Investigation of Size Effects on Process Models for Plane Strain Microbending

2006 ◽  
Author(s):  
Richard M. Onyancha ◽  
Brad L. Kinsey
Keyword(s):  
Size Effects ◽  
Strain Distribution ◽  
Past Research ◽  
Peak Force ◽  
Process Models ◽  
Analytical Models ◽  
Linear Strain ◽  
Bending Force ◽  
Bending Process ◽  
Individual Grains

Accurate process models provide vital information in the design of manufacturing processes. To characterize bending operations, analytical models have been developed and shown to predict the peak bending forces fairly accurately for sheets in the macro or mesoscale (i.e. sheets with a large number of grains through the thickness). However, whether these models also accurately predict bending forces for sheets in the microscale (i.e. sheets with approximately ten grains or less through the thickness) has not been evaluated. The present study is aimed at investigating the use of two such models from previous work with microscale bending data. In addition, using these previous models as a foundation, additional bending force models were developed to predict the bending force specifically for microscale bending operations. Data analysis showed that the process models from past research, which provide accurate results for macroscale bending, over predict the peak force required for bending microscale sheets. These process models assume a non-linear strain distribution through the thickness and a curved formed wall. The two models developed in this research provide accurate results for the microscale bending tests, however, they under predict the peak force for the macroscale bending operation. These developed process models assume a linear strain distribution through the thickness and a straight formed wall. The linear strain distribution is more appropriate for the microscale bending process as there are few grains through the thickness and the strain in individual grains varies linearly across the grain. The straight formed wall is more appropriate for the microscale bending process as there is not sufficient distance to warrant a curved formed wall assumption. These differences represent size effects for assumptions in the process models. The material used for these investigations was Brass (CuZn15). The sheets had between 2 and 50 grains through the thickness with grain sizes of between 10 μm and 71 μm.

Comparison of Analytical Models of Force Prediction during Dynamic Bending Stage for 3-Roller Conical Bending Process

2014 ◽  
Vol 1016 ◽  
pp. 150-155
Author(s):  
Mahesh Chudasama ◽  
Harit K. Raval
Keyword(s):  
Shear Stress ◽  
Analytical Model ◽  
Optimum Design ◽  
Experimental Results ◽  
Analytical Models ◽  
Force Prediction ◽  
Bending Force ◽  
Bending Process ◽  
Dynamic Bending ◽  
Bottom Roller

Conical bending process using three rollers with different configurations is a widely used process for manufacturing conical sections and shells in the industries. The process involves static as well dynamic stages. For optimum design of the machine, accurate analytical model of the force prediction is required for static as well dynamic bending stages. In this paper the analytical models considering three different stress conditions have been compared with the experimental results. The observations of the comparison have been reported. It is concluded that for higher bottom roller inclination, the shear stress has to be considered for evaluation of bending force whereas for lower bottom roller inclination it can be neglected.

Subsurface Deformation in Surface Mechanical Attrition Processes

2015 ◽  
Author(s):  
Zhiyu Wang ◽  
Saurabh Basu ◽  
Christopher Saldana
Keyword(s):  
Strain Hardening ◽  
Model Material ◽  
Process Models ◽  
Image Correlation ◽  
Analytical Models ◽  
Subsurface Deformation ◽  
Multi Stage ◽  
Mechanical Attrition ◽  
Dead Metal Zone ◽  
Plane Strain Deformation

A modified expanding cavity model (M-ECM) is developed to describe subsurface deformation for strain-hardening materials loaded in unit deformation configurations occurring in surface mechanical attrition. The predictive results of this model are validated by comparison with unit deformation experiments in a model material, oxygen free high conductivity copper, using a custom designed plane strain deformation setup. Subsurface displacement and strain fields are characterized using in-situ digital image correlation. It is shown that conventional analytical models used to describe plastic response in strain-hardening metals are not able to predict important characteristics of the morphology of the plastic zone, including evolution of the dead metal zone (DMZ), especially at large plastic depths. The M-ECM developed in the present study provides an accurate prediction of the strain distribution obtained in experiment and is of utility as a component in multi-stage process models of the final surface state in surface mechanical attrition.

