scholarly journals Understanding the edge crack phenomenon in ceramic laminates

2015 ◽  
Author(s):  
O. Ševeek, ◽  
M. Kotoul ◽  
D. Leguillon ◽  
E. Martin ◽  
R. Bermejo
Keyword(s):  
Residual Stresses ◽  
Edge Crack ◽  
Energy Criterion ◽  
Element Model ◽  
Ceramic Materials ◽  
Brittle Behavior ◽  
Compressive Stresses ◽  
Out Of Plane ◽  
Edge Cracks ◽  
Edge Cracking

Layered ceramic materials (also referred to as “ceramic laminates”) are becoming one of the most promising areas of materials technology aiming to improve the brittle behavior of bulk ceramics. The utilization of tailored compressive residual stresses acting as physical barriers to crack propagation has already succeeded in many ceramic systems. Relatively thick compressive layers located below the surface have proven very effective to enhance the fracture resistance and provide a minimum strength for the material. However, internal compressive stresses result in out-of plane stresses at the free surfaces, what can cause cracking of the compressive layer, forming the so-called edge cracks. Experimental observations have shown that edge cracking may be associated with the magnitude of the compressive stresses and with the thickness of the compressive layer. However, an understanding of the parameters related to the onset and extension of such edge cracks in the compressive layers is still lacking. In this work, a 2D parametric finite element model has been developed to predict the onset and propagation of an edge crack in ceramic laminates using a coupled stress-energy criterion. This approach states that a crack is originated when both stress and energy criteria are fulfilled simultaneously. Several designs with different residual stresses and a given thickness in the compressive layers have been computed. The results predict the existence of a lower bound, below no edge crack will be observed, and an upper bound, beyond which the onset of an edge crack would lead to the complete fracture of the layer.

Fracture of Layered Ceramics

2009 ◽  
Vol 409 ◽  
pp. 94-106 ◽  
Author(s):  
Raúl Bermejo ◽  
Luca Ceseracciu ◽  
Luis Llanes ◽  
Marc Anglada
Keyword(s):  
Residual Stresses ◽  
Thermal Strain ◽  
Ceramic Materials ◽  
Layered Structures ◽  
Internal Layers ◽  
Multilayered Structures ◽  
Compressive Stresses ◽  
Layered Ceramics ◽  
Different Response ◽  
Experimental Findings

Layered ceramics are foreseen as possible substitutes for monolithic ceramics due to their attractive mechanical properties in terms of strength reliability and toughness. The different loading conditions to which ceramic materials may be subjected in service encourage the design of tailored layered structures as function of their application. The use of residual stresses generated during cooling due to the different thermal strain of adjacent layers has been the keystone for the improvement of the fracture response of many layered ceramic systems, e.g. alumina-zirconia, alumina-mullite, silicon nitride-titanium nitride, etc. In this work, the fracture features of layered ceramics are addressed analysing two multilayered structures, based on the alumina-zirconia system, designed with tailored compressive residual stresses either in the external or internal layers. Contact strength and indentation strength tests have been performed to investigate the response of both designs to crack propagation. The experimental findings show a different response in terms of strength and crack growth resistance of both designs. While layered structures with compressive stresses at the surface provide a better response against contact damage compared to monoliths, a flaw tolerant design in terms of strength and an improved toughness through energy release mechanisms is achieved with internal compressive stresses. The use of layered architectures for automotive or biomedical applications as substitutes for alumina-based ceramics should be regarded in the near future, where reliable ceramic designs are needed.

scholarly journals The Computation and Measurement of Residual Stresses in Laser Deposited Layers

2003 ◽  
Vol 125 (3) ◽  
pp. 302-308 ◽  
Author(s):  
S. Finnie ◽  
W. Cheng ◽  
I. Finnie ◽  
J. M. Drezet ◽  
M. Gremaud
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Residual Stresses ◽  
Metal Forming ◽  
Steel Substrate ◽  
Plane Deformation ◽  
Compressive Stresses ◽  
Out Of Plane ◽  
Simulation And Experiment ◽  
Melted Material

Laser metal forming is an attractive process for rapid prototyping or the rebuilding of worn parts. However, large tensile stress may arise in layers deposited by laser melting of powder. A potential solution is to preheat the substrate before and during deposition of layers to introduce sufficient contraction during cooling in the substrate to modify the residual stress distribution in the deposited layers. To demonstrate the value of this approach, specimens were prepared by depositing stellite F on a stainless steel substrate with and without preheating. Residual stresses were computed by numerical simulation and measured using the crack compliance method. For non-preheated specimens simulation and experiment agreed well and showed that extremely high residual tensile stresses were present in the laser melted material. By contrast, pre-heated specimens show high compressive stresses in the clad material. However, in this case the numerical simulation and experimental measurement showed very different stress distribution. This is attributed to out of plane deformation due to the high compressive stresses which are not permitted in the numerical simulation. A “strength of materials” analysis of the effect of out of plane deformation was used to correct the simulation, Agreement with experimental results was then satisfactory.

