Experimental analysis of the effect of in-plane strain path changes and Bauschinger effects during mechanical loading that involves compression is quite challenging for sheet materials because they are prone to buckling. In this contribution, we present a newly developed method that allows to deform sheet metals both in tension and in compression. Our experimental setup primarily consists of an anti-buckling clamping device that can be used in a universal mechanical testing machine. Surface strains are measured with a Digital Image Correlation (DIC) system. To demonstrate the viability of our method, first tests are conducted on thin sheet specimens (1 mm thickness) of a DC06 steel. Several approaches to reduce friction between the clamping system and the specimen are investigated. The validity of the test results is established in monotonic tensile tests. Measurements with different amounts of pre-strain and different reversed strain values are also discussed, showing that DC06 exhibits a Bauschinger effect that can be further quantified using different Bauschinger parameters.
The principle of the active thermography is based on the evaluation of a previously excited heat flow in tested material and its disturbance by hidden defects and cracks. High sensitive and fast thermography camera follows a mathematical analysis to extract reliable defect detection information. This is an efficient method for rapid inspection of large areas of tested objects in non-contact and non-destructive way.
With a different kind of excitation method there is a huge possible application for testing. Optically excited lock-in thermography allows inspection of large areas with complex structures in one go. Pulsed (phase) excited lock-in thermography is characterized by extremely short test duration and high detection sensitivity. These methods are used for CFRP in aerospace or automotive industry. Induction thermography is used for the quality assessment of the joint connections both in the production environment and in the maintenance. At the same time induction thermography is suitable for crack detection and welding/soldering inspection. Ultrasound lock-in thermography is then a method for defect selective indication of cracks, disbonds or delaminations. Finally the laser excited thermography is a non-contact method which is ideally suited for the characterization of joints, welds, thin films and coatings. The Fourier evaluation technique allows to get the precise determination of thickness, porosity or temperature conductivity.
Many of active thermography excitation sources can be used for many applications in correlation of needs and demands. Often depends on appropriate thermal camera, its type of detector (technology, sensitivity, frame rate) and suitable software module for the whole system.
The paper is dealing with strain controlled cyclic deformation using a non-contact strain measurement based on digital image correlation techniques on proportional sizes of conventional specimens. The cyclic behaviour of 34CrNiMo6 high-strength steel was investigated on round shape specimens in accordance with ASTM E606 standards and compared with miniaturized specimens up to 1.5mm in diameter with the cycle asymmetry coefficient R=-1. This application is intended to be used for life time assessment of in service components in future work which enables to carried out a group of mechanical tests from a limited amount of the experimental material. The attention was paid to confirm the suitability of the proposed size miniaturization geometry. The test results obtained enabled to construct Manson-Coffin curves and assess fatigue parameters. The purpose of this study is to present differences between cyclic curves and cyclic parameters which have been evaluated based on conventional and miniaturized specimens.
Anisotropy of fuel claddings of Fe-9Cr and Fe-14Cr ODS (oxide dispersion-strengthened) steel for Generation IV reactors with coolants based on liquid metals was examined. Basic mechanical tests were performed at temperatures 300, 500 and 625°C on ODS steel thin wall tubes. Tensile tests were performed in axial and tangential direction, both in vacuum to avoid the oxidation of the small specimens. As a testing machine was used the scanning electron microscope with small in-situ tensile testing device.
Application of the mini samples method is very common especially for residual life assessment of the components operating in the energy sector. Residual lifetime estimation and early detection of possible risks of mechanical equipment failure and structures is a key question for reliable operation in industrial plants. Currently, this issue is particularly critical in power stations and petrochemical plants that are approaching their design lifetime. Throughout the operation, the various degradation processes may cause deterioration of the mechanical properties of the operating components. Residual lifetime of operating device can be evaluated using standard tests, but usually cannot be extracted from the components
enough of material. It is possible to use a semi destructive sampling of materials and test methods with miniature specimens. This article deals with comparison of the creep results performed on standard test bars and sub size samples of the type Small Punch Test and new proposed miniature samples with dimension in the measured part 4x1,2-13mm which were loaded with a conventional uniaxial creep tests. The experiment was performed on steam line material 15 128 after operation. The results were obtained from 16 standard creep test, 10 Small Punch Test and 8 results using mini samples. Emphasis was put to practical use of the test results and therefore residual life was determined 798 h by standard test and 661 h using the mini samples. The results obtained for standard and mini samples exhibit very good agreement. The SPT results evaluated two base of available correlation for the material investigated yield significantly different values. This final service life evaluated not performed with the use of these specimens.
Tests of candidate construction materials for heavy liquid metal environment are performed with support of project Sustainable energy (SUSEN) and in cooperation with other European partners in frame of MATISSE project. Attention of CVR is besides other things focused on influence of corrosion environment on mechanical properties of T91 steel. Non-standard environment requires special testing device which must be able to perform tests in liquid lead or liquid lead bismuth eutectic. Not negligible issue is also monitoring of oxygen volume which has an influence on production and stability of oxide layers and therefore on crack initiation.
