probably due to metastable borocarbide dissolution. This fact could be a good starting point to investigate the effect of boron on thermoelectric power of steels.

Abstract: In this article we dealt with the development of a new method of chemical etching on dental implant materials, Grade 2 and Grade 5 titanium. Certain process creates reproducible homogenous and microrough surface, furthermore improves the reproducibility and productivity for industry appliance. During the research we modified the surface roughness of 2 mm thick samples in a single step of acid etching with a mixture of HF, HNO₃ and distilled water varying the etching time (15-600 seconds). After the surface treatment we obtained the changes of mass and the surface roughness on both sides of every sample. The resulting surface was examined with stereo-and electron microscopy. Based on our results we can determine a parameter setting where the homogenous and microrough surface is reproducible.

Abstract: Durability is one of most important requirements of concrete design. From this aspect is arising the required minimal compressive strength class of conventional concrete in order to ensure durability. The porosity of cement mortar matrix and consequently the liquid and gas permeability of concrete may be reduced. But the strength of lightweight aggregate concrete depends primarily on the crushing resistance of lightweight aggregate (LWA). With low strength LWA may be achieved higher concrete strength by high strength cement mortar matrix. Therefore we can not consider durability simply on the basis of the compressive strength of concrete. The most important durability factors are closely related to the porosity and strength of the cement mortar matrix but for example the abrasion resistance depends more significantly on the aggregate type. Lightweight aggregates usually do not have high abrasion resistance, but they can be advantageous in case of restoration of bridge pavement. The most important factors of durability regarding pavements are frost scaling and abrasion resistance. These parameters (especially abrasion resistance) are not available in the literature when using LWA.

Abstract: The current paper introduces a case study dealing with the problem of pumpability of the ready-mix concrete of grade of C16/20-X0v (H)-24-F3 []. During solving a practical industrial problem we have worked out a modified composition of the related concrete material in order to improve the pumpability. After describing some possible theoretical and practical methods the authors give suggestion for a practical solution. The characteristic feature of the method consists in modifying the recipe of the given grade of concrete without altering the additive structure, and to assure the pulp saturation. The paper reports the results of standardised physical and mechanical tests, executed on the novel concrete material. Based on these results it has been proved, that besides solving the original practical problem of pumpability, the new concrete material possesses better application and technological performance, and is more economical to produce.

Abstract: High quality aluminium matrix syntactic foams (AMSFs) were produced by pressure infiltration. This method can ensure the maximal volume fraction of the reinforcing hollow spheres and very low amount of unwanted or matrix porosities. By this method hybrid MMSFs with mixed metal and ceramic hollow spheres were also produced. The matrix material was AlSi12 alloy and two different types – produced by Hollomet GmbH in Germany – of hollow spheres were used: Globomet (GM) and Globocer (GC). The geometrical properties of the hollow spheres were similar (average outer diameter), but their base material was pure iron and Al₂O₃+SiO₂ in the case of GM and GC hollow spheres respectively. The volume fraction of the reinforcing hollow spheres were maintained at ~65 vol%, but the ratio of them was altered in 20% steps (100% GM + 0% GC, 80% GM + 20% GC...). The results of the compression tests showed, that the compressive strength, yield strength, plateau strength, structural stiffness and the absorbed mechanical energy values increased with higher ceramic hollow sphere reinforcement ratio. The fracture strains of the investigated MMSFs decreased with the higher GC ratio. Generally the strength values also increased with higher diameter to height (H/D) ratio from H/D=1 to H/D=1.5 and 2.

Abstract: The flow zone of the chip in contact with the tool reaches a high temperature in cutting. According to chip hardening experiments α-γ transformation may occur in steel, so the tool is in contact with a high-temperature γ phase at high pressure. The microscopic examination of worn surfaces showed that the degradation of the tool is the result of adhesive/abrasive and thermally activated processes, therefore both friction length and temperature must be taken into consideration in the modelling of crater wear. Wear rate can be described by a non-linear autonomous equation. TiN coating, which increases tool life in high speed steel, changes and slows down the wear of the tool. The activation energy of wear can be calculated from the constants of the wear equation determined by cutting experiments. The deoxidation products to be found in the workpiece in cutting may form a protective layer on the TiN layer that blocks or slows down wear.

Abstract: The aim of this research is to develop a new minimally invasive measurement procedure. With this method implantologist could determine the local mechanical and structural properties of the cellular solids materials (e.g. bones) into which implants are placed. The currently applied methods are based on image measurement procedures (CT, Hounsfield scale etc.). The dentists, with the knowledge of the determined mechanical properties of the bone, can choose the ideal surgical parameters (flap size, diameter of drill, hole-depth, healing time, etc.) and the ideal implant type for the patients. During the development of the measuring procedure, was used bone modeling materials (“bone-like materials”) instead of bone. With these materials it is easier to do tests, than with living tissues. The bone like materials needs to have the same mechanical and structural properties as the given bone. The following bone like materials was used during the measurement: woods (Amaranth, Alnus, Ipe, Iroko, Robinia, Pyrus, Zebrano), and on the market available polyurethane solid foams (Sawbones D1 and D2). Among the literatures are summaries, which include the biomechanical assessments for implant stability. These technics are good to determine the implant stability in different bones and bone like materials after the implantation. In this work torsional test were used. This test is based on the determination of the insertion torque as a function of the implant displacement. Used the insertion torque functions and the screw geometrical parameters, the rotational work was determined. The different materials insertion torque functions have different slope values. The slopes and the rotational work results show which bone like material has similar insertion parameters (insertion torque function, rotational work) as a mandible during the insertion of an implant. With this torsional test and the knowledge of the bone like materials insertion torque functions and the rotational works it is possible to find the best material for the modeling of an implantation. Using this material, medical students can practice and improved the surgical techniques.

Abstract: The AlMgSi1 alloy is generally used in automotive industry owing to its excellent mechanical properties, which can be further improved by applying severe plastic deformation and heat treatment. The dislocation density in the material increases significantly during severe plastic deformation due to the characteristic intensive shear strain. Therefore the motion of dislocations becomes more and more retarded, consequently the strength improves. In addition, the motion of dislocations can be prevented by aging due to formation of coherent precipitations in the metal matrix in order to realize further increasing in strength. In this paper the combined effect of severe plastic deformation and artificial aging treatment on the evolution of mechanical properties was investigated. The samples were subjected to multiple forging (MF) process at room and enhanced temperature. One part of the deformed samples were heat treated at 150°C for different times. The deformed as well as deformed and heat treated samples were investigated by micro hardness testing and X-ray profile analysis.