scholarly journals Thermo-Mechanical Modeling of Wire-Fed Electron Beam Additive Manufacturing

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 911
Author(s):  
Fatih Sikan ◽  
Priti Wanjara ◽  
Javad Gholipour ◽  
Amit Kumar ◽  
Mathieu Brochu
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Residual Stresses ◽  
Single Layer ◽  
Grain Morphology ◽  
Element Model ◽  
Primary Objective ◽  
Average Error ◽  
Thin Wall ◽  
Compressive Stresses

The primary objective of this research was to develop a finite element model specifically designed for electron beam additive manufacturing (EBAM) of Ti-6Al-4V to understand metallurgical and mechanical aspects of the process. Multiple single-layer and 10-layer build Ti-6Al-4V samples were fabricated to validate the simulation results and ensure the reliability of the developed model. Thin wall plates of 3 mm thickness were used as substrates. Thermocouple measurements were recorded to validate the simulated thermal cycles. Predicted and measured temperatures, residual stresses, and distortion profiles showed that the model is quite reliable. The thermal predictions of the model, when validated experimentally, gave a low average error of 3.7%. The model proved to be extremely successful for predicting the cooling rates, grain morphology, and the microstructure. The maximum deviations observed in the mechanical predictions of the model were as low as 100 MPa in residual stresses and 0.05 mm in distortion. Tensile residual stresses were observed in the deposit and the heat-affected zone, while compressive stresses were observed in the core of the substrate. The highest tensile residual stress observed in the deposit was approximately 1.0 σys (yield strength). The highest distortion on the substrate was approximately 0.2 mm.

Numerical Modeling of Steel Surface Hardening in the Process of High Energy Heating by High Frequency Currents

2014 ◽  
Vol 698 ◽  
pp. 288-293 ◽  
Author(s):  
Vadim Yu. Skeeba ◽  
Vladimir Ivancivsky ◽  
Valeriy Pushnin
Keyword(s):  
Residual Stresses ◽  
High Frequency ◽  
Process Variations ◽  
Carbon Diffusion ◽  
Element Model ◽  
Hardened Layer ◽  
High Energy ◽  
Plastic Behavior ◽  
Heating Rates ◽  
Compressive Stresses

Surface layer modification methods using concentrated energy sources to ensure high heating rates of approximately 104 – 105 °C/s are becoming increasingly common in an attempt to improve operational performance of machine components. As a result, it is quite difficult to determine heat cycle parameters by means of experiments to predict the required intensity and distribution behavior of residual stresses and strains. The paper addresses the issue of numerical simulation of the stress-strain behavior during high energy heating by high frequency currents (HFC HEH). A finite element model has been generated using the ANSYS and SYSWELD software based on numerical computations of differential equations for transient heat conduction (Fourier equation), carbon diffusion (Fick's second law), and the elastic-plastic behavior of the material. The simulation data was verified by full-scale experiments using optical and scanning microscopy and mechanical and X-ray methods to determine residual stresses. It has been established that the level of residual compressive stresses on the component surface can be from-500 to-1000 MPa within the range of HFC HEH process variations under review. It is proven in theory and confirmed by experiments that the transition layer thickness must amount to 25 – 33 % of the hardened layer depth for the tensile stress peak to shift to deeper material layers while compressive stresses on the surface decrease by 6 – 10 %, in order to prevent hardening cracks.

Residual Stresses in Laminar Functionally Graded Ceramic Materials

2007 ◽  
Vol 333 ◽  
pp. 259-262
Author(s):  
Pavol Hvizdoš ◽  
Kristoffer Norberg
Keyword(s):  
Residual Stresses ◽  
Analytical Model ◽  
Plate Theory ◽  
Element Model ◽  
Ceramic Materials ◽  
Functionally Graded ◽  
Simple Analytical Model ◽  
Free Surfaces ◽  
Material Parameters ◽  
Graded Material

A simple analytical model of residual stresses far from edges in symmetrical planar functionally graded material (FGM) is presented. The model is based on elastic plate theory and neglects the influence of edges and free surfaces. The results are compared to analytical model of laminar ceramics and to finite element model of FGM. The influence of various geometrical and material parameters on the internal stress state is discussed.

