Numerical Simulation of Perforated Hollow Sphere Structures (PHSS) to Investigate Mechanical Properties

2009 ◽  
Vol 620-622 ◽  
pp. 275-278 ◽  
Author(s):  
Andreas Öchsner ◽  
Seyed Mohammad Hossein Hosseini ◽  
Markus Merkel
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Yield Stress ◽  
Elastic Properties ◽  
Hollow Sphere ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Inner Sphere ◽  
New Type

This paper investigates the uniaxial mechanical properties of a new type of hollow sphere structures. For this new type, the sphere shell is perforated by several holes in order to open the inner sphere volume and surface. The mechanical properties, i.e. elastic properties and initial yield stress, of perforated hollow sphere structures in a primitive cubic arrangement are numerically evaluated for different hole diameters and different sphere wall thicknesses.

A Modified Peric Model for Al-Mg Alloy Sheet with Rate-Independent Initial Yield Stress at Warm Temperatures

2019 ◽  
Vol 287 ◽  
pp. 3-7
Author(s):  
Yong Zhang ◽  
Qing Zhang ◽  
Yuan Tao Sun ◽  
Xian Rong Qin
Keyword(s):  
Flow Stress ◽  
Plastic Strain ◽  
Strain Rate ◽  
Yield Stress ◽  
Constitutive Models ◽  
Mg Alloy ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Rate Dependent ◽  
Dependent Flow

The constitutive modeling of aluminum alloy under warm forming conditions generally considers the influence of temperature and strain rate. It has been shown by published flow stress curves of Al-Mg alloy that there is nearly no effect of strain rate on initial yield stress at various temperatures. However, most constitutive models ignored this phenomenon and may lead to inaccurate description. In order to capture the rate-independent initial yield stress, Peric model is modified via introducing plastic strain to multiply the strain rate, for eliminating the effect of strain rate when the plastic strain is zero. Other constitutive models including the Wagoner, modified Hockett–Sherby and Peric are also considered and compared. The results show that the modified Peric model could not only describe the temperature-and rate-dependent flow stress, but also capture the rate-independent initial yield stress, while the Wagoner, modified Hockett–Sherby and Peric model can only describe the temperature-and rate-dependent flow stress. Moreover, the modified Peric model could obtain proper static yield stress more naturally, and this property may have potential applications in rate-dependent simulations.

Simulation of the Impact Behaviour of Diffusion-Bonded and Adhered Perforated Hollow Sphere Structures (PHSS)

2009 ◽  
Vol 294 ◽  
pp. 27-38 ◽  
Author(s):  
Fabian Ferrano ◽  
Marco Speich ◽  
Wolfgang Rimkus ◽  
Markus Merkel ◽  
Andreas Öchsner
Keyword(s):  
Mechanical Properties ◽  
Finite Element Method ◽  
Finite Element ◽  
Mechanical Behaviour ◽  
Hollow Sphere ◽  
Large Deformations ◽  
The Finite Element Method ◽  
Impact Behaviour ◽  
New Type ◽  
The Impact

This paper investigates the mechanical properties of a new type of hollow sphere structure. For this new type, the sphere shell is perforated by several holes in order to open up the inner sphere volume and surface. The mechanical behaviour of perforated sphere structures under large deformations and strains in a primitive cubic arrangement is numerically evaluated by using the finite element method for different hole diameters and different joining techniques.

