A void evolution model accounting for stress triaxiality, Lode parameter and effective strain for hot metal forming

2020 ◽  
Vol 168 ◽  
pp. 105309 ◽  
Author(s):  
Xinbao Wang ◽  
Xianghuai Dong
Keyword(s):  
Metal Forming ◽  
Effective Strain ◽  
Stress Triaxiality ◽  
Evolution Model ◽  
Hot Metal ◽  
Lode Parameter ◽  
Void Evolution

scholarly journals Hot and cold flashless forging in vertical split dies of a stepped shaft

2021 ◽  
Author(s):  
Tomasz Bulzak ◽  
Janusz Tomczak ◽  
Zbigniew Pater
Keyword(s):  
Metal Forming ◽  
Effective Strain ◽  
Cold Forging ◽  
Geometrical Parameters ◽  
Hot Metal ◽  
Numerical Tests ◽  
Forming Technology ◽  
Stepped Shaft ◽  
One Step ◽  
Manufacturing Time

Abstract Flashless forging is classified as a precise metal forming technology. The main advantages of this technology are the reduction of the flash allowance and the shortening of the manufacturing time by eliminating the flash trimming operation. The article presents the process of one-step forging of a stepped shaft made of aluminum with the use of split dies. The process was carried out in cold and hot metal forming conditions. The forging process was analyzed numerically using the Simufact.Forming 15.0 software. The geometrical parameters of the obtained product were analyzed, the distribution of effective strain, temperature and the standardized cracking criterion were determined. The process force parameters were also determined. Numerical tests were verified in real conditions with the use of a specially designed device for forging in vertical split dies. Comparison of hot and cold forging in vertical split dies is presented.

Formability limits by wrinkling in sheet metal forming

2016 ◽  
Vol 232 (8) ◽  
pp. 681-692 ◽  
Author(s):  
JPG Magrinho ◽  
CMA Silva ◽  
MB Silva ◽  
Paulo AF Martins
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Effective Strain ◽  
Stress Triaxiality ◽  
Roll Forming ◽  
Blank Holder ◽  
Flexible Roll ◽  
Plane Compression ◽  
Level Of Understanding

This paper presents a new combined experimental and theoretical methodology for determining the formability limits by wrinkling in sheet metal forming. The methodology is based on the utilization of rectangular test specimens clamped along its narrower sides and compressed lengthwise and is aimed at replicating the physics behind the occurrence of wrinkling in deformation regions submitted to in-plane compression along one direction. The methodology draws from a previous development in the field of flexible roll forming, and the overall objectives are to enhance and improve its methods and procedures and to provide a new level of understanding on the onset of wrinkling in sheet metal forming. Experimentation and finite element modelling of cylindrical deep-drawing without blank holder combined with the utilization of the space of effective strain vs. stress triaxiality are employed to discuss the applicability and validity of the new proposed methodology for determining the formability limits by wrinkling.

Failure Strain Criterion Accounting for the Effect of Material Strength

2021 ◽  
Author(s):  
N. Baghous ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Ultimate Strength ◽  
Failure Criterion ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
High Strength Steels ◽  
Local Failure ◽  
Material Strength ◽  
Lode Parameter ◽  
Steel Grades

Abstract The objective of this study is to investigate the effect of the Lode parameter on different material strengths. Recent work has shown that ductile failure highly depends on the stress state characterized by both the stress triaxiality T and the Lode parameter L, which is related to the third deviatoric stress invariant. Thus, for six different steel grades, two different specimen geometries were manufactured to account for two different Lode parameters (L = −1 and L = 0), whereas T is controlled by introducing different sized notches at the center of the specimens. By performing tensile experiments and running finite element simulations, the ductile failure loci of the six materials showed variations between the two specimen geometries, indicating that the failure highly depends on the stress state characterized by both T and L. This indicates the need to reassess the ductile local failure criterion in the ASME codes that only accounts for T as a stress state measure. A Lode sensitivity parameter LS is defined based on the experimental results and revealed that the steel grades with ultimate strength higher than a certain threshold value (450 MPa) exhibit sensitivity to the Lode parameter, and the results showed that the LS increases with increase in the ultimate strength of the steel grade. The results were incorporated to enhance the original ASME local failure criterion by accounting for T, L, and LS to accurately assess ductile failure in high-strength steels.