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

scholarly journals Thermal Effects on Surface and Subsurface Modifications in Laser-Combined Deep Rolling

2021 ◽  
Vol 5 (2) ◽  
pp. 55
Author(s):  
Robert Zmich ◽  
Daniel Meyer
Keyword(s):  
Surface Layer ◽  
Residual Stresses ◽  
Thermal Loads ◽  
Deep Rolling ◽  
Mechanical Loads ◽  
Thermomechanical Process ◽  
Compressive Stresses ◽  
New Process ◽  
Negative Effect ◽  
Compressive Residual Stresses

Knowledge of the relationships between thermomechanical process loads and the resulting modifications in the surface layer enables targeted adjustments of the required surface integrity independent of the manufacturing process. In various processes with thermomechanical impact, thermal and mechanical loads act simultaneously and affect each other. Thus, the effects on the modifications are interdependent. To gain a better understanding of the interactions of the two loads, it is necessary to vary thermal and mechanical loads independently. A new process of laser-combined deep rolling can fulfil exactly this requirement. The presented findings demonstrate that thermal loads can support the generation of residual compressive stresses to a certain extent. If the thermal loads are increased further, this has a negative effect on the surface layer and the residual stresses are shifted in the direction of tension. The results show the optimum range of thermal loads to further increase the compressive residual stresses in the surface layer and allow to gain a better understanding of the interactions between thermal and mechanical loads.

Estimation of Residual Stress in Spiral Welded Pipe: Regression and Numerical Model

2012 ◽  
Author(s):  
Abul Fazal M. Arif ◽  
Ahmad S. Al-Omari ◽  
Anwar K. Sheikh ◽  
Yagoub Al-Nassar ◽  
M. Anis
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Critical Role ◽  
Large Diameter ◽  
Element Model ◽  
Regression Equation ◽  
Field Analysis ◽  
Welding Parameters ◽  
Splitting Test ◽  
Welded Pipe

Double submerged spiral-welded pipe (SWP) is used extensively throughout the world for large-diameter pipelines. Fabrication-induced residual stresses in spiral welded pipe have received increasing attention in gas, oil and petrochemical industry. Several studies reported in the literature verify the critical role of residual stresses in the failure of these pipes. Therefore, it is important that such stresses are accounted for in safety assessment procedures such as the British R6 and BS7910. This can be done only when detailed information on the residual stress distribution in the component is known. In industry, residual stresses in spiral welded pipe are measured experimentally by means of destructive techniques known as Ring Splitting Test. In this study, statistical analysis and linear-regression modeling were used to study the effect of several structural, material and welding parameters on ring splitting test opening for spiral welded pipes. The experimental results were employed to develop an appropriate regression equation, and to predict the residual stress on the spiral welded pipes. It was found that the developed regression equation explains 36.48% of the variability in the ring opening. In the second part, a 3-D finite element model is presented to perform coupled-field analysis of the welding of spiral pipe. Using this model, temperature as well as stress fields in the region of the weld edges is predicted.

scholarly journals Effect of Al2O3 Sandblasting Particle Size on the Surface Topography and Residual Compressive Stresses of Three Different Dental Zirconia Grades

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 610
Author(s):  
Hee-Kyung Kim ◽  
Byungmin Ahn
Keyword(s):  
Particle Size ◽  
Residual Stresses ◽  
Surface Topography ◽  
Tetragonal Zirconia ◽  
Peak Shift ◽  
Confocal Laser ◽  
Compressive Stresses ◽  
Surface Topographies ◽  
Altered Surface ◽  
Tetragonal Zirconia Polycrystal

This study investigated the effect of sandblasting particle size on the surface topography and compressive stresses of conventional zirconia (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) and two highly translucent zirconia (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ). Plate-shaped zirconia specimens (14.0 × 14.0 × 1.0 mm3, n = 60 for each grade) were sandblasted using different Al2O3 sizes (25, 50, 90, 110, and 125 μm) under 0.2 MPa for 10 s/cm2 at a 10 mm distance and a 90° angle. The surface topography was characterized using a 3-D confocal laser microscopy and inspected with a scanning electron microscope. To assess residual stresses, the tetragonal peak shift at 147 cm−1 was traced using micro-Raman spectroscopy. Al2O3 sandblasting altered surface topographies (p < 0.05), although highly translucent zirconia showed more pronounced changes compared to conventional zirconia. 5Y-PSZ abraded with 110 μm sand showed the highest Sa value (0.76 ± 0.12 μm). Larger particle induced more compressive stresses for 3Y-TZP (p < 0.05), while only 25 μm sand induced residual stresses for 5Y-PSZ. Al2O3 sandblasting with 110 μm sand for 3Y-TZP, 90 μm sand for 4Y-PSZ, and 25 μm sand for 5Y-PSZ were considered as the recommended blasting conditions.

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