Application of a Criterion for Cold Cracking to Casting High Strength Aluminium Alloys

2010 ◽  
Vol 654-656 ◽  
pp. 1432-1435 ◽  
Author(s):  
Mehdi Lalpoor ◽  
Dmitry G. Eskin ◽  
Hallvard Gustav Fjær ◽  
Andreas Ten Cate ◽  
Nick Ontijt ◽  
...  
Keyword(s):  
Thermal Stresses ◽  
Stress Component ◽  
Research Work ◽  
High Strength ◽  
Crack Size ◽  
Cold Cracking ◽  
Critical Crack ◽  
Dc Casting ◽  
Constitutive Parameters ◽  
Cast Condition

Direct chill (DC) casting of high strength 7xxx series aluminum alloys is difficult mainly due to solidification cracking (hot cracks) and solid state cracking (cold cracks). Poor thermal properties along with extreme brittleness in the as-cast condition make DC-casting of such alloys a challenging process. Therefore, a criterion that can predict the catastrophic failure and cold cracking of the ingots would be highly beneficial to the aluminum industry. The already established criteria are dealing with the maximum principal stress component in the ingot and the plane strain fracture toughness (KIc) of the alloy under discussion. In this research work such a criterion was applied to a typical 7xxx series alloy which is highly prone to cold cracking. The mechanical properties, constitutive parameters, as well as the KIc values of the alloy were determined experimentally in the genuine as-cast condition and used as input data for the finite element package ALSIM5. Thermomechanical simulations were run for billets of various diameters and the state of residual thermal stresses was determined. Following the contour maps of the critical crack size gained from the model, the casting conditions were optimized to produce a crack-free billet.

Numerical Simulation of Residual Thermal Stresses in AA7050 Alloy during DC-Casting Using ALSIM5

2010 ◽  
Vol 89-91 ◽  
pp. 319-324 ◽  
Author(s):  
Mehdi Lalpoor ◽  
Dmitry G. Eskin ◽  
Laurens Katgerman
Keyword(s):  
Thermal Stresses ◽  
Numerical Models ◽  
High Strength ◽  
Cold Cracking ◽  
Catastrophic Failure ◽  
Compressive Stresses ◽  
Micro Cracks ◽  
Dc Casting ◽  
High Strength Aluminum Alloys ◽  
Constitutive Parameters

Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of micro-cracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine as-cast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking.

Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel

2012 ◽  
Vol 504-506 ◽  
pp. 901-906 ◽  
Author(s):  
Antti Määttä ◽  
Antti Järvenpää ◽  
Matias Jaskari ◽  
Kari Mäntyjärvi ◽  
Jussi A. Karjalainen
Keyword(s):  
Surface Defects ◽  
High Strength Steels ◽  
Steel Structures ◽  
High Strength ◽  
Crack Size ◽  
Critical Crack ◽  
Bending Radius ◽  
Ultra High Strength Steels ◽  
Materials Used ◽  
Critical Crack Size

The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.

Numerical and Experimental Analysis of Linear Elastic Fracture Mechanics

2004 ◽  
Author(s):  
Muhammad Afzaal Malik ◽  
Batool H. Sayyed ◽  
Shahab Khushnood
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Research Work ◽  
Crack Size ◽  
Linear Elastic Fracture Mechanics ◽  
Point Of View ◽  
Experimental Investigations ◽  
Critical Crack ◽  
Linear Elastic ◽  
Elastic Fracture

Crack propagation in materials can lead to catastrophic failures. The understanding of crack propagation in materials is of crucial importance in many industries, including nuclear, chemical and aeronautical applications. From an engineering point of view, fracture mechanics is used as a basis for predicting critical crack size, strength of a structure as a function of crack size, inspection requirements pertaining to size of an admissible crack and the period of time between inspections. It is usually required to determine the distribution of stresses and strains in a body that is subjected to external loads or displacements. The closed form solutions for crack propagation are rarely available. A numerical simulation of such problems is therefore required. This research work uses Finite Element Method (FEM) for Linear Elastic Fracture Mechanics (LEFM) to predict Stress Intensity Factor (SIF) for different crack geometries. The validation of the results based on modeling and simulation is carried out through comparison with our experimental investigations for crack propagation using photo-elastic methods.

High Strain Rate Fracture Properties of High Strength Steels and Their Application

2011 ◽  
Author(s):  
Alan M. Clayton ◽  
John Dabinett
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Cast Steel ◽  
High Strength Steels ◽  
High Strength ◽  
Crack Size ◽  
Strength Properties ◽  
Strain Rates ◽  
Critical Crack ◽  
Welded Steel

The evaluation of fracture of ferritic steels using the methods in ASME Code Case 2564 for impulsively loaded vessels requires the static reference temperature T0 and the upper shelf toughness, and these are used together with the Master Curve to define the transition temperature curve. The effect of high rates of strain on the ductile-brittle transition is determined in the code case using a correlation due to Wallin. Two steels used for impulsively loaded vessels, welded steel similar to HY80 plate and a cast steel similar to HY100 have been evaluated to obtain their static fracture and strength properties. Additional instrumented pre-cracked Charpy testing using a draft ISO standard has determined the shift in T0 with high strain rates and the results have been compared to the Wallin correlation. The strain rate correlation is used to evaluate the fracture response of vessels made of these steels when subjected to internal blast. By using the instantaneous strain rates of the vessel wall vibration considerable gains in critical crack size can be obtained compared to using the highest rate throughout the whole of the transient.

scholarly journals Thermal Stresses in Chemically Hardening Elastic Media With Application to the Molding Process

