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Number of results: 82
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Abstract

As a machining technology, welding can cause serious accidents by overloading or operation mistakes. Through analyzing the causes of various welding accidents, we found that the major cause for damage imposed after welding parts are loaded is the fracture of materials. Therefore, studying the influence of welding residual stress on the fracture property of materials is of great significance. This paper applied the digital image correlation technique to study the fracture property of welding parts under the influence of welding residual stress. In addition, standard parts and welding parts were selected to carry out a contrast experiment. Room temperature tensile tests were performed on both standard parts and test pieces after residual stress measurement. Using displacement field and strain field data obtained through VIC-2D software, the stress intensity factor around the crack tip of each specimen under the conditions of small load was calculated and corresponding analysis was carried out.

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Authors and Affiliations

J. Bian
Zx. Ge
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Abstract

The small artificial surface defects in the coarse-grain steel are studied. The size of the used defects is smaller than the most relevant microstructural unit of steel, i.e. the average grain size. The samples of coarse-grain steel are prepared using a welding thermal-cycle simulator and a laboratory furnace. The defects are made by indenting with a Vickers pyramid. One of the final results of the defect making is the existence of local residual stresses. The influence of residual stresses on the crack initiation from those artificial defects is discussed in the article.

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Authors and Affiliations

Vladimir Gliha
Volodymyr Hutsaylyuk
Lucjan Śnieżek
Tomaz Vuherer
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Abstract

The usefulness of elastic compliance measurements to estimate crack closure in structural steel and the validity of the assumption of a constant compliance value for the fully open crack is examined. Based on considering different issues related to the experimental technique and compliance data processing, local compliance measurements and the compliance offset method recommended by the ASTM standard are selected to be most suitable for structural steel. The compliance data generated in fatigue tests on I 8G2A steel conducted under a variety of loading conditions enabled to choose an optimal strain gauge positioning and appropriate offset criterion values for the original compliance offset method and its modified (normalized) version. The adequacy of the closure measurements is assessed through checking the ability of the resulting effective stress intensity factors to account for the observed effects of the loading conditions on fatigue crack growth rates.
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Authors and Affiliations

Małgorzata Skorupa
Andrzej Skorupa
Tomasz Machniewicz
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Abstract

Effects of specimen thickness and stress ratio on fatigue crack growth and crack closure levels under constant amplitude loading and after a single overload have been studied experimentally for a structural steel ( I 8G2A). The corresponding crack growth data from the fatigue tests have been presented and evaluated. The experimental trends have been compared to those reported in the literature for various steels. The ability of the effective stress intensity factor range based on crack closure measurements to correlate the observed crack growth response has been investigated.
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Authors and Affiliations

Małgorzata Skorupa
Andrzej Skorupa
Jaap Schijve
Tomasz Machniewicz
Paweł Korbut
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Abstract

This study was carried out on the background of Sutong Bridge project based on fracture mechanics, aiming at analyzing the growth mechanism of fatigue cracks of a bridge under the load of vehicles. Stress intensity factor (SIF) can be calculated by various methods. Three steel plates with different kinds of cracks were taken as the samples in this study. With the combination of finite element analysis software ABAQUS and the J integral method, SIF values of the samples were calculated. After that, the extended finite element method in the simulation of fatigue crack growth was introduced, and the simulation of crack growth paths under different external loads was analyzed. At last, we took a partial model from the Sutong Bridge and supposed its two dangerous parts already had fine cracks; then simulative vehicle load was added onto the U-rib to predict crack growth paths using the extended finite element method.

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Authors and Affiliations

H. Zhu
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Abstract

In this paper the effect of soldering technique and thermal shock test were investigated on SAC 305 solder joints, produced by two different solder method. The solder joints were subjected to different cycle numbers up to 5000 thermal shock tests with two different thermal profiles of –30/+110°C and –40/+125°C. Microstructural properties of the tested joints were examined with the focus on intermetallic layer thickness and crack formation/propagation. Thickness of the scallop shaped Cu6Sn5 intermetallic layer was increased with increasing cycle number for both THRS and multiwave joints, but the thickening was more effective for the THRS joints. Cracks typically formed at the solder alloy/ PTH barrel and the solder alloy/pin interfaces and propagated along grain boundaries and precipitations of intermetallic compound.

