共查询到20条相似文献，搜索用时 15 毫秒
1.
The increasing amount of ageing civil steel infrastructure requests an enhanced assessment of this infrastructure in terms of determining its residual fatigue life in a more realistic way than this has been done in the past. Often the relevant materials data for cyclic loading of such an ageing infrastructure is not available and its retrieval turns out to be relatively cumbersome bearing the urgency in data availability and continuous cost pressure in mind. This article addresses different approaches and techniques on how materials data for cyclic loading can be obtained at a fraction of the effort compared to state‐of‐the‐art techniques, considering load increase tests, non‐destructive testing techniques and finally even a stepped bar specimen allowing a complete set of materials data (stress‐strain behaviour and stress‐ and strain‐life curve) to be obtained with a single specimen in the end only. Options for ’digitizing’ materials data evaluation are discussed and some prospect on application of those novel approaches and techniques in damage accumulation assessments on real steel infrastructure is provided. 相似文献
2.
3.
M. Thomä A. Gester G. Wagner B. Straß B. Wolter S. Benfer D. K. Gowda W. Fürbeth 《Materialwissenschaft und Werkstofftechnik》2019,50(8):893-912
Friction stir welding as a solid‐state joining method with its comparatively low process temperatures is suitable for joining dissimilar materials like aluminum/magnesium or aluminum/steel. Such hybrid joints are of great interest regarding lightweight efforts in different industrial fields like the transportation area. The present work investigates the influence of additionally transmitted power ultrasound during the friction stir welding on the joint properties of EN AC‐48000/AZ91 and EN AW‐6061/DP600. Therefore, conventional friction stir welding was continuously compared to ultrasound enhanced friction stir welding. Light microscopic analysis and nondestructive testing of the joints using x‐ray and high frequency ultrasound show different morphologies of the nugget for the aluminum/magnesium joints as well as differences in the amount and size of steel particles in the nugget of aluminum/steel joints. Scanning electron microcopy proves differences in the thickness of continuous intermetallic layers for the aluminum/steel joints realized with and without power ultrasound. Regarding the tensile strength of the joints the power ultrasound leads to increased joint strengths for EN AC‐48000/AZ91 joints compared to a decrease for EN AW‐6061/DP600 joints. Corrosion investigations show an influence of the ultrasound power on the corrosion properties of EN AC‐48000/AZ91 joints which is attributed to a changed aluminum content in the nugget region. Because of the great potential difference between the magnesium and the nugget phase the transitional area exhibits strong galvanic corrosion. For EN AW‐6061/DP600 joints an increased corrosion caused by galvanic effects is not expected as the potentials of the EN AW‐6061 aluminum alloy and DP600 steel are very similar. 相似文献
4.
C. Mattheck K. Bethge I. Tesari M. Scherrer O. Kraft 《Materialwissenschaft und Werkstofftechnik》2004,35(9):582-586
Notch stresses are bending stresses due to the deformation of the notch contour line which are superimposed to the nominal stresses. This dual nature of the overall stresses allows to generate an uniform stress state along the notch contour by increasing the superimposed bending stress in the same way as the nominal stress decreases. This was possible till now by CAO (Computer Aided Optimization) [1,2] which simulates tree growth. However a FEM‐program and CAO‐software were necessary. By this deeper understanding of the nature of notch stresses a simple pocket calculator can do the job. Even a pair of compasses and a 45° angle can help. The optimized notch shapes are very similar, so it seems that a universal notch shape might exist under certain circumstances. Fatigue tests by swelling bending proof the success by drastic increase of the number of load cycles until failure. 相似文献
5.
C. R. Sohar A. Betzwar‐Kotas C. Gierl B. Weiss H. Danninger 《Materialwissenschaft und Werkstofftechnik》2008,39(3):248-257
The effect of surface compressive residual stresses (RS) induced by surface grinding and polishing on the gigacycle fatigue behavior of medium‐carbon high‐chromium alloy cold work tool steel was evaluated. Two test series were performed: Specimens of series I revealed high compressive RS of about ‐800 MPa at the surface, resulting from grinding with fine emery paper, which treatment had definitely a beneficial influence on the fatigue endurance strength. The existence of surface RS was also revealed to be responsible for the location of the fatigue crack initiation. High compressive RS favored internal crack origins. In this case crack nucleation sites were primary carbide clusters in the interior of the specimen, forming so‐called fish‐eyes at the fracture surface. In contrast, specimens of test series II had only very low RS, which enabled crack initiation near/at the surface at primary carbides/clusters. Furthermore, it has been shown that the high initial RS are prone to partial relaxation through cyclic loading for which the mechanisms are currently unknown. In this case near‐surface induced failure was obtained. It was possible to confirm the experimentally obtained data by the use of the concept of local fatigue strength as function of effective RS. The relaxation of high initial RS was experimentally confirmed through RS measurements at runout specimens (1010 cycles without failure). 相似文献
6.
