The investigations were inspired with the problem of cracking of steel castings during the production process. A single mechanism
of decohesion – the intergranular one – occurs in the case of hot cracking, while a variety of structural factors is decisive for hot cracking
initiation, depending on chemical composition of the cast steel. The low-carbon and low-alloyed steel castings crack due to the presence
of the type II sulphides, the cause of cracking of the high-carbon tool cast steels is the net of secondary cementite and/or ledeburite
precipitated along the boundaries of solidified grains. Also the brittle phosphor and carbide eutectics precipitated in the final stage
solidification are responsible for cracking of castings made of Hadfield steel. The examination of mechanical properties at 1050°C
revealed low or very low strength of high-carbon cast steels.
Numerical analysis of the tensioning cables anchorage zone of a bridge superstructure is presented in this paper. It aims to identify why severe concrete cracking occurs during the tensioning process in the vicinity of anchor heads. In order to simulate the tensioning, among others, a so-called local numerical model of a section of the bridge superstructure was created in the Abaqus Finite Element Method (FEM) environment. The model contains all the important elements of the analyzed section of the concrete bridge superstructure, namely concrete, reinforcement and the anchoring system. FEM analyses are performed with the inclusion of both material and geometric nonlinearities. Concrete Damage Plasticity (CDP) constitutive relation from Abaqus is used to describe nonlinear concrete behaviour, which enables analysis of concrete damage and crack propagation. These numerical FEM results are then compared with actual crack patterns, which have been spotted and inventoried at the bridge construction site.
The constant growth of foundry modernization, mechanization and automation is followed with growing requirements for the quality and parameters of both moulding and core sands. Due to this changes it is necessary to widen the requirements for the parameters used for their quality evaluation by widening the testing of the moulding and core sands with the measurement of their resistance to mechanical deformation (further called elasticity). Following article covers measurements of this parameter in chosen moulding and core sands with different types of binders. It focuses on the differences in elasticity, bending strength and type of bond destruction (adhesive/cohesive) between different mixtures, and its connection to the applied bonding agent. Moulding and cores sands on which the most focus is placed on are primarily the self-hardening moulding sands with organic and inorganic binders, belonging to the group of universal applications (used as both moulding and core sands) and mixtures used in cold-box technology.
This paper focuses on mechanical properties of self hardening moulding sands with furfuryl and alkyd binders. Elasticity as a new
parameter of moulding sands is investigated. With the use of presented testing equipment, it is possible to determine force kinetics and
deformation of moulding sand in real time. The need for this kind of study comes from the modern casting industry. New foundries can be
characterized with high intensity of production which is correlated with high level of mechanization and automatization of foundry
processes. The increasingly common use of manipulators in production of moulds and cores can lead to generation of new types of flaws,
caused by breakage in moulds and cores which could occur during mould assembly. Hence it is required that moulds and cores have high
resistance to those kinds of factors, attributing it with the phenomenon of elasticity. The article describes the theoretical basis of this
property, presents methods of measuring and continues earlier research.
In the high-alloy, ferritic - austenitic (duplex) stainless steels high tendency to cracking, mainly hot-is induced by micro segregation
processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier
papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the
chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast
steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated
at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and
low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very
"rich" chemical composition and related with it processes of precipitation of many secondary phases.
Brazing of two dissimilar structural materials; Zircaloy-4 and SS-316L was performed at 900oC under high vacuum conditions. The metallic glass ribbons (Zr55Cu30Al10Ni2Fe3-at. %) of 30 µm thickness, were used as an interlayer. The bonded region was characterized by scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and microhardness testing. The metallurgical bond formation was due to compositional changes in the molten interlayer and later on its subsequent solidification. Assessment of the bonded zone (BZ) revealed three distinct regions (Region-I, Region-II and Region-III). Diffusion transformation was observed in Region-I and Region-III which were interface with base alloys SS-316L and Zircaloy-4 respectively. However, Region-II at the middle of the BZ was composed of isothermally and athermally solidified portions. The highest values of Microhardness were observed in Region-III which was due to the presence of hard phases. Moreover, a crack parallel to BZ was observed in Region-III and was attributed to differential contraction of base alloys during cooling. Maximum shear stress acting on the BZ was calculated and correlated to the brittle phase cracking.
Several previous investigations on failure of a certain type lattice girders railway bridge (on so called BJD line) have not convincingly explained reasons nor have they described potential hazards. This paper attempts to provide an answer, employing static, dynamic, and fatigue analysis of the structure, focusing on previously not analyzed vibrations of elements constituting a lattice node. Detailed models of two types of such nodes – damaged and non- damaged were compared, inside carefully defined limits of applicability.
New approach using direct crack width calculations of the minimum reinforcement in tensile RC elements is presented. Verification involves checking whether the provided reinforcement ensures that the crack width that may result from the thermal-shrinkage effects does not exceed the limit value. The Eurocode provisions were enriched with addendums derived from the German national annex. Three levels of accuracy of the analysis were defined - the higher the level applied, the more significant reduction in the amount of reinforcement required can be achieved. A methodology of determining the minimum reinforcement for crack width control on the example of a RC retaining wall is presented. In the analysis the influence of residual and restraint stresses caused by hydration heat release and shrinkage was considered.
Constantly developing production process and high requirements concerning the quality of glass determine the need for continuous improvement of tools and equipment needed for its production. Such tools like forms, most often made of cast-iron, are characterized by thick wall thickness compared to their overall dimensions and work in difficult conditions such as heating of the surface layer, increase of thermal stresses resulting from the temperature gradient on the wall thickness, occurrence of thermal shock effect, resulting from cyclically changing temperatures during filling and emptying of the mould. There is no best and universal method for assessing how samples subjected to cyclic temperature changes behave. Research on thermal fatigue is a difficult issue, mainly due to the instability of this parameter, which depends on many factors, such as the temperature gradient in which the element works, the type of treatment and the chemical composition of the material. Important parameters for these materials are at high temperature resistance to thermal shock and thermal fatigue what will be presented in this paper.