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Authors and Affiliations

D. Koncz-Horváth
G. Gergely
Z. Gyökér
Z. Gácsi
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Abstract

An automated method for crack identification and quantitative description of crack systems in concrete was developed in order to aid a service life assessment of concrete elements in structures. Flat polished specimens for crack analysis were impregnated with epoxy resin containing fluorescent dye. The examination of the crack system was performed in ultraviolet light using a stereomicroscope and an Image Pro Plus image analysis system on specimens cored out of several concrete structures. The laboratory tests were performed on cast specimens to establish correlations between water penetration and chloride diffusion and crack system parameters. The analysis of cracks in concrete cores taken from structures resulted in interesting conclusions based on the crack width distribution and crack localization with respect to steel reinforcement. The method was found very effective to support standard concrete diagnostics methods.

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Authors and Affiliations

M.A. Glinicki
A. Litorowicz
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Abstract

In the paper, the method of a numerical simulation concerning diagonal crack propagation in con-crete beams was presented. Two beams reinforced longitudinally but without shear reinforcement were considered during the Finite Element Method analysis. In particular, a nonlinear method was used to simulate the crack evaluation in the beams. The analysis was performed using the commercial program ANSYS. In the numerical simulation, the limit surface for concrete described by Willam and Warnke was applied to model the failure of concrete. To solve the FEM-system of equations, the Newton-Raphson method was used. As the results of FEM calculations, the trajectories of total stains and numerical images of smeared cracks were obtained for two analyzed beams: the slender beam S5 of leff = 1.8 m and the short beam S3k of leff = 1.1 m. The applied method allowed to generate both flexural vertical cracks and diagonal cracks in the shear regions. Some differences in the evaluation of crack patterns in the beams were observed. The greater number of flexural vertical cracks which penetrated deeper in the beam S5 caused the lower stiffness and the greater deformation in the beam S5 compared to the short beam S3k. Numerical results were compared with the experimental data from the early tests performed by Słowik [3]. The numerical simulation yielded very similar results as the experiments and it confirmed that the character of failure process altered according to the effective length of the member. The proposed numerical procedure was successfully verified and it can be suitable for numerical analyses of diagonal crack propagation in concrete beams.

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Authors and Affiliations

M. Słowik
P. Smarzewski
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Abstract

In the present work, an experimental investigation of a transverse fatigue crack has been carried out. A mathematical modelling of cracked rotor system along with the measured vibration is used to find crack parameters that not only detect the fault but also quantify it. Many experimental studies on cracks considered the crack as a slit or notch, which remains open. However, such flaws do not mimic a fatigue crack behavior, in which crack front opens and closes (i.e., breathes in a single revolution of the rotor). The fatigue crack in rotors commonly depicts 2x frequency component in the response, as well as higher frequency components, such as 3x, 4x and so on. In rotors, both forward and backward whirling take place due to asymmetry in rotor, and thus the fatigue crack gives the forward and backward whirl for all such harmonics. A rotor test rig was developed with a fatigue crack in it; rotor motions in two orthogonal directions were captured from the rig at discrete rotor angular speeds using proximity probes. The directional-spectrum processing technique has been utilized to the measured displacements to get its forward and backward whirl components. Subsequently, it is executed in a mathematical model-based estimation procedure to obtain the crack forces, residual unbalances, and remaining rotor system unknown variables. Estimation of crack forces during rotation of the shaft gives its characteristics, which can be used further to develop newer crack models.

