Controlling of reheated quenching temperature of 1000 MPa grade steel plate for hydropower station

The strength and toughness of 1000 MPa grade steel plate for hydropower station treated by different reheated quenching temperatures were investigated. With the increasing of reheated quenching temperature, the yield strength and tensile strength increase sharply, whereas the value of impact toughness decreases slowly. The lath martensite with high density dislocations enhances dislocation strengthening. On the contrary, the acicular or block ferrite (soft phase) produced by intercritical quenching reduces the phase transformation strengthening. Moreover, the ferrite has a low solubility of interstitial carbon due to the body‐centered‐cubic lattice structure. The bar‐shaped precipitates occur during the isothermal holding at the intercritical temperature and it will reduce the precipitation strengthening. The ferrite phase and high misorientation boundaries are the main factors that contribute to the toughening of the experimental steel. The lower the reheated quenching temperature is, the higher proportion of ferrite and high misorientation boundaries becomes. Considering the requirements for mechanical properties of 1000 MPa grade steel plate for hydropower station, the optimal temperature of reheated quenching is ～920 °C.     

Reliability of masonry walls subjected to in‐plane loading: A slip failure along head joints / Zuverlässigkeit von Mauerwerkswänden bei Belastung in der Ebene: Versagen entlang der Stoßfugenflucht

Masonry structures are a sustainable, economical and traditionally widely used type of construction. However, current masonry design codes are rather conservative, so there is a growing need for revision i.e. calibration of safety factors to improve the allocation of material resources. In this paper, we investigate the probability of occurrence of slip failure along head joints (perpends) in masonry subjected to in‐plane loading. An appropriate limit state function is established and the masonry material properties and loads are defined as random variables in order to simulate likelihood of occurrence of a slip failure regime along the head joints. Furthermore, an example of masonry wall with probabilistic analysis outcomes using Monte Carlo simulation is presented and recommendations for further work are provided.     

Textile reinforcement in the bed joint of basement masonry and infill walls subjected to high wind loads

The successful structural verification of basement walls under earth pressure loading with light vertical loading is often difficult. This situation is often encountered for external basement walls under terrace doors, stairs, masonry light wells, etc., where the vertical loading that is theoretically necessary is absent. This makes it impossible to resist the acting flexural forces from earth using a vertical arch model alone. In such cases the basement wall must also resist the earth pressure in a horizontal direction. However, due to the fact the bending moment capacity of unreinforced masonry parallel to the bed joint is low you have the option here of using a textile‐reinforced bed joint with longitudinal fibres of alkali‐resistant glass or carbon fibre. With an appropriately adapted textile reinforcement in the bed joints, the masonry can fulfil the requirements for load‐bearing capacity against earth pressure with a horizontal load transfer, even under a small vertical load. The same applies to infill walls subjected to high wind loads the bending moment capacities of which are also slightly parallel to and vertically to the bed joint and cannot be provably demonstrated on large infill surfaces and strong wind loads. The load‐bearing can also be increased by improving the flexural strength parallel to the bed joint. The Chair of Structural Design in the Faculty of Architecture of the Technical University (TU) Dresden was carrying out extensive numerical and experimental studies for this purpose. In the journal Mauerwerk 01/2018 [1] first findings from small trial series have already been presented. In the meantime, a series of large‐scale tests have additionally been performed to check the promising results of the small‐scale tests with respect to their real applicability. This report should provide a combined insight into the work of the concluded research project.     

Effect of annealing on the fracture behavior of La0.58Sr0.4Co0.8Fe0.2O3‐δ, a potential energy material for oxygen separation

The perovskite material La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ, offers high oxygen permeability at elevated temperature and is considered as a potential material for oxygen separation membranes. It can enhance the efficiency of oxy‐fuel combustion at high temperatures (> 800 °C) and hence due to the high reliability demands, required by the long term operation at elevated temperatures, it requires a thorough investigation from the view point of structural stability. Aiming towards long term stability, the present work is a detailed and systematic study on the effect of annealing on the mechanical behavior of dense La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ. The study reveals that the indentation fracture toughness of the material increases with increase in annealing temperature. In most of the indentation loads, the subsurface crack profile was Palmqvist in nature with low value of the ratio of crack length versus indentation size (c/a). A consistent pattern of variation of c/a and indentation fracture toughness (K_IC) at all indentation loads was observed. Systematic drop in c/a and subsequent increase in fracture toughness in the as prepared test pieces has been attributed to residual stress accumulation during preparation.     

Determination of the fracture envelope of an adhesive joint as a function of moisture

Adhesive joints in the transportation industry may be exposed to aggressive environments such as humidity during their service life, which may influence their reliability. This research aims to determine the fracture toughness of aluminium bonded joints under pure mode I, pure mode II and mixed mode I and II loadings in dry and wet condition, with the main purpose to predict the influence of humidity in the toughness properties of an adhesive. It was found that water does influence the fracture mechanics properties, increasing mode I fracture toughness and decreasing mode II fracture toughness.     

Effect of welding wire and groove angle on mechanical properties of high strength steel welded joints

Mechanical properties of high strength steel welded joints strictly depend on the welding process, the filler material composition and the welding geometry. This study investigates the effects of using cored and solid welding wires and implementing various groove angles on the mechanical performance of weld joints which were fabricated employing the gas metal arc welding process. It was found that weld joints of low alloy, high strength steels using low alloy steel cored welding wires exhibited higher tensile strength than that of low alloy steel solid wire and chromium‐nickel steel bare welding wire when the method of gas metal arc welding is employed. The effect of groove angle on the strength and toughness of V‐groove and double V‐groove butt‐joints was investigated. V‐groove joints, with higher tensile strength than double V‐groove joints in the whole range of groove angles, were superior in toughness for small groove angles, but impact toughness values of both joints were comparable for large angles. The effect of heat input and cooling rate on the weld microstructure and weld strength was also investigated by performing thermal analysis employing the commercial software ANSYS. It was concluded that cooling rate and solidification growth rate determined the microstructure of the weld zone which had great consequences in regard to mechanical properties.     

Experimental investigations of the environmental effects on stability and integrity of composite sandwich T‐joints

The superior mechanical properties of sandwich composites made them to favored materials, in particular in the aviation industry. However, environmental influences along the manufacturing process and during usage can reduce the strength and the life expectation of the composite parts. This contribution presents an experimental investigation on the effect of accelerated ageing on the mechanical properties of perpendicular honeycomb sandwich connections. Static tensile tests have been carried out on sets of new and 25 days artificially aged specimens and the load carrying capacity of the T‐joints has been measured. In parallel to the experimental part, a three dimensional finite element analysis has been performed. This combined approach allows quantifying the reduction of the fracture toughness of the connections. The obtained results will help to fulfill design requirements and to predict the long‐term structural behavior of sandwich composite constructions.     

Central Bus Station,Kiel: a perforated brick facade for the parking block

On the occasion of the Olympic sailing competitions in Kiel, the ZOB and the multi‐storey car park above it were built in 1972. The two‐storey multi‐storey car park, equipped for about 560 parking spaces, was originally connected to the railway station quay, the main railway station and the city centre by three pedestrian bridges. These bridges were demolished over the years. The new construction of the Atlantic Hotel in 2009 made it necessary to partially demolish the multi‐storey car park and the ZOB. At the same time, preparations began for the redesign of the remaining ZOB site. However, the original idea of renovating the building, which had been reduced in size by the construction of the new hotel, and additionally increasing it by two parking levels, was rejected. The poor structural condition and the planning of a new attractive bus station ultimately required demolition. In the new planning of the ZOB, two construction sites were defined. The design for the new multi‐storey car park on construction site 2 took into account the specifications for the number of storeys, the spacing areas, the maximum eaves height and the materials used in the neighbouring buildings as an independent building. The rounding of the facade at Stresemannplatz gives passers‐by coming from the west a clearer view of the harbour. The spindle, which is raised above the 6th floor, serves as a recognizable point visible from afar.