A new test for determining the mechanical and fracture behavior of materials in sheet-bulk metal forming

2015 ◽  
Vol 231 (8) ◽  
pp. 693-703 ◽  
Author(s):  
CMA Silva ◽  
MB Silva ◽  
LM Alves ◽  
PAF Martins
Keyword(s):  
Fracture Toughness ◽  
Metal Forming ◽  
Three Dimensional ◽  
Strain Curve ◽  
Shear Zones ◽  
Shear Stresses ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Bulk Metal ◽  
Bulk Metal Forming

This paper presents a new experimental test for determining the stress–strain curve and the fracture toughness of sheets to be used in sheet-bulk metal forming (SBMF) applications. The test is based on the utilization of double-notched specimens loaded in shear and combines the plane stress loading conditions of sheet metal forming with the three-dimensional plastic flow conditions of bulk metal forming, which are commonly found in SBMF processes. The methodology to obtain the stress–strain curve involves calculation of the shear stresses and strains along the two symmetric plastic shear zones of the test specimens up to point where cracks start to propagate along the ligaments that connect each pair of opposite notches. The determination of fracture toughness involves characterization of the evolution of load with displacement for a number of test cases performed with specimens having different ligaments between the two symmetric opposite notches. The work is performed on aluminium alloy EN AW 5754 H111 sheets with 5 mm thickness and the results obtained by means of the new proposed test are compared against those from conventional mechanical and fracture characterization tests.

Stress-strain curve of paper revisited

2012 ◽  
Vol 27 (2) ◽  
pp. 318-328 ◽  
Author(s):  
Svetlana Borodulina ◽  
Artem Kulachenko ◽  
Mikael Nygårds ◽  
Sylvain Galland
Keyword(s):  
Three Dimensional ◽  
Strain Curve ◽  
Failure Behavior ◽  
Three Dimensional Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Fiber Network ◽  
Bonding Parameters ◽  
Particle Level ◽  
The Impact

Abstract We have investigated a relation between micromechanical processes and the stress-strain curve of a dry fiber network during tensile loading. By using a detailed particle-level simulation tool we investigate, among other things, the impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds. This is probably the first three-dimensional model which is capable of simulating the fracture process of paper accounting for nonlinearities at the fiber level and bond failures. The failure behavior of the network considered in the study could be changed significantly by relatively small changes in bond strength, as compared to the scatter in bonding data found in the literature. We have identified that compliance of the bonding regions has a significant impact on network strength. By comparing networks with weak and strong bonds, we concluded that large local strains are the precursors of bond failures and not the other way around.

About Relation Between Irradiation Hardening of Ferritic Steels and Ductile Fracture Toughness Decrease

2009 ◽  
Author(s):  
Jiri Novak
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Ductile Fracture ◽  
Stress Level ◽  
Deformation Theory ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Irradiation Hardening ◽  
Ductile Fracture Toughness

We showed recently that temperature dependence of the ductile fracture toughness can be predicted on the base of two assumptions: 1) assumption of constant characteristic length, 2) assumption of proportionality between J-R curve slope and deformation work in unit volume, evaluated from zero to critical strain for initiation of deformation bands determined in plane strain geometry for material modeled by deformation theory of plasticity. Temperature dependence of ductile fracture toughness results simply from temperature dependence of the stress-strain curve. Irradiation hardening changes stress-strain behavior in a qualitatively different way: It is observed that irradiation hardening to certain yield stress level changes the stress-strain curve of the material in the same way as prestraining of the unirradiated material to the same flow stress level does. Equivalence of irradiation and prestraining concerns all key properties of deformation theory; namely the secant modulus should be taken from the stress-strain curve of unirradiated material. With exception of this specific feature, the task of finding relative fracture toughness decrease by irradiation is the same as prediction of relative decrease of fracture toughness by temperature change. In the frame of the corresponding theory, relative decrease of ductile fracture toughness expressed by J-R curve slope can be obtained from the stress-strain curve of unirradiated material and irradiation hardening level. Quantitative results are presented for the weld metals 72W and 73W, studied in the Fifth Irradiation Series in the Heavy-Section Steel Irradiation Program, and compared with experimental data.

Application of Rigid/Visco-Plastic Element Free Galerkin Method in Three-Dimensional Bulk Metal Forming Processes

2009 ◽  
Vol 419-420 ◽  
pp. 457-460
Author(s):  
Ping Lu ◽  
Xin Wu ◽  
Guo Qun Zhao ◽  
Kai Yong Jiang ◽  
Yan Jin Guan
Keyword(s):  
Galerkin Method ◽  
Metal Forming ◽  
Three Dimensional ◽  
Element Free Galerkin Method ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
Finite Element Software ◽  
Element Free Galerkin ◽  
Plastic Element ◽  
Element Free

Combining element free Galerkin method with rigid/visco-plastic flow theory, the paper establishes the three-dimensional rigid/visco-plastic element free Galerkin method, and introduces it to analyze three-dimensional bulk metal forming processes. The velocity field is approximated by MLS method. Employing the incomplete generalized variation principle, stiffness matrix equation and solution formulas are derived. And STL format discrete triangular patches are used to describe the mould cavity. An analysis program for simulating three-dimensional bulk metal forming processes is developed. The program is capable of simulating three-dimensional unsteady bulk metal forming processes with severe deformation and arbitrarily shaped dies. A numerical example is analyzed. Numerical results such as material flow patterns and distributions of the effective stress are obtained. The effectiveness and validity of the proposed method and techniques are demonstrated by comparing with results obtained by using commercial finite element software.