D. Krzyżak M. Kurek T. Łagoda D. Sówka 《Materialwissenschaft und Werkstofftechnik》2014,45(11):1018-1029
The paper concerns influence of changes of the bending plane position on the fatigue life. The obtained results were analyzed and compared with the fatigue results for oscillatory bending. The applied specimens were smooth, they had round sections, and they were made of the leaded brass CuZn40Pb2 (MO58). The results obtained under cyclic bending with the plane position change were compared with the results obtained for the specimens with the same parameters under pure oscillatory bending. A change of the bending plane position occurred every 10% fatigue life determined under pure oscillatory bending at the given amplitude of the bending moment, according to the defined fatigue characteristics. Calculated values of nominal stress in a cross section were recalculated according with cyclic material properties and values of elasto‐plastic stress were obtained. 相似文献
7.
Ö. Karakas A. Gülsöz H. Kaufmann C. M. Sonsino 《Materialwissenschaft und Werkstofftechnik》2010,41(2):73-82
In the present study, the results of fatigue tests with the magnesium alloy AZ31 (ISO‐MgAl3Zn1) in the material states base metal, heat affected zone and weld metal obtained under strain control at room temperature within a range from 2·102 to 5·106 cycles are presented. The fatigue behaviour was characterized by the Coffin–Manson–Basquin equations and the stress – strain behaviour by the Ramberg–Osgood equation. The data can be used to assess welded magnesium joints according to the local strain concept. 相似文献
8.
E. Roos T. Gengenbach M. Rauch J. Schemmel 《Materialwissenschaft und Werkstofftechnik》2003,34(9):781-789
Life time assessment on multiaxial cyclic loadings at low and high temperatures For the calculation of fatigue strength of components made out of ductile materials under complex cyclic load different assessments are present. As typical representatives of stress theories the shear stress intensity hypothesis (SIH) as well as the method of critical plane approach (MKS) are considered and compared for rigid and non rigid principle stress directions. Furthermore for synchronous loads the calculation methods are compared with Bach's method. The calculation method becomes more complex, if time dependent material properties at corresponding high temperatures have to be taken into account. In this case the application of viscoplastic material models is necessary, which allows the consideration of combination of creep and fatigue. As an example a modified material model by Chaboche / Nouailhas is used in order to present the calculation of multiaxial creep fatigue tests. 相似文献
9.
《Nondestructive Testing and Evaluation》2012,27(1-6):603-614
Abstract Barkhausen noise is generated by the rapid and irreversible motion of Bloch walls within ferromagnetic materials, when submitted to mechanical stresses or external magnetic field. Bloch walls motion is influenced by obstacles like dislocations, precipitates Therefore Barkhausen noise depends on the microstructure and the stress state of material, that can change during fatigue tests. Indeed the Barkhausen noise measurements can be used as a fatigue damage indicator when the microstructure of the fatigue specimens reaches critical configurations In the present study Barkhausen noise measurements were performed in order to detect the microstructure changes and the initiation of the damage in the case of a cyclic strained industrial steel. The sample is placed in an AC magnetic field to reach saturation. The variations of the magnetic flux within the sample are converted into electric voltage by a surrounding coil transducer. The Barkhausen noise is the high frequency component of this electric signal. The RMS voltage, is used as a quantification of the Barkhausen noise versus the applied field. A maximum in the RMS voltage of the Barkhausen noise is observed. So the RMS voltage appears as a peak shaped curve that we called the Barkhausen peak The influence of the number of cycles and the unloading mode, on the Barkhausen noise, is studied. Fatigue tests are performed according to a push-pull mode under total strain controlled conditions. After the completion of the test, the sample is magnetically characterized. Several cycle numbers (1,10,1000.) were studied to increase the damage. Four unloading modes are used: 2 in traction and 2 in compression (with no unloading plastic strain and from peak stress). The main results of this study are the following: —for given numbers of cycle, the Barkhausen peaks are very different for varying unloading modes. Moreover it is not symmetrical and it is probably depending on the sign of internal stress introduced by cyclic deformation. —for a given unloading mode a progressive boardening of the Barkhausen peak is observed as a function of the cycle number specially for an unloading mode from the tensile peak stress. Moreover a double Barkhausen peak appears from a fatigue level corresponding to approximately one thousand cycles. All these results are analyzed from the microstructural changes by cyclic deformation of the steel specially taking into account the sign and the level of the internal stress field as well as changes in the density of crystal defects, the precipitation state, and the initiation and the development of microcracks Finally characteristics of Barkhausen peaks are proposed as indicators of the fatigue damage (i.e. microcracks initiation). 相似文献
10.