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Bibliography

[1] Y. Ishida. Cracked rotors: Industrial machine case histories and nonlinear effects shown by a simple Jeffcott rotor. Mechanical Systems and Signal Processing, 22(4):805–817, 2008. doi: 10.1016/j.ymssp.2007.11.005.
[2] G. Sabnavis, R.G. Kirk, M. Kasarda, and D. Quinn. Cracked shaft detection and diagnostics: a literature review. The Shock and Vibration Digest, 36(4):287–296, 2004. doi: 10.1177/0583102404045439.
[3] N. Dharmaraju, R.Tiwari, and S. Talukdar. Identification of an open crack model in a beam based on force-response measurements. Computers & Structures, 82(2-3):167–179, 2003. doi: 10.1016/j.compstruc.2003.10.006.
[4] A.S. Sekhar. Crack identification in a rotor system: a model-based approach. Journal of Sound and Vibration, 270(4-5):887–902, 2004. doi: 10.1016/S0022-460X(03)00637-0.
[5] A.C. Chaselevris and C.A. Papodopoulos. Experimental detection of an early developed crack in rotor-bearing system using an AMB. Third International Conference of Engineering against Failure, June 26–28, 2013, Kos, Greece.
[6] P. Gudmundson. The dynamic behaviour of slender structures with cross-sectional cracks. Journal of the Mechanics and Physics of Solids, 31(4):329–345, 1983. doi: 10.1016/0022-5096(83)90003-0.
[7] C.A. Papadopoulos and A.D. Dimarogonas. Stability of the cracked rotors in the coupled vibration mode. Journal of Vibration, Acoustics, Stress, and Reliability in Design, 110(3):356–359, 1988.
[8] A.K. Darpe, K. Gupta, and A. Chawla. Experimental investigations of the response of a cracked rotor to periodic axial excitation. Journal of Sound and Vibration, 260(2):265–286, 2003. doi: 10.1016/S0022-460X(02)00944-6.
[9] T. Zhou, Z. Sun, J. Xu, andW. Han. Experimental analysis of cracked rotor. Journal of Dynamic systems, Measurement, and Control, 127(3):313–320, 2005. doi: 10.1115/1.1978908.
[10] P. Pennacchi, N. Bachschmid, and A. Vania. A model-based identification method of transverse cracks in rotating shafts suitable for industrial machines. Mechanical Systems and Signal Processing, 20(8):2112–2147, 2006. doi: .
[11] J.K. Sinha. Higher order spectra for crack and misalignment identification in the shaft of a rotating machine. Structural Health Monitoring, 6(4):325–334, 2007. doi: 10.1177/1475921707082309.
[12] Z. Cai. Vibration diagnostics of elastic shafts with a transverse crack. Master Thesis, Faculty of Computing, Health and Science, Edith Cowan University, Perth, Australia 2011.
[13] S.K. Singh and R. Tiwari. Detection and localization of multiple cracks in a shaft system: An experimental investigation. Measurement, 53:182–193, 2014. doi: 10.1016/j.measurement.2014.03.028.
[14] D. Southwick. Using full spectrum plots: Part 2. Orbit, 15(2):10–16. 1994.
[15] P. Goldman and A. Muszynska. Application of full spectrum to rotating machinery diagnostics. Orbit, 17–21, 1999.
[16] J. Tuma, and J. Bilos. Fluid induced instability of rotor systems with journal bearings. Engineering Mechanics, 14(1-2):69–80, 2007.
[17] T.H. Patel and A.K. Darpe. Application of full spectrum analysis for rotor fault diagnosis. In: IUTAM Symposium on Emerging Trends in Rotor Dynamics, 1011:535–545, 2011.
[18] C. Shravankumar and R. Tiwari. Detection of fatigue crack in a rotor system using full-spectrum based estimation. Sadhana, 41(2):239–251, 2016. doi: 10.1007/s12046-015-0452-9.
[19] C. Shravankumar and R. Tiwari. Model-based crack identification using full-spectrum. In Proceedings of the ASME 2013 Gas Turbine India Conference, Bangalore, Karnataka, India, December 5–6, 2013. doi: 10.1115/GTINDIA2013-3756.
[20] C. Shravankumar and R. Tiwari. Identification of stiffness and periodic breathing forces of a transverse switching crack in a Laval rotor. Fatigue and Fracture of Engineering Materials and Structures, 36(3):254–269, 2012. doi: 10.1111/j.1460-2695.2012.01718.x.
[21] C. Shravankumar, R. Tiwari, and A. Mahibalan. Experimental identification of rotor crack forces. In: Proceedings of the 9th IFToMM International Conference on Rotor Dynamics: pp. 361–371, 2015. doi: 10.1007/978-3-319-06590-8_28.
[22] X.B. Rao, Y.D. Chu, Y.X. Chang, J.G. Zhang, and Y.P. Tian. Dynamics of a cracked rotor system with oil-film force in parameter space. Nonlinear Dynamics, 88(4):2347–2357, 2017. doi: 10.1007/s11071-017-3381-9.
[23] B.C. Wen and Y.B.Wang. Theoretical research, calculation and experiments of cracked shaft dynamical responses. In Proceedings of International Conference on Vibration in Rotating Machinery, pp. 473–478, London, UK, 1988.
[24] Prashant Kumar. Elements of Fracture Mechanics. Wheeler Publishing, New Delhi, 1999.
[25] M.G. Maalouf. Slow-speed: vibration signal analysis. Orbit, 27(2):4–16, 2007.
[26] R. Tiwari. Rotor Systems: Analysis and Identification. CRC Press, USA, 2017. doi: 10.1201/9781315230962.
[27] L.G.G. Villani, S. da Siva, and A. Cunha Jr. Damage detection in uncertain nonlinear systems based on stochastic Volterra series. Mechanical Systems and Signal Processing, 125:288–310, 2019. doi: 10.1016/j.ymssp.2018.07.028.
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Authors and Affiliations