Trockenumformung strukturierter Halbzeuge aus 16MnCr5 und 42CrMo4*/Dry forming of surface structured workpiece made of 16MnCr5 and 42CrMo4 - Determination of friction shear stress by means of a pin-on-cCylinder Tribometer

2016 ◽  
Vol 106 (10) ◽  
pp. 712-718
Author(s):  
R. Hild ◽  
D. Trauth ◽  
P. Mattfeld ◽  
S. Bastürk ◽  
T. Brögelmann ◽  
...  
Keyword(s):  
Shear Stress ◽  
Metal Forming ◽  
Shear Stresses ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
Dry Forming ◽  
Tool Coatings ◽  
Green Factory

Der Einsatz von Schmierstoffen gestattet bisher die Umformung von Massivbauteilen. In der „Green Factory“ wird auf die Verwendung dieser Schmierstoffe verzichtet. Daraus resultieren unbekannte Anforderungen an das trockene Tribosystem. Selbstschmierende Werkzeugbeschichtung und strukturierte Halbzeuge ermöglichen das trockene Tribosystem und reduzieren die Reibschubspannung. Der Fachbeitrag zeigt die Auswirkungen von Oberflächenstrukturen auf Halbzeugen auf die Reibschubspannung.   Solid and liquid lubricants enable bulk metal forming processes. In the “Green Factory”, the application of lubricants is to be avoided. The absence of lubricants results in unknown demands on a dry tribosystem. Possible enablers of the dry tribosystem are self-lubricating tool coatings and structured workpieces that lower the friction shear stresses. This contribution shows how the workpiece structuring influences the friction shear stress.

scholarly journals Internal shear cracking in bulk metal forming

2016 ◽  
Vol 233 (4) ◽  
pp. 603-614
Author(s):  
P Christiansen ◽  
CV Nielsen ◽  
N Bay ◽  
PAF Martins
Keyword(s):  
Metal Forming ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Propagation Path ◽  
Shear Cracks ◽  
Bulk Metal ◽  
Surface Cracking ◽  
Bulk Metal Forming ◽  
Scope Of Application ◽  
Shear Cracking

This paper presents an uncoupled ductile damage criterion for modelling the opening and propagation of internal shear cracks in bulk metal forming. The criterion is built upon the original work on the motion of a hole subjected to shear with superimposed tensile stress triaxiality and its overall performance is evaluated by means of side-pressing formability tests in Aluminium AA2007-T6 subjected to different levels of pre-strain. Results show that the new proposed criterion is able to combine simplicity with efficiency for predicting the onset of fracture and the crack propagation path for the entire set of test cases regardless the amount of pre-strain derived from previous upsetting under near frictionless conditions. The new proposed criterion can be easily implemented in existing finite element programs and its scope of application allows extending previous work on the opening modes in surface cracking to internal cracks formed under three-dimensional states of stress that are typical of bulk metal forming.

Sheet-Bulk Metal Forming of Symmetric and Asymmetric Parts

2013 ◽  
Vol 769 ◽  
pp. 229-236 ◽  
Author(s):  
Valerian Salfeld ◽  
Richard Krimm ◽  
Sven Hübner ◽  
Thorsten Matthias ◽  
Milan Vucetic
Keyword(s):  
Metal Forming ◽  
Material Flow ◽  
Three Dimensional ◽  
Positive Influence ◽  
Sheet Metals ◽  
Functional Elements ◽  
Bulk Metal ◽  
Bulk Metal Forming ◽  
New Machine

The unique process of sheet-bulk metal forming (SBMF) represents a combination of sheet and bulk metal forming by inducing a three-dimensional material flow in sheet metals in a single forming stage. Within this paper two different applications of sheet-bulk metal forming are demonstrated. Hereby two different combined drawing and upsetting processes to realize parts with symmetrically and asymmetrically arranged functional elements are analysed. Finally, this contribution introduces a new machine technique which provides an improvement of the working accuracy of a forming machine and thus has a positive influence on the parts quality. The idea is to use electromagnetic ram guidance to counteract the displacement of the ram due to horizontal forming forces while forming of asymmetric parts.

scholarly journals Study on the Physical Properties and Joint Evolution Characteristics of Three-Dimensional Reconstructed Coal

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yongning Wu ◽  
Zhe Zhang ◽  
Xinzhe Wang ◽  
Peiyang Zhu ◽  
Xin Yang ◽  
...  
Keyword(s):  
Coal Sample ◽  
Three Dimensional ◽  
Monitoring Program ◽  
Strain Curve ◽  
Joint Surface ◽  
Three Dimensional Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Joint Monitoring ◽  
Joint Evolution

There are various complex joints (fissures), laminae, and other soft structural surfaces in the roadway enclosure, and the existence of these soft structural surfaces seriously affects the stability of the roadway enclosure. In order to study the mechanical properties of the coal body and the development of joints during coal fracture, this paper establishes a three-dimensional model of the fracture structure of the coal body based on CT scanning and three-dimensional reconstruction technology. On this basis, a 3D numerical model of the equivalent nodal coal body is constructed, uniaxial compression simulation analysis is performed, and the joint evolution development law of the coal sample is studied by the built-in joint monitoring program of PFC3D. The results show that the larger the effective joint area and larger the joint size inside the coal sample, the smaller the compressive strength of the coal sample. The increase of joint size and joint surface area increased the ductility and stress-strain curve multipeak phenomenon of the coal sample to some extent. During the rupture of the coal sample, the changes of each phase of the statistical curve of joint number and the phases of the stress-strain curve of the coal sample are compatible.

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