scholarly journals Experimental and Numerical Investigation of Forming Limit Differences in Biaxial and Dome Test

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Chetan P. Nikhare
Keyword(s):  
Contact Pressure ◽  
Material Behavior ◽  
Dome Height ◽  
Forming Limit ◽  
Bulge Test ◽  
Biaxial Test ◽  
Multiaxial Stress ◽  
Sample Geometry ◽  
Biaxial Tests ◽  
Stress States

For centuries, metals and materials have been characterized using a traditional method called a uniaxial tension test. The data acquired from this test found to be adequate for operations of simple forming where one axis stretching is dominant. Currently, due to the demand of lightweight component production, multiple individual parts eliminated by stamping a single complex shape, which also further reduces many secondary operations. This change is driving by the new fuel-efficiency requirement by corporate average fuel economy of 55.8 miles per gallon by 2025.1 Due to complex part geometry, this forming method induces multiaxial stress states, which are difficult to predict using conventional tools. Thus, to analyze these multiaxial stress states limiting dome height tests and bulge tests were recommended in many research publications. However, these tests limit the possibilities of applying multiaxial loading and rather a sample geometry changes are required to imply multiaxial stresses. Even this capability is not an option in bulge test due to leakage issue. Thus, a test machine called a biaxial test was devised that would provide the capability to test the specimen in multiaxial stress states by varying the independent load or displacement on two independent axis. In this paper, two processes, limiting dome tests and biaxial tests were experimented, modeled, and compared. For the biaxial tests, a cruciform test specimen was utilized, and conventional forming limit specimens were used for the dome tests. Variation of sample geometry in limiting dome test and variation of loading in biaxial test were utilized to imply multiaxial stress states in order to capture the limit strain from uniaxial to equibiaxial strain mode. In addition, the strain path, forming, and formability investigated and the differences between the tests provided. From the results, it was noted that higher limit strains were acquired in dome tests than in biaxial tests due to contact pressure from the rigid punch. The literature shows that the contact pressure (which occurs when the rigid tool contacts the deformed body), increases the deformation and thus increases the limit strains to failure. This contact pressure parameter is unavailable in biaxial test, and thus, a pure material behavior can be obtained. However, limit strains from biaxial test cannot be considered for a process where rigid tool is processing the metal, and thus, calibration is necessary.

scholarly journals Forming Limit Differences in Hemispherical Dome and Biaxial Test During Equibiaxial Tension on Cruciform

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Chetan P. Nikhare ◽  
Emmett Vorisek ◽  
John R. Nolan ◽  
John T. Roth
Keyword(s):  
Test Data ◽  
Testing Machine ◽  
Biaxial Stress ◽  
Dome Height ◽  
Forming Limit ◽  
Bulge Test ◽  
Biaxial Test ◽  
Biaxial Testing ◽  
Hemispherical Dome ◽  
Biaxial Tests

Traditionally, the mechanical properties of materials have been characterized using the uniaxial tension test. This test is considered adequate for simple forming operations where single axis loading is dominant. Previous studies, however, have noted that the data acquired from this type of testing are not enough and additional details in other axes under simultaneous deformation conditions are important. To analyze the biaxial strain, some studies have suggested using the limiting dome height test and bulge test. However, these tests limit the extent of using multi-axial loading and the resulting stress pattern due to contact surfaces. Therefore, researchers devised the biaxial machine which is designed specifically to provide biaxial stress components using multiple and varying loading conditions. The idea of this work is to evaluate the relationship between the dome test data and the biaxial test data. For this comparison, cruciform specimens with a diamond shaped thinner gage in the center were deformed with biaxial stretching on the biaxial testing machine. In addition, the cruciform specimens were biaxially stretched with a hemispherical punch in a conventional die-punch setting. Furthermore, in each case, the process was simulated using a three-dimensional (3D) model generated on abaqus. These models were then compared with the experimental results. The forces on each arm, strain path, forming, and formability were analyzed. The differences between the processes were detailed. It was found that biaxial tests eliminated the pressurization effect which could be found in hemispherical dome tests.

Analysis of Forming Limits in Biaxial and Dome Test

2017