C. Shravankumar
1
Rajiv Tiwari
1

  1. Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781039, India.
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Abstract

The numerical solutions of stress and strain components on the critical plane of tungsten carbide coating were solved based on the critical plane method in three-dimensional coordinate system, and accordingly three strain energy density parameters (Smith-Watson-Topper, Nita-Ogatta-Kuwabara and Chen parameters) were determined to reveal the fretting fatigue characteristics of tungsten carbide coating. In order to predict the fretting fatigue life based on the strain energy density criterion, the expressions between the strain energy density parameter and the fretting fatigue life was obtained experimentally. After the comparison of the three strain energy parameters, it was found that all three parameters could accurately predict the crack initiation position, but only the Smith-Watson-Topper parameters could accurately predict the crack initiation angle. The effects of cyclic load, normal load and friction coefficient on fretting fatigue damage behaviors were discussed by using the Smith-Watson-Topper criterion. The results show that the fretting fatigue life decreases with the increase of cyclic load; an increase in the normal contact load will cause the Smith-Watson-Topper damage parameters more concentrated at the outer edge of the bridge foot; a decrease in the friction coefficient will increase the Smith-Watson-Topper damage parameters in the middle of the contact surface.
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Authors and Affiliations

Xin Zeng
1 2
Xiaoxiao Wang
1 2
Xuecheng Ping
1 2
Renjie Wang
1 2
Tao Hu
3

  1. Tianjin University of Science and Technology, School of Mechanical Engineering, Tianjin 300222, China
  2. Tianjin University of Science and Technology, Tianjin Key Laboratory of Integrated Design and Online Monitoring of Light Industry and Food Engineering Machinery and Equipment, Tianjin 300222, China
  3. Shanghai Xifa Business Consult ing Co., Ltd., Shanghai 200232, China
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Abstract

Adetailed tie model of cracking is proposed. The model is dedicated to both semi-massive RC (reinforcement concrete) members subjected to early-age imposed strains and non-massive members in which imposed strains occur after concrete hardening. As distinct from the currently applied European guidelines, the proposed model enables an analysis of crack width changes. These are a function of progressive imposed strain, material and geometry data, but also depend on the scale of cracking which determines the strain conditions of a member. Consequently, the new model takes account of not only the factors determining the cracking development but also the member relaxation effect that results from cracking. For this reason a new definition of restraint factor is proposed, which takes into account the range of cracking of a structural member, i.e. the number and width of cracks. Parametric analyses were performed of both the changes of the degree of restraint after cracking as well as the changes of crack width depending on the adopted type of aggregate, class of concrete and the coefficient of thermal expansion of concrete. These analyses indicate the potential benefits of the application of the presented model for both a more accurate interpretation of research and economical design of engineering structures.
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Authors and Affiliations

Mariusz Zych
1
ORCID: ORCID

  1. Cracow University of Technology, Faculty of Civil Engineering, St. Warszawska 24, 31-155 Cracow, Poland
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Abstract

One of the worst accidents that can take place in industrial presses is related to the risk of generating cracks in the columns. In order to avoid press columns from being subjected to tensile stress in the loading phase, the columns are sometimes assembled precompressed, so that nominal stress maintains negative values throughout the work cycle. Previous researches have considered cracks propagating under cyclic compressive loads in notched specimens. In these cases, the fatigue cracks are initiated at the notch root due to residual tensile stresses and grew at a progressively decreasing speed before arresting. The subject of the present paper is to give a paradigmatic example of crack initiation and propagation also in a general compressive field.
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Authors and Affiliations

Giorgio Olrni
Alessandro Freddi
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Abstract

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.