R. Owsiński S. Kamiński M. Szymaniec A. Niesłony T. Łagoda 《Materialwissenschaft und Werkstofftechnik》2015,46(10):1059-1067
The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase. 相似文献
11.
R. Wagener T. Melz C. Fischer M. Matthias H. Kaufmann 《Materialwissenschaft und Werkstofftechnik》2011,42(10):929-933
For the investigation of variable amplitude loading effects, it is necessary to increase the test frequency of conventional testing facilities because, for the evaluation of many components, test results with more than 107 cycles are also needed. However, due to the restriction of conventional testing facilities and the associated costs and required time, variable amplitude testing is almost limited to 107 cycles. Service loading with more than 107 cycles to failure is characterized by low amplitudes with a high number of cycles. The challenge in investigation of material fatigue in the regimes of high cycle and very high cycle fatigue is to apply this large number of cycles to failure in an acceptable time frame. For this reason, it is essential to use a machine, which is able to operate at high frequencies. In this paper, two testing machine concepts with piezo actuators are presented. In the first concept, a high performance piezo stack actuator is presented, in which the specimen and the load cell are mechanically assembled in series. This set‐up applies forces up to 10 kN and testing frequencies up to 1000 Hz. The second testing facility is a hybrid testing system, which consists of an inertial mass actuator and a servo hydraulic actuator connected in parallel. Both systems are capable of testing normal specimen dimensions and provide the possibility to work with variable amplitude loading as well as constant amplitude loading. 相似文献
12.
R. Braun Dr. 《Materialwissenschaft und Werkstofftechnik》2007,38(9):674-689
A short review of the stress corrosion cracking (SCC) behaviour of aluminium alloys is given. Mechanisms of environmentally assisted cracking are outlined. For aluminium alloys, in which stress corrosion cracks propagate predominantly along grain boundaries, anodic dissolution and hydrogen embrittlement have been proposed. Transgranular stress corrosion cracking occurring at severe loading conditions has found particular interest concerning localised corrosion‐deformation interactions. Accelerated test methods for assessing the SCC behaviour are described, including the slow strain rate testing technique and the breaking load method. Results of recent studies on environmentally assisted cracking of aluminium alloys are summarised. Most of the work published in the last two decades has been on aluminium‐lithium based alloys and improved high strength Al‐Zn‐Mg‐Cu alloys in corrosion resistant retrogressed and re‐aged tempers. 相似文献
13.
High cycle fatigue properties of 2124 aluminum alloy plates with different thickness were investigated by determining fatigue S?N curves, fatigue crack growth rates and fracture toughness of 2124‐T851 aluminum alloy plates with the thickness of 30 mm, 40 mm and 55 mm, respectively. Fatigue fracture behaviors of alloy plates were also analyzed and discussed using scanning electron microscope morphology observation, energy spectrum analysis, X‐ray diffraction phase analysis and transmission electron microscopy observation in this paper. The results indicate that plate thickness affects the comprehensive fatigue properties of 2124 aluminum alloy plates. Thinner plate achieves better comprehensive fatigue properties. Due to the different amount of deformation during hot rolling, the variation of microstructure of alloy plates with different thickness mainly concentrates on the difference of grain sizes, substructure and volume fraction of grain boundaries. The thinner the plate, the smaller the grain sizes and therefore the thinner plate produces a higher volume fraction of grain boundaries and substructure, and a greater resistance to fatigue crack growth, thus thinner plate exhibits better fatigue properties. 相似文献
14.