Characterisation of engineering materials and components is a crucial part for design and save service life utilization. Due to components processing technologies and exploitation conditions local properties can significantly vary from location to location over larger components as well as over small material volumes with gradual material changes such as welds, coatings or additively manufacture parts. The current paper is dealing with local properties characterisation for additively manufacture (AM) components by micro tensile test (M-TT). Components produced by additive manufacturing techniques yield properties variation in dependence of the considered location within the component regarding to direction in relation to deposition process. Properties vary over the thickness, length, angle or contacts with the supporting structures necessary for a successful components production by additive manufacturing techniques. The properties differences are mainly related to varying heating/reheating and cooling conditions at various locations of usually very complex parts produced mainly by these technologies. The standard testing procedures fail to characterize such local properties of complex shaped objects due to large size requirements on specimens. Therefore, new techniques have to be established for such detailed local characterizations. Results of miniaturized tensile tests application for local properties and orientations are shown here.
This contribution is based on the experimental programme which deals with the issue of blade steel T552 corrosion fatigue damage. The specimens were taken from a reference material delivered for blade production and tested in the corrosion cell under pre-stress of 300 MPa. The chloride solution of 35 ppm was chosen as the environment at the temperature of 80°C. Such an environment can be considered as the limit state that should not occur during the operating regime. The results were compared with previous experiments and the conclusions were summarized.
Absorbed energy obtained from impact Charpy tests is one of the most important values in many applications, for example in residual lifetime assessment of components in service. Minimal absorbed energy is often the value crucial for extending components service life, e.g. turbines, boilers and steam lines. Using a portable electric discharge sampling equipment (EDSE), it is possible to sample experimental material non-destructively and subsequently produce mini-Charpy specimens. This paper presents a new approach in correlation from sub-size to standard Charpy test results.
The article presents the results of the evaluation of tribological properties of modified surfaces of steel samples. Comparing the effect of surface modification on the friction coefficient and wear resistance enabling optimization of surface modifications for various applications.
Titanium is a material that exhibits many desirable properties including a very high strength to weight ratio and corrosive resistance. However, the specific properties of any components depend upon the microstructure of the material which varies by the manufacturing process. This means it is often necessary to analyse the microstructure when designing new processes or for performing quality assurance on manufactured parts. For titanium alloys, this analysis is typically performed manually by expert materials scientists since the complicated microstructure of the material means no existing software is capable of reliably identifying the grain boundaries. This manual process is time consuming and offers low repeatability due to human error and subjectivity. In this paper, we propose a new, automated method to segment microstructural images of a Ti6Al4v alloy into its constituent grains and produce measurements of the grains. The results of applying this technique are evaluated by comparing the measurements obtained by the proposed approach to those produced by various experts performing the manual process. By repeating the manual segmentation a number of times with different operators working under different time constraints we also explore the reliability of the manual process and contrast this with improvements offered by our approach.
Abstract. There are many cases when there is a shortage of the experimental material for detailed analysis and then small size specimens techniques becomes essential. The current paper deals with investigations of mini-tensile tests (MTT) application to metal sheets characterization. In the case of metal sheets assessment the most common are tensile tests for Lankford parameters and strain hardening determination. As most of the processes are not quasi-static and constant strain rate processes, thus assessment of strain rate hardening is also crucial part of the characterization. Previously developed and verified testing procedure of M-TTs for bulk materials is applied here for steel sheet made of DC01 characterization. Tests under quasi-static and dynamic loading conditions are carried out in order to describe above mentioned properties at room temperature. Accurate strain measurement is carried out with digital image correlation systems and results obtained with M-TTs are going to be confronted with standard size specimens’ results.
Fracture toughness cannot be readily measured in metal sheets because its limited thickness (1-3 mm) does not allow to fulfill the plain strain conditions required to apply ASTM standard procedures. In such cases fracture toughness can be estimated through the application of the Essential Work of Fracture (EWF) methodology. Many studies carried out at CTM have demonstrate the applicability of the EWF methodology to Advance High Strength Steels (AHSS) sheets. Fracture toughness is a relevant parameter to consider in such steels, which are more sensitive to edge cracking because their high strength and limited ductility. Cracks tend to appear during forming operations, like punching or trimming. Thus, the stretch-flangeability of these steels is mainly governed by the propagation of such cracks. Fracture toughness is the property that control the crack propagation in a material, so, it could be used to rationalize and foresee the stretch flangeability in AHSS. The fracture toughness of several AHSS grades has been studied at CTM by the EWF methodology and results have been related to the stretch-flangeability, measured in terms of Hole Expansion Ratio (HER). Results show a good trend between fracture toughness and stretch-flangeability, i.e. the tougher the steel is, the higher HER it presents.
Sometime stress-strain curves at elevated temperatures are measured on small specimens due to lack of material for producing specimens of standard size. Here is meant the lack because contemplated savings or due to instability of tested state of material in a sufficiently large volume during a period long enough. Engineers must be interested in deviation between data from standard and non-standard tests. A comparative experiment was carried out on stainless steel 304/4301 at 660°C and strain rate of 1 s-1.