Numerical Simulation of Thermal and Mechanical Properties of Sintered Perforated Hollow Sphere Structures (PHSS)

2009 ◽  
Author(s):  
Andreas Öchsner ◽  
Seyed Mohammad Hossein Hosseini ◽  
Markus Merkel ◽  
Sio-Iong Ao ◽  
Alan Hoi-Shou Chan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Hollow Sphere ◽  
Thermal And Mechanical Properties

Sensitivity Analysis of Material Parameters on Spring-Back of NC Bending of High-Strength TA18 Tube

2012 ◽  
Vol 472-475 ◽  
pp. 1003-1008 ◽  
Author(s):  
Pei Pei Zhang ◽  
Mei Zhan ◽  
Tao Huang ◽  
He Yang
Keyword(s):  
Elastic Modulus ◽  
Strain Hardening ◽  
Yield Stress ◽  
Strain Hardening Exponent ◽  
Spring Back ◽  
Initial Yield Stress ◽  
Material Parameters ◽  
Strength Coefficient ◽  
Initial Yield ◽  
Nc Bending

Spring-back is one of the key factors affecting the forming quality of the NC bending of high-strength TA18 tubes (TA18-HS tubes). Since material parameters have a direct influence on stress and strain fields during the bending and after unloading, the springback of TA18-HS tubes after NC bending depends on material properties to a great degree. In order to study the effect of material parameters, the sensitivity of material parameters on spring-back of TA18-HS tubes is analyzed in this study, using the numerical simulation and the multi-parameters sensitivity analysis method. The results show the following: (1) The springback angle has a positive correlation with the strength coefficient and initial yield stress, and has a negative correlation with the elastic modulus and strain hardening exponent. Besides, with the increase of elastic modulus, the fluctuation of springback goes gently; with the increase of the strength coefficient and initial yield stress, the fluctuation of springback goes abruptly; but with the variation of the strain hardening exponent, the springback fluctuates slightly; (2) The elastic modulus is the most sensitive material parameter on spring-back, the strength coefficient and initial yield stress rank the second and third, respectively, and the strain hardening exponent is the last. The achievement of the study is valuable to eliminate the non-sensitivity parameters, simplify the optimization project, and improve the spring-back prediction capability.

Analysis of the Electric and Thermal Effects on Mechanical Behavior of SS304 Subjected to Electrically Assisted Forming Process

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Tianhao Jiang ◽  
Linfa Peng ◽  
Peiyun Yi ◽  
Xinmin Lai
Keyword(s):  
Thermal Effect ◽  
Electric Current ◽  
Yield Stress ◽  
Additional Stress ◽  
Forming Process ◽  
Activation Effect ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Electrically Assisted ◽  
Tension Tests

Significant improvements in deformation resistance and ductility of metals are observed in the electrically assisted forming (EAF) process. Both electroplastic effect (EPE) induced by electric current and thermal effect associated with Joule heating have been proposed to explain the phenomenon. However, there are still arguments in the contribution of the EPE in EAF process. In this paper, both electrically assisted tension tests (EAT) and thermally assisted tension tests (TAT) were conducted on SS304 specimens at the same temperature. The existence of EPE is investigated, and the contribution of EPE is also distinguished with thermal effect numerically by considering the initial yield stress, dislocation hardening, and martensite phase transformation. It is shown when the temperature is around 34 °C, the electric current of 50 A/mm2 in EAT induces additional stress reduction of 16% in the short-range internal stress (effective stress) involved in the initial yield stress and volume reduction of 45.2% in martensite formation compared with results in TAT. However, the effect is not obvious for the cases of 100 A/mm2 and 150 A/mm2 when the temperature is above 100 °C. By comparing the storage coefficient and recovery coefficient of dislocation in EAT and TAT, it indicates that electric current has no additional activation effect on dislocation movement of SS304.

Increasing Initial Yield Stress at Small Length Scales

2003 ◽  
Vol 778 ◽  
Author(s):  
I. Spary ◽  
A.J. Bushby ◽  
N.M. Jennett ◽  
G.M. Pharr
Keyword(s):  
Yield Stress ◽  
Size Effects ◽  
Strain Curve ◽  
Compression Tests ◽  
Small Length ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Length Scales ◽  
Initial Yield Stress ◽  
Initial Yield