R. Schuller H. Mayer A. Fayard M. Hahn M. Bacher‐Höchst 《Materialwissenschaft und Werkstofftechnik》2013,44(4):282-289
Very high cycle fatigue (VHCF) properties of VDSiCr spring steel are investigated with ultrasonic equipment under fully reversed cyclic torsion loading and under cyclic axial loading at load ratios R = –1, R = 0.1 and R = 0.5. Shot‐peened specimens with surface finish similar to valve springs in combustion engines are tested until limiting lifetimes of 1010 cycles. Under cyclic torsion loading, specimens either fail below 106 cycles with crack initiation at the surface or they do not fail. Under cyclic axial loading, failures above 109 cycles were found for all load ratios with crack initiation at the surface or at internal inclusions. Ratio of mean endurance limit (50% failure probability at 1010 cycles) under fully reversed cyclic torsion and cyclic tension‐compression loading is 0.86. Cyclic torsion loading slightly below the endurance limit leads to cyclic softening first followed by cyclic hardening whereas cyclic stability is found for tension‐compression loading. Cyclic torsion reduces surface compression stresses whereas they are hardly affected by cyclic tension‐compression loading. Mean endurance limit at 1010 cycles for R = 0.1 is 61% of the endurance stress amplitude at load ratio R = –1, and for R = 0.5 it is 44% of the tension‐compression endurance limit. Endurance limits for cyclic torsion and cyclic tension‐compression loading are comparable, if effective stress amplitude is used that considers cyclic normal stresses and residual compression stresses at the surface. 相似文献
15.
T. Sekercioglu 《Materialwissenschaft und Werkstofftechnik》2009,40(9):713-717
The Gerber, modified Goodman, Soderberg, Bagci, ASME‐elliptic and Clemson diagrams are proposed for estimating mechanical element fatigue strength under positive mean and alternating stresses. However, all of these diagrams are either conservative or have fields containing stress greater than yield strength of mechanical element materials. The aim of this study was to propose a new simple diagram with an exponential power k for various types of mechanical element materials. Exponential power k values of steel and Al‐alloy materials were about 0.80 and 0.45, respectively. The proposed diagram (Sekercioglu line) had a minimum average absolute deviation (Xm) of 8.56 %, lower than the Bagci, ASME‐elliptic and Clemson diagrams. The Sekercioglu line can be successfully used in fatigue design processes because of its simple structure and its less conservative nature. 相似文献
16.
Suitability tests on building components and systems Xella produces building materials according to European product standards and European technical approvals, respectively. Products of a new type or manufactured with a new raw material undergo an internal release process in which the requirements coming from standards, approvals and supplementary national application documents are proved. In addition, the interaction of the Xella building materials with further products applied on construction site are tested. This includes systems like masonry, external thermal insulation composite systems (ETICS), rendering systems, large‐format reinforced components, structures with fixing elements and much more. The scope of the system tests is determined by the intended application and by Xella internal requirements which, in many points, exceed the sets of rules. This article demonstrates the spectrum of these tests and, using the example of the render and mortar tests, the principle of the internal test guidelines. 相似文献
17.
Dr. rer. nat. Herbert Wiggenhauser Matthias Behrens Dipl.‐Ing. Dr. rer. nat Dorothee Moser Ralf M. Moryson Dipl.‐Ing. Dr.‐Ing. Sergey Pudovikov Prof. Dr.‐Ing. Hans‐Georg Herrmann 《Mauerwerk》2018,22(3):175-186
A large retaining wall (appr. 9 m high and 286 m long) of a former coal mine has been investigated using Ground Penetrating Radar (GPR), with two low frequency antennas (200 and 400 MHz), and Large Aperture UltraSound (LAUS) to gather information about the condition and inner structure of the wall. Three vertical lines were selected in representative areas of the wall to evaluate the usefulness of Non‐Destructive Testing (NDT) with these two methods. The LAUS results showed the layer structure at one line where the wall was enforced by a concrete shell and were unspecific regarding the inner structure beyond the first layer. GPR results were able to be collected much faster and showed some internal features. Penetration was limited to 2–3 m due to the high absorption in the material. 相似文献
18.
Service load is often a non‐proportional multi‐axial load. The result of operation of such type of load on constructional elements is the decrease of fatigue lives in relation to proportional load of the same equivalent value. There are many damage models for non‐proportional fatigue, however, none of them obtained general acceptance. The key issue for creation of correct damage model is the selection of appropriate load parameters. The article presents methodology of obtaining cumulative exceeding histogram (load spectrum) containing key parameters of non‐proportional load. The hereby work includes: proposal of method of forming of block load spectrum for non‐proportional load, example block load programs for various types of multi‐axial load and results of experimental tests of fatigue lives obtained on the basis of formulated programs. 相似文献
19.
H. Schuermann 《Materialwissenschaft und Werkstofftechnik》2011,42(10):942-949
Mechanisms are presented which occur in unidirectional fiber reinforced plastics due to fiber fracture and subsequent crack evolution. The 3‐point‐bending test was chosen as test method and the analyses are predominantly carried out by microscopy. It is shown that the matrix system, the fiber‐matrix interface adhesion strength and the fiber volume fraction are of great importance for improving fatigue strength. The results can be transferred directly to high stressed bending structures such as leaf springs. 相似文献