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Authors and Affiliations

M. Knauff
B. Grzeszykowski
A. Golubińska
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Abstract

Based on the mould temperature measured by thermocouples during slab continuous casting, a difference of temperature thermograph is developed to detect slab cracks. In order to detect abnormal temperature region caused by longitudinal crack, the suspicious regions are extracted and divided by virtue of computer image processing algorithms, such as threshold segmentation, connected region judgement and boundary tracing. The abnormal regions are then determined and labeled with the eight connected component labeling algorithm. The boundary of abnormal region is also extracted to depict characteristics of longitudinal crack. Based on above researches, longitudinal crack with abnormal temperature region can be detected and is different from other abnormalities. Four samples of temperature drop are picked up to compare with longitudinal crack on the abnormal region formation, length, width, shape, et al. The results show that the abnormal region caused by longitudinal crack has a linear and vertical shape. The height of abnormal region is more than the width obviously. The ratio of height to width is usually larger than that of other temperature drop regions. This method provides a visual and easy way to detect longitudinal crack and other abnormities. Meanwhile it has a positive meaning to the intelligent and visual mould monitoring system of continuous casting.
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Authors and Affiliations

Y. Liu
Y. Gao
X. Wang
Y. Sun
Du F.
F. Wang
J. Wang
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Abstract

Digital holography (DH) which is the technology of acquiring and processing measurement data via a CCD camera is spreading to industrial applications, finds wide employment in engineering problems of testing and investigation. In this paper, a simple digital holographic system, comprising a He-Ne laser source, CCD camera and analyzing software, is used for testing surface flatness and detecting the presence of a propagating crack on the surface plane and the effect of the crack on the neighborhood. Phase variations across the surfaces planes are extracted to represent the surface deviation from a reference plane. The analysis methods differ according to the interference fringes in the recorded holograms. Both fringe tracking and Fourier transform with phase unwrapping methods are used in the interpretation of interferometric fringe patterns.

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Authors and Affiliations

Niveen Maaboud
Mohamed El-Bahrawi
Fedia Abdel-Aziz
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Abstract

The present paper investigates the effects of variable-amplitude loads on fatigue crack growth rates for the 2024-T3 aluminium alloy on the basis of microfractographic analyses and its capacity to reconstruct load-time histories of failed components. For this purpose, there were applied three different variable-amplitude load sequences with single and multiple overloads and underloads. Subsequently, images of fatigue striations on components’ fracture surfaces were examined. The aforementioned loads were employed when simulating fatigue crack behaviour in aeronautical alloys.

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Authors and Affiliations

Zdzisław Bogdanowicz
Dorota Kocańda
Janusz Torzewski
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Abstract

A strip yield model implementation by the present authors is applied to predict fatigue crack growth observed in structural steel specimens under various constant and variable amplitude loading conditions. Attention is paid to the model calibration using the constraint factors in view of the dependence of both the crack closure mechanism and the material stress-strain response on the load history. Prediction capabilities of the model are considered in the context of the incompatibility between the crack growth resistance for constant and variable amplitude loading.

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Authors and Affiliations

Małgorzata Skorupa
Tomasz Machniewicz
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Abstract

The paper presents the results of tests on dynamic stability of Bernoulli-Euler beam with damages. Damages (cracks) were modeled using three rotational springs. An analysis of the influence of crack depth and their position relative to the beam ends on dynamic stability of the beam was carried out. The problem of dynamic stability was solved by applying the mode summation method. Applying an orthogonal condition of eigenfunctions, the dynamic of the system was described with the use of the Mathieu equation. The obtained equation allowed the dynamic stability of the tested system to be analyzed. Stable and unstable solutions were analyzed using the Strutt card.
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Authors and Affiliations

W. Sochacki
1
ORCID: ORCID
S. Garus
1
ORCID: ORCID
J. Garus
1
ORCID: ORCID

  1. Czestochowa University of Technology, Department of Mechanics and Fundamentals of Machinery Design, Faculty of Mechanical Engineering and Computer Science, 73 Dąbrowskiego Str., 42-201 Częstochowa, Poland
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Abstract

Slender systems are mostly studied when Euler’s load or follower load is considered. The use of those types of external loads results in well-known divergence or flutter shape of the characteristic curve. In this study, one takes into account the specific load which allows one to obtain an interesting divergence – pseudo flutter shape of characteristic curves on the external load–vibration frequency plane. The curves can change inclination angle as well as one can observe the change in vibration modes along them. The shape of those curves depends not only on the parameters of the slender system but also on loading heads that induce the specific load. In this study, one considers the slender multimember system in which cracks are present and weaken the host structure. The results of theoretical as well as numerical simulations are focused on the influence of the parameters of the loading heads on vibrations, stability, and loading capacity of the investigated system as well as on the possibility of partial reduction of unwanted crack effect.
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Authors and Affiliations

Krzysztof Sokół
1
ORCID: ORCID
Krzysztof Kuliński
2

  1. Department of Mechanics and Machine Design Foundations, Czestochowa University of Technology, Czestochowa, Poland
  2. Department of Civil Engineering, Czestochowa University of Technology, Czestochowa, Poland
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Abstract