Ring Specimen Geometry for Determining the Ductility of Tubulars

2016 ◽  
Author(s):  
M. A. Al Khaled ◽  
I. Barsoum
Keyword(s):  
Stress State ◽  
Plane Strain ◽  
Stress Triaxiality ◽  
Ductile Failure ◽  
Pressure Vessels ◽  
Ring Specimen ◽  
Lode Parameter ◽  
Wide Range ◽  
Failure Locus

Pressure vessels designed in accordance with the ASME BPVC code are protected against local ductile failure. Recent work has shown that local ductile failure highly depends on the stress state characterized by both stress triaxiality (T) and the Lode parameter (L). In this paper, the effect of stress state on the ductility of a tubular steel is studied. Two ring specimen configurations were optimized to allow the determination of the ductile failure locus of both tensile and plane strain loadings. The geometry of both ring specimen configurations was optimized to achieve a plane strain (L = 0) condition and a generalized tension (L = −1) condition. Notches with different radii were machined on both types to achieve a wide range of stress triaxiality. Specimens were manufactured from SA-106 carbon tubular steel and were tested to determine the ductile failure loci as a function of T and L. Failure locus of SA-106 steel was constructed based on the failure instants and was found to be independent of the variation in the Lode parameter. The ASME-BPVC local failure criterion showed close agreement with experimental results.

Investigation of different inorganic chemical compounds as hot metal forming lubricant by pin-on-disc and hot rolling

2018 ◽  
Vol 125 ◽  
pp. 110-120 ◽  
Author(s):  
Shaogang Cui ◽  
Hongtao Zhu ◽  
Shanhong Wan ◽  
Bach Tran ◽  
Long Wang ◽  
...  
Keyword(s):  
Hot Rolling ◽  
Metal Forming ◽  
Chemical Compounds ◽  
Hot Metal ◽  
Pin On Disc ◽  
Inorganic Chemical

scholarly journals Void closure criteria for hot metal forming: A review

2015 ◽  
Vol 19 ◽  
pp. 239-250 ◽  
Author(s):  
M. Saby ◽  
P.-O. Bouchard ◽  
M. Bernacki
Keyword(s):  
Metal Forming ◽  
Hot Metal ◽  
Void Closure

scholarly journals Experimental and FEM Analysis of Void Closure in the Hot Cogging Process of Tool Steel

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 538 ◽  
Author(s):  
Marcin Kukuryk
Keyword(s):  
Hydrostatic Stress ◽  
Effective Strain ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Fem Analysis ◽  
Experimental Tests ◽  
Reduction Ratio ◽  
Compression Process ◽  
Void Closure ◽  
Axial Defects

In the present study, a new complex methodology for the analysis the closure of voids and a new forging system were developed and tested. The efficiency of the forging parameters and the effective geometric shapes of anvils to improve void closure were determined. A new cogging process provided a complete closure of an ingot’s axial defects, as confirmed by experimental tests. The evolution behavior of these defects with different sizes was investigated during the hot cogging process by means of the professional plastic forming software Deform-3D. A comprehensive procedure was developed using the finite-element method (FEM) for the three-dimensional cogging process and laboratory experimentation to predict the degree of void closure. The hot multi-pass cogging process was used to eliminate void defects in the forgings so as to obtain sound products. In the compression process, the effects of the reduction ratio and forging ratio, the void size, and the types of anvil were discussed to obtain the effective elimination of a void. For the purpose of the assessment of the effectiveness of the void closure process, the following indices were introduced: the relative void volume evolution ratio, the relative void diameter ratio, and the internal void closure evaluation index. Moreover, the void closure process was assessed on the basis of stress triaxiality, hydrostatic stress, forging ratio, value of local effective strain around the void, and critical reduction ratio. The results of this research were complemented by experiments predicting the formation of fractures in the regions near the void and in the volume of the forging in the course of the cogging process. The comparison between the predicted and the experimental results showed a good agreement.

Damage and fatigue analysis of AA7050-T7451 plate with cold expanded hole based on a micro-void evolution model

2019 ◽  
Vol 54 (2) ◽  
pp. 105-115
Author(s):  
Fengmei Xue ◽  
Fuguo Li ◽  
Xiaolei Cui
Keyword(s):  
Fatigue Life ◽  
Fatigue Behavior ◽  
Three Dimensional ◽  
Complex Stress ◽  
Evolution Model ◽  
Fatigue Properties ◽  
Strengthening Effect ◽  
Void Evolution ◽  
Cold Worked ◽  
Three Dimensional Finite Element

The ultimate tensile strength and fatigue life of plate with cold worked hole under high loading are always key designing parameters in engineering field. In this article, different cold expanded degrees (ranging from 1.69% to 11.11%) are applied to plate specimens with a central hole, made of 7050-T7451 aluminum alloy. The damage and fatigue properties are investigated by the three-dimensional finite element method with a user subroutine embedded into a void evolution model under complex stress states. The damage analysis indicates that plastic damage becomes critical when the cold expanded degree is larger than 7.14%, which does not suit for further service due to the loss of toughness. The cold expanded degree of 5.26% is identified as the best. It can be found that the fatigue life improves with the increased cold expanded degree. The small cold expanded degree leads to poor strengthening effect because of lacking sufficient residual stress, while large cold expanded degree makes micro-cracks emerge, which is beneficial to the increase in strengthening. All these results prove that the numerical analysis can accurately predict fatigue behavior of AA7050-T7451 plate based on our proposed approach, which is expected to be a powerful method in engineering field.

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