AbstractPlasticity size effects are well known in a wide variety of situations where either the material microstructure or a strain gradient exist at small length scales. Several theories have been developed to describe changes in the work hardening behaviour under these conditions but none that predict a change in the initial yield stress. Careful studies by Chaudhri et al and Pharr et al have unambiguously demonstrated plasticity size effects in ductile metals. In those experiments indentation stress-strain curves were generated using spherical indenters with radii ranging from a few micrometres to several hundred micrometres and these were compared to data from conventional compression tests. Large radius indenters produced a single indentation stress-strain curve independent of indenter radius with a power law hardening coefficient equivalent to that in the compression tests. However, the indentation stress-strain curves appeared at progressively higher pressures for smaller radius indenters. In this paper we model those experiments using finite element analysis methods. By inputting the uniaxial stress-strain data to the model (effectively, using von Mises criterion) the indentation stress-strain curves for the macro size indenters are reproduced. However, the model shows no length scale dependence for any size of indenter. We show that by off-setting the compression stress-strain curve by increasing the initial yield stress and inputting this data to the model, the indentation behaviour of the smaller radius indenters can be modelled. The increase in yield stress with decreasing indenter radius is demonstrated for Cu, Wand Ir and is shown to be consistent with the initiation of yielding over a finite volume.

scholarly journals A Note on the Kelvin Effect in 100Cr6 Steel with Application to Identification of the Elastoplastic Limit

2012 ◽  
Vol 2012 ◽  
pp. 1-4
Author(s):  
Håkan Hallberg
Keyword(s):  
Yield Stress ◽  
Material Behavior ◽  
Maximum Temperature ◽  
Temperature Decrease ◽  
Strain Measure ◽  
Initial Yield Stress ◽  
Initial Yield ◽  
Heat Treated ◽  
Inelastic Material ◽  
Inelastic Dissipation

Experimental and analytical results are presented regarding the temperature evolution in 100Cr6 steel under uniaxial loading. Differently heat-treated conditions of the material are studied at different strain rates. In the annealed state, the materials exhibits a pronounced initial yield stress as it passes from the elastic region to the plastic through discontinuous yielding. In contrast, the quenched and tempered material yields continuously. The focus of the paper is on the temperature decrease during elastic deformation that precedes the more pronounced heating due to inelastic dissipation once the elastoplastic limit stress is surpassed. The applicability of the maximum temperature decrease in the elastic regime as a replacement for the commonly used 0.2%-strain measure to define the elastoplastic limit is discussed. For 100Cr6 steel, the 0.2%-strain measure is found, in some cases, to overestimate the initial yield stress by 50 MPa. The drop in temperature corresponding to the shift from elastic to inelastic material behavior is experimentally determined and compared to predictions by the Kelvin formula which in the current study give a maximum 50% error.

Deformation of Small Volumes of Material Studied Using Strained-Layer Superlattice Structures

2003 ◽  
Vol 778 ◽  
Author(s):  
K.M.Y. P'ng ◽  
A.J. Bushby ◽  
D.J. Dunstan
Keyword(s):  
Yield Stress ◽  
Finite Volume ◽  
Internal Stresses ◽  
Strained Layer ◽  
Initial Yield Stress ◽  
Semiconductor Superlattice ◽  
Initial Yield ◽  
Strained Layer Superlattice ◽  
Superlattice Structures ◽  
Strained Layer Superlattices

AbstractMechanical studies of semiconductor superlattices have shown that the onset of plastic deformation under an inhomogeneous stress is a process that takes place simultaneously across a finite volume of the order of a micron across. The ability to incorporate known internal stresses, and to vary the stress and thickness of individual layers in a semiconductor superlattice, is a very powerful tool, opening up new possibilities for investigations that cannot be achieved by varying external stresses on a specimen that is sensibly homogeneous. In this way, from the initial yield stress of single-crystal strained-layer superlattices under indentation, we demonstrated a new criterion, of which the key feature is that it is to be averaged over a finite volume. Here we show that designing samples with individual layers in bands to form low yield-stress material within the structure can give information about the size and position of the initial yield volume.

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