1974 ◽  
Vol 41 (3) ◽  
pp. 647-651 ◽  
Author(s):  
Myron Levitsky ◽  
Bernard W. Shaffer
Keyword(s):  
Residual Stress ◽  
Chemical Reaction ◽  
Thermal Stresses ◽  
Stress Component ◽  
Elastic Solid ◽  
Molding Process ◽  
Hardening Process ◽  
Exothermic Chemical Reaction ◽  
Component Parallel

A method has been formulated for the determination of thermal stresses in materials which harden in the presence of an exothermic chemical reaction. Hardening is described by the transformation of the material from an inviscid liquid-like state into an elastic solid, where intermediate states consist of a mixture of the two, in a ratio which is determined by the degree of chemical reaction. The method is illustrated in terms of an infinite slab cast between two rigid mold surfaces. It is found that the stress component normal to the slab surfaces vanishes in the residual state, so that removal of the slab from the mold leaves the remaining residual stress unchanged. On the other hand, the residual stress component parallel to the slab surfaces does not vanish. Its distribution is described as a function of the parameters of the hardening process.

Effect of Rotational Stiffness Evolution at Crack Part on Critical Crack Size in SFR

2012 ◽  
Author(s):  
Takashi Wakai ◽  
Hideo Machida ◽  
Shinji Yoshida
Keyword(s):  
Evaluation Method ◽  
Large Diameter ◽  
Crack Size ◽  
Evolution Model ◽  
Piping System ◽  
Rotational Stiffness ◽  
Critical Crack ◽  
Rotational Spring Model ◽  
Size Evaluation ◽  
Critical Crack Size

This paper describes the efficiency of the deployment of rotational stiffness evolution model in the critical crack size evaluation for Leak Before Break (LBB) assessment of Sodium cooled Fast Reactor (SFR) pipes. The authors have developed a critical crack size evaluation method for the thin-walled large diameter pipe made of modified 9Cr-1Mo steel. In this method, since the SFR pipe is mainly subjected to displacement controlled load caused by thermal expansion, the stress at the crack part is estimated taking stiffness evolution due to crack into account. The stiffness evolution is evaluated by using the rotational spring model. In this study, critical crack sizes for several pipes having some elbows were evaluated and discuss about the effect of the deployment of the stiffness evolution model at the crack part on critical crack size. If there were few elbows in pipe, thermal stress at the crack part was remarkably reduced by considering the stiffness evolution. In contrast, in the case where the compliance of the piping system was small, the critical crack size could be estimated under displacement controlled condition. As a result, the critical crack size increases by employing the model and LBB range may be expected to be enlarged.

Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

2009 ◽  
Author(s):  
Irene Garcia Garcia ◽  
Radoslav Stefanovic
Keyword(s):  
Heat Treatment ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Operational Experience ◽  
Element Analysis ◽  
Critical Crack ◽  
Circumferential Welds ◽  
Fea Model ◽  
Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

scholarly journals Optimization of Drilling Process Parameters Via Taguchi, TOPSIS and RSA Techniques

2017 ◽  
Vol 62 (3) ◽  
pp. 1803-1812 ◽  
Author(s):  
K. Shunmugesh ◽  
K. Panneerselvam
Keyword(s):  
Process Parameters ◽  
Feed Rate ◽  
Research Work ◽  
Cutting Speed ◽  
High Strength ◽  
Drilling Process ◽  
Drill Bit ◽  
Influence Of Process Parameters ◽  
Light Trucks ◽  
Cfrp Composite

AbstractCarbon Fiber Reinforced Polymer (CFRP) is the most preferred composite material due to its high strength, high modulus, corrosion resistance and rigidity and which has wide applications in aerospace engineering, automobile sector, sports instrumentation, light trucks, airframes. This paper is an attempt to carry out drilling experiments as per Taguchi’s L27(313) orthogonal array on CFRP under dry condition with three different drill bit type (HSS, TiAlN and TiN). In this research work Response Surface Analysis (RSA) is used to correlate the effect of process parameters (cutting speed and feed rate) on thrust force, torque, vibration and surface roughness. This paper also focuses on determining the optimum combination of input process parameter and the drill bit type that produces quality holes in CFRP composite laminate using Multi-objective Taguchi technique and TOPSIS. The percentage of contribution, influence of process parameters and adequacy of the second order regression model is carried out by analysis of variance (ANOVA). The results of experimental investigation demonstrates that feed rate is the pre-dominate factor which affects the response variables.

Applying Gurson Type of Damage Models to Low Constraint Tests of High Strength Steels and Welds

2006 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang
Keyword(s):  
Damage Mechanics ◽  
Ductile Failure ◽  
High Strength Steels ◽  
High Strength ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Gtn Model ◽  
Strain Capacity ◽  
Low Constraint

Pipelines experiencing displacement-controlled loading need to have adequate strain capacity. Large tensile strain capacity can only be achieved when the failure processes are ductile. In ductile failure analyses, the strain capacity may be determined by two approaches. The first approach uses the conventional fracture mechanics criteria, such as the attainment of the critical crack tip opening displacement, to assess the onset of the crack propagation. The other approach uses damage mechanics models in which the onset and propagation of cracks are controlled by the nucleation, growth, and coalescence of voids in the material. The damage mechanics models can provide some insights of the ductile failure processes as they have more physical mechanisms built in the constitutive model. In this paper, the Gurson-Tvergaard-Needleman (GTN) model is applied to two types of low-constraint tests: curved wide plates and back-bend specimens. The wide plate test is considered more representatives of full-scale pipes than the conventional laboratory-sized specimens, but requires large-capacity machines. The back-bend test is a newly developed low-constraint laboratory-sized test specimen. A relatively simple approach to determine the damage parameters of the GTN model is discussed and the transferability of damage parameters between those two test types is also analyzed.

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