Explore: Distortion

A method for quantifying distortions arising in engine blocks of aluminum with liners of gray iron has been developed based on virtual finite element-based simulation tools. The key processing steps comprise the convection cooling step, associated with shrinkage and residual stress build-up, and the machining step. The engine block has been modeled using the finite element method and machining has been simulated using the element-removal technique. The mechanical behavior of aluminum has been characterized by tensile tests at different temperatures and strain rates. The results were used for calibration of a material model capturing the viscoplastic behavior at higher temperatures. Finally, to illustrate the key process steps, results from a complete process analysis are reported comprising the initial stress build-up during cooling and the initial out-of-roundness and out-of-roundness of the liners after various machining operations.

A brief survey of various empirical strength theories that have been proposed for anisotropic materials is given. Working equations for the various strength criteria are discussed and the best criteria are selected. Weaknesses of some of the criteria are also indicated.

This article discusses the subtleties of spray quenching in induction surface hardening (case hardening) and selective hardening applications utilizing scanning and single-shot heating modes. Computer modeling provides the ability to predict how different factors may impact the transient and final heat-treating conditions of the workpiece and what must be accomplished in the design of the induction heating system to improve the effectiveness of the process and guarantee the desired results. One of the major features of computation of induction hardening processes deals with the specifics of modeling, i.e., both heating and quenching stages that can often be overlapped in time. Water or water-based polymers are the most popular types of quenchants used with induction hardening. Results of computer modeling of different induction hardening applications, using Inductoheat's proprietary finite element codes, are presented here as well.

Thermal shock damage may be a precursor to the melting and disordering of metallic reflector surfaces. A number of investigators have reported in these proceedings the phenomena of slip fracture on the surfaces of both polished and diamond turned optics. In this paper, a model is presented using elastic-plastic technique coupled with the transient thermal response of an optical surface.

Quenching is a complex thermo-mechano-metallurgical problem. Unexplored or without an optimized cooling strategy, a quenching process can end up with high residual stresses and distortion. This paper presents the mathematical formulation of the physics behind the quenching process, the numerical technique and optimization of the cooling strategies for the selected geometries. The finite element method (FEM) is used to solve the coupled partial differential equations in the framework of an isothermal-staggered approach. The solid-solid phase transformations are modeled using a linear iso-kinetic law with Schiel's additivity rule and Koistinen-Marburger (KM) law. The thermoplastic material model is formulated on the basis of J2-plasticity theory with a temperature and phase fraction-dependent yield limit together with the appropriate mixture rule. The coupling effects such as phase transformation enthalpy, transformation-induced plasticity and dissipation are considered. The local heat transfer coefficient (HTC) during the quenching process plays a crucial role for the evolution of the distortion and residual stresses. It is demonstrated that with an enhanced quenching at the mass lumped regions, the distortion can be reduced. It is always possible to find an HTC profile which eliminates the distortion completely on the expense of an increased residual stress state. Therefore, an optimum quenching strategy has to be found to reduce the distortion and the residual stresses simultaneously. It is shown that with an enhanced quenching at the mass lumped regions and with a reduced quenching at the edges and corners, stresses and distortion can be minimized simultaneously. Examples are given for different kinds of metals and geometries such as long profiles (L and T) and disk with a hole.

An early warning sign of Age-Related Macular Degeneration (AMD) is the presence of drusen, tiny yellow deposits that accumulate between the Retinal Pigment Epithelium (RPM) and Bruch's membrane (BM). Large scaled drusens in more advanced staged AMD can distort the overlying inner retinal layers and lead to incorrect IPL/INL boundary segmentation. This distortion can lead to incorrect segmentation of the inner retinal layers of the eye. This inaccurate segmentation could potentially result in erroneous conclusions when macular Optical Coherence Tomography (OCT) imaging detects glaucoma or its progression as the ocular disease mainly manifests itself within the inner retinal layers. This study uses a CNN-based algorithm to automate drusen segmentation in OCT scans. Drusens features were extracted from the algorithms' results and used to correlate the extent of drusens features and inaccurate segmentation of inner retinal layers in patients with concurrent glaucoma and AMD. Normalized drusen height was the strongest predictor for segmentation error among the features derived from drusens in AMD eyes. We found that automated segmentation has a moderate chance of failure if the drusen height is 145-185Îơm and is likely to fail with drusen heights above 185Îơm. Our findings can enlighten OCT device manufacturers and the clinical and research community about the possibility of missing a glaucoma diagnosis in an already established AMD patient.

FLUENT was used to simulate the quenchant flow through a quench rack of automotive pinions. Utilizing a typical heat treat rack arrangement, two parts in an actual rack of heat treated pinions were then evaluated by finite element simulations using the finite element software, DANTE®, using the CFD results as boundary conditions for the finite element analysis. Part shape change, internal stress, and phase transformation histories were calculated for this carburized pinion gear made of AISI 8620.

Results of an experimental study of the effect of polyisobutilene additives to mineral oils I-20A, I-12A, and I-8A on their cooling characteristics are provided. It is shown that a small amount of the polyisobutilene oligomer in mineral oil I-20A (3 %) can completely eliminate a film-boiling process during the quenching of steel parts and make a significantly shorter period of film-boiling during quenching in oils I-12A and I-8A. In this case, a surface of steel parts is cooled intensively and constantly, the part distortion is minimal, and hardness is greater and more consistent. The results of the study were applied to bearing products produced by the Svenska Kullagerfabriken AB (SKF) bearing plant (Lutsk, Ukraine).

Polyalkylene glycol quenchants (also commonly called "glycol" quenchants throughout the industry) were introduced into the aluminum heat treating industry in the mid 1960s and immediately became the most important tool for reducing quenching distortion in sheet metal alloys. Later, the feasibility and benefit of glycol quenching thicker products, such as castings and forgings (which were normally quenched in hot or boiling water), was proven. Specifications were changed to permit glycol quenching of forgings and castings. However, because of a lack of understanding of the technology, the original benefits achieved in sheet metal distortion control and optimum distortion and residual stress control of thicker products has diminished. Currently, there is a significant lack of understanding regarding glycol quenching and, as a result, the full benefit of this technology is not currently being utilized. Distortion of sheet metal products and precision forgings has increased, resulting in increased check and straightening costs and higher residual stresses being imparted to parts. The realization of the benefits of glycols being able to reduce residual stress and ultimately machining costs is waning due to the reluctance of many engineers to recognize and understand the benefits of expanding the limits of the technology to achieve results not heretofore achievable. It is the purpose of this paper to review the basic concepts regarding glycol quenching of high strength aluminum alloys and to present recommendations for optimum control of distortion and residual stresses using the products. Specific illustrations showing that the proper use of glycol quenchants can provide the producer significant savings by (1) reducing quenching distortion and (2) minimizing residual stresses (which significantly improve machining practices and reduce the generation of scrap) are provided.

Some degree of distortion is found in all bite marks. That distortion can be caused by photographic methods of recording the mark, by the dynamics of the bite, or by artifaction. All types of distortion complicate the process of matching marks to dentition, thus making it important to understand the distortion and, if possible, correct or allow for it. A method of analyzing photographically distorted bite patterns is presented, future research directions are suggested, and evidence-gathering standards are stressed.