Prediction of propagation time of corrosion is a key element in evaluating the service life of corroded reinforced concrete (RC) structures. Corroded steel products often expand in volume and thus generate tensile stress in the concrete cover. When this tensile stress exceeds the tensile strength of the concrete, cracking occurs. The tensile stresses in concrete due to corrosion are usually perpendicular to the longitudinal axis of the reinforcement. In the reinforced concrete beams, tensile stresses in concrete due to bending is perpendicular to the longitudinal direction of stirrups. In the reinforced concrete slabs, the tensile stresses in concrete due to bending is also perpendicular to the axis of longitudinal reinforcement subjected to bending in the other direction. In such cases, the tensile stresses in concrete due to corrosion of reinforcement has the same direction as the tensile stress caused by bending. When the load-induced stress in the concrete has the same direction as that of the corrosion-induced stress, cracks will likely appear more quickly and vice versa. The main objective of this paper is to build a predictive model of corrosion propagation time taking into account: (1) the effect of stresses due to load; (2) the change of corrosion current density. The model was implemented on Matlab software. The results show the influence of the load, and other parameters on the corrosion propagation stage, when considering the end of this corrosion propagation stage is cracking of concrete cover.
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Authors and Affiliations

Dao Van Dinh
1
ORCID: ORCID
Tran Viet Hung
1
ORCID: ORCID

  1. Structural Engineering Section – University of Transport and Communications Add: No.3 Cau Giay Street, Lang Thuong ward, Dong Da District, Hanoi, Vietnam
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Abstract

The strip yield model from the NASGRO computer software has been applied to predict fatigue crack growth in two different aircraft aluminium alloys under constant amplitude loading and programmed and random variable amplitude load histories. The computation options realized included either of the two different strip yield model implementations available in NASGRO and two types of the input material data description. The model performance has been evaluated based on comparisons between the predicted and observed results. It is concluded that altogether unsatisfactory prediction quality stems from an inadequate constraint factor conception incorporated in the NASGRO models.
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Authors and Affiliations

Małgorzata Skorupa
Tomasz Machniewicz
Andrzej Skorupa
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Abstract

Experimental evaluations on interlaminar and intralaminar fracture of multilayered and sandwich epoxy and polyester fabrics show an interesting behaviour at delamination initiation and crack propagation. Mode I and Mode Il tests were done on layered specimens with same type of ani ficial delamination to investigate the material influence on interlaminar fracture toughness and crack propagation. In sandwich specimens with a rigid foam core, the intralaminar damage failure and propagation are monitored.
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Authors and Affiliations

D.M. Constantinescu
N. Constantin
T. Goss
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Abstract

Rock masses, especially those with different pre-existing cracks, are prone to instability and failure under tensile loading, resulting in different degrees of engineering disasters. Therefore, to better understand the effect of pre-existing cracks with different dip angles on the tensile instability failure behaviour of rocks, the mechanism of crack initiation, propagation and coalescence in precracked sandstone under radial compression loading is investigated through numerical simulations. The temporal and spatial evolution of acoustic emission (AE) events is investigated by the moment tensor (MT), and the fracture mode of micro-cracks is determined. The results show that the pre-existing cracks weaken the specimens. The strength, crack initiation points and macro-failure modes of the specimens differ significantly depending on the dip angle of the pre-existing crack. For different dip angles of the pre-existing cracks, all the micro-cracks at the crack initiation point are tensile cracks, which are dominant during the whole loading process, and mixed cracks are mainly generated near the upper and lower loading ends after the peak stress. Of the total number of events, more than 75% are tensile cracks; approximately 15% are shear mode cracks; and the remainder consist of mixed mode cracks. The study reveals the instability and failure mechanism of pre-cracked rock, which is of great significance to ensure the long-term stability of rock mass engineering.
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Authors and Affiliations

Guozhu Wang
1
ORCID: ORCID
Xulin Luo
2
ORCID: ORCID
Lei Song
3
ORCID: ORCID
Yu Wang
3
ORCID: ORCID
Mouwang Han
3
ORCID: ORCID
Zhaocun Song
3
ORCID: ORCID
Linjun Wu
3
ORCID: ORCID
Zukun Wang
3
ORCID: ORCID

  1. China University of Mining and Technology (CUMT), State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou 221116, China
  2. Zhengzhou University of Industrial Technology, School of Architectural Engineering, Zhengzhou 451150, China
  3. CUMT, Xuzhou 221116, China

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