Effects of Specimen Diameter on Microstructure and Microhardness of Hot Extruded AZ31B Magnesium Alloy

2014 ◽  
Vol 1004-1005 ◽  
pp. 158-162 ◽  
Author(s):  
Xiang Ting Hong ◽  
Fu Chen ◽  
Fei Chen ◽  
Wang Yu ◽  
Bo Rong Sang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Size Effects ◽  
Strain Distribution ◽  
Elevated Temperatures ◽  
Az31b Magnesium Alloy ◽  
Specimen Diameter ◽  
Average Grain Size ◽  
Micro Parts

Microstructures of metal micro parts after microforming at elevated temperatures must be evaluated due to mechanical properties depend on average grain size. In this work, the effects of specimen diameter on the microstructure and microhardness of a hot-extruded AZ31B magnesium alloy were studied. Obvious size effect on microstructure and microhardness of the alloy could be observed. The size effects could be explained by strain distribution and dislocation density differences between the two kinds of specimens.

Study of the Size Effect on Friction Conditions in Microextrusion—Part I: Microextrusion Experiments and Analysis

2006 ◽  
Vol 129 (4) ◽  
pp. 669-676 ◽  
Author(s):  
Neil Krishnan ◽  
Jian Cao ◽  
Kuniaki Dohda
Keyword(s):  
Size Effects ◽  
Circular Cross Section ◽  
High Strength ◽  
Analytical Models ◽  
Homogeneous Material ◽  
Experimental Setup ◽  
Extrusion Force ◽  
Frictional Behavior ◽  
Extrusion Dies ◽  
Metallic Parts

Microforming is a relatively new realm of manufacturing technology that addresses the issues involved in the fabrication of metallic microparts, i.e., metallic parts that have at least two characteristic dimensions in the sub-millimeter range. The recent trend towards miniaturization of products and technology has produced a strong demand for such metallic microparts with extremely small geometric features and high tolerances. Conventional forming technologies, such as extrusion, have encountered new challenges at the microscale due to the influence of “size effects” that tend to be predominant at this length scale. One of the factors that of interest is friction. The two companion papers investigate the frictional behavior and size effects observed during microextrusion in Part I and in a stored-energy Kolsky bar test in Part II. In this first paper, a novel experimental setup consisting of forming assembly and a loading stage has been developed to obtain the force-displacement response for the extrusion of pins made of brass (Cu∕Zn: 70∕30). This experimental setup is used to extrude pins with a circular cross section that have a final extruded diameter ranging from 1.33mm down to 570μm. The experimental results are then compared to finite-element simulations and analytical models to quantify the frictional behavior. It was found that the friction condition was nonuniform and showed a dependence on the dimensions (or size) of the micropin under the assumption of a homogeneous material deformation. Such assumption will be eliminated in Part II where the friction coefficient is more directly measured. Part I also investigates the validity of using high-strength/low-friction die coatings to improve the tribological characteristics observed in micro-extrusion. Three different extrusion dies coated with diamondlike carbon with silicon (DLC-Si), chromium nitride (CrN), and titanium nitride (TiN) were used in the microextrusion experiments. All the coatings worked satisfactorily in reducing the friction and, correspondingly, the extrusion force with the DLC-Si coating producing the best results.

scholarly journals A decade of detailed observations (2008–2018) in steep bedrock permafrost at Matterhorn Hörnligrat (Zermatt, CH)

2019 ◽  
Author(s):  
Samuel Weber ◽  
Jan Beutel ◽  
Reto Da Forno ◽  
Alain Geiger ◽  
Stephan Gruber ◽  
...  
Keyword(s):  
Past Research ◽  
Process Models ◽  
Sensor Technology ◽  
Future Research ◽  
Data Set ◽  
Technological Advances ◽  
Data Record ◽  
History Of ◽  
Diverse Data ◽  
And Control

Abstract. The PermaSense project is an ongoing interdisciplinary effort between geo-science and engineering disciplines started in 2006 with the goals to make observations possible that previously have not been possible. Specifically the aims are to obtain measurements data in unprecedented quantity and quality based on technological advances. This paper describes a unique ten+ year data record obtained from in-situ measurements in steep bedrock permafrost in an Alpine environment on the Matterhorn Hörnligrat, Zermatt Switzerland at 3500 m a.s.l. Through the utilization of state-of-the-art wireless sensor technology it was possible to obtain more data of higher quality, make this data available in near real-time and tightly monitor and control the running experiments. This data set (DOI: https://doi.org/10.1594/PANGAEA.897640, Weber et al., 2019a) constitutes the longest, densest and most diverse data record in the history of mountain permafrost research worldwide with 17 different sensor types used at 29 distinct sensor locations consisting of over 114.5 million data points captured over a period of ten+ years. By documenting and sharing this data in this form we contribute to making our past research reproducible and facilitate future research based on this data e.g. in the area of analysis methodology, comparative studies, assessment of change in the environment, natural hazard warning and the development of process models.

The improvement of stress correction in post-necking tension of cylindrical specimen

2019 ◽  
Vol 54 (3) ◽  
pp. 209-222 ◽  
Author(s):  
Junfu Chen ◽  
Zhiping Guan ◽  
Pinkui Ma ◽  
Zhigang Li ◽  
Xiangrui Meng
Keyword(s):  
Cross Section ◽  
Strain Distribution ◽  
Prediction Accuracy ◽  
Inverse Method ◽  
Cylindrical Specimen ◽  
Analytical Models ◽  
Large Strains ◽  
Stress And Strain ◽  
Simulation Results ◽  
Prediction Capability

In post-necking tension of cylindrical specimen, the stress corrections based on the current analytical models have relatively significant errors at large strains. In this study, the prediction capability of these models involving Bridgman model, Siebel model and Chen model is evaluated by performing a series of finite element simulations of uniaxial tension of cylindrical specimen with different hardening exponents varied from 0.05 to 0.3. Numerical analysis of stress and strain distributions on the necking cross section indicates that the considerable errors of the corrected stresses corresponding to large strains might be mainly attributed to the assumption of uniform strain distribution on the necking cross section in these analytical models. The modification strategies of these models are presented in order to improve their prediction accuracy of post-necking stresses, taking geometrical configuration of neck and material properties into consideration. Accordingly, the modification formulas are proposed based on simulation results, involving the radius of cross section of neck and the hardening exponent. Finally, these formulas are used to correct the stresses in the post-necking tension of Q345 cylindrical specimen, which are compared with the stresses identified through inverse method. The results indicate that the modified models significantly improve the prediction accuracy of post-necking stresses at large strains.

A Transient Thermoelastoplastic Solution for a Hollow Sphere of Temperature Dependent Properties

1995 ◽  
Author(s):  
Shahriar Jahanian
Keyword(s):  
Hollow Sphere ◽  
Strain Distribution ◽  
Residual Stress Distribution ◽  
Stress And Strain ◽  
Linear Strain ◽  
Temperature Dependent ◽  
History Of ◽  
Temperature Dependent Properties ◽  
Stress And Strain Distribution ◽  
Incremental Theory Of Plasticity

Abstract In this paper an analysis based on incremental theory of plasticity is formulated to predict the thermoelastoplastic stresses in a hollow sphere. The properties of the material are assumed to be temperature dependent, and the material was characterized by linear strain hardening. Mendeson’s method of successive elastic solution is presented for the analysis. The analysis shows that the stresses are not monotonic function of radius or temperature, they strongly depend on history of temperature distribution. In this analysis the problem is treated in a uncoupled, and quasi-static sense. The plastic stress and strain distribution on loading and the residual stress distribution on unloading is presented. The results are compared with the results of other investigators who used a different theory and a reasonable agreement is observed.

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