Papers by Keyword: Creep Behaviour

Abstract: The mechanical behaviors of Nylon6 polymer film material are investigated experimentally. A technique, marker identification method, for non-contact optical measurement of in-plane displacements based on correlation analysis is employed to measure the deformation of the film specimens. Based on the uniaxial tension experimental results, the stress-strain relationship is obtained, which result in Young’s modulus and the Poisson’s ratio. In the creep experiment, the time-depending response of polymer film material is studied. The strain state is determined by measuring the deformations over time. Based on the obtained data about the material’s response, the bulk-modulus K(t) is calculated based on BOLTZMANN’s superposition principle.

Abstract: A 9-12% Cr ferritic steel weld metal containing 1% Co partially substituted for nickel was prepared by submerged arc welding processing(SAW). The microstructures and creep properties of the weld metal have been investigated. The microstructure exhibited a fully tempered martensitic structure free of δ-ferrite. The creep properties of the obtained weld metal are inferior to that of the P92 base metal at 600 and 650 . The values of A and n for weld metal in Norton power law constitution at 650 are 1.12×10-21 and 8.14, respectively.

Abstract: An investigation has been made into the microstructure and creep behaviors of [110] oriented single crystal nickel-base superalloy. Results show that, after a full heat treated, the cubic  phase is coherently embedded in the matrix and regularly arranged along the <100> orientation. During creep, the cubic phase in the alloy is transformed into the rafted structure lying 45 relative to the direction of the applied stress. Under the condition of the applied stress of 137 MPa at 1040°C, the alloy displays a higher strain rate and shorter creep lifetime. The deformation mode of the alloy during creep is dislocations activated within the matrix channels and the rafted phase. Dislocation slip activated easily on the Roof-type channel is thought to be the main reason of the alloy having higher strain rate and shorter creep lifetime.

Abstract: For the production of endless glass fibres, the use of glass fibre bushings made of PtRh alloys is necessary. The manufacturing process for high melting glass fibres in particular leads to simultaneous chemical attack and mechanical loading at extremely high temperatures.The influence of these complex loadings on the stress-rupture strength and the creep behaviour of various PtRh alloys (conventional and oxide dispersion strengthened alloys) was investigated after contact with various glass melts. The investigations include both long-term tests under service conditions and laboratory corrosion tests. The investigations will be complemented with metallographic and fracture examinations in the SEM and microprobe analysis.Furthermore, the fibre manufacturing process is influenced by the wetting of the bushing material by the glass melt. For this reason the wetting behaviour of the platinum materials in contact with the different glass melts was investigated as a function of the working temperature of the glass fibre bushings. The results of the investigations provide a basis to optimise materials selection for glass fibre bushings.

Abstract: An experimental analysis on a set of strengthened masonry walls has been carried out by means of cyclic loading tests in order to simulate the creep effects. The damage evolution of specimens reinforced by traditional or innovative methods is evaluated by the Acoustic Emission (AE) technique. The AE time dependence during fracture propagation is analysed through a power law. In addition, the AE frequency analysis is used to obtain information on the criticality of the ongoing process.

Abstract: Present paper deals with the delayed fracture in woven GFRP underwater at elevated temperature. The tensile test of GFRP after water immersion was conducted to evaluate the residual strength ater immersion at various water temperatures. The residual strength of GFRP decreased with the increase in the water temperature and the immersion time. In fact, the transition in failure mode with water immersion was ascertained from SEM observation of the fracture surface. Additionally, creep test in air and under hot water at 95°C was conducted. The creep rupture time decreased drastically with water immersion, in contrast, creep rupture wasn’t observed from the creep test in air. It was clarified that the water immersion generated the transition in the failure mode of GFRP and therefore led to the acceleration of the strength degradation.

Abstract: Magnesium alloys had gained an increasing interest in recent years due to their promising property profile for light weight constructions. They offer drastic advantages in weight reductions in automotive industries compared to steel or even aluminium. Therefore they can be used to decrease the emission of green house gases as requested by the EU directive for the reduction of CO2 emissions and moreover due to their recyclability they also help to fulfill the requirements from the EU directive regarding the end of life of vehicles. But still there are some limitations with regard to strength, mostly at elevated temperatures above 130 °C. To overcome these limitations alloy development as well as process optimization has to be done for further enhancement of the range of magnesium applications. This paper will show and discuss the property profiles of the standard magnesium alloy AZ91D compared to the recently developed, heat resistant magnesium alloy MRI153. The alloys have been processed using normal high pressure die casting (HPDC), New Rheocasting (NRC) and Thixomolding® (TM). As methods of investigation tensile and creep tests have been applied. The creep properties have been determined in the temperature range of 135-150 °C and loads of 50-85 MPa. All these trials have been accompanied by metallographic observations (light optical metallography, SEM) and density measurements to investigate the influence of the processing routes on microstructure and the porosity of the materials. It will be shown that the differences in the property profile of the chosen alloys are dependent on their different chemical compositions as well as on different microstructures that are obtained by the different processing routes. While in the case of AZ91D, TM is showing advantages compared to HPDC for room temperature applications, the NRC in combination with the heat resistant alloy leads to an improvement of creep rates by two orders of magnitudes.

Abstract: Critical high temperature components of machines and structures are often subjected to complicated load and temperature histories. The closest laboratory simulation of service loading conditions involves creep under nonsteady temperatures and stresses. For example, the start up and shut down cycles can be well simulated by temperature variation by use of intermittent heating tests. Such approach is illustrated by recent experimental results on advanced high creep strength 9- 12%Cr ferritic-martensitic steels (P91, P92 and E911). A comparison between the creep characteristics of nonsteady and monotonously creep specimens has revealed no significant deterioration of the creep strength and fracture resistance of these steels in power-law (dislocation) creep.

Abstract: Creep property of solder alloys is one of the important factors to effect the reliability of surface mount technology (SMT) soldered joints. The creep behavior and its rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints were separately investigated and predicted under constant temperature by a single shear lap creep specimen with a 1mm2 cross sectional area and finite element method (FEM) in this paper. Results show that the creep property of Sn2.5Ag0.7Cu0.1RE is superior to that of the commercial employed lead-free solder Sn3.8Ag0.7Cu and the creep rupture life of its soldered joints is 8.4 times more than that of Sn2.5Ag0.7Cu solder. The creep rupture life of Sn2.5Ag0.7CuXRE lead-free soldered joints indirectly predicted by FEM is better in accord with that of actual testing results, which are important to design the reliability of lead-free soldered joints for SMT.

Abstract: This paper examines the effect of equal-channel angular pressing (ECAP) on creep behaviour of pure aluminium, binary Al-0.2wt.%Sc alloy and ternary Al-3wt.%Mg-0.2wt.%Sc alloy. The ECAP was conducted at room temperature with a die that had a 90° angle between the channels and 8 repetitive ECAP passes followed route BC. Constant stress compression creep tests were performed at 473 K and stresses ranging between 16 to 80 MPa on ECAP materials and, for comparison purposes, on the initial coarse-grained materials. The results showed that the creep resistance of the ECAP processed Al-Sc and Al-Mg-Sc alloys was markedly deteriorated with respect to unpressed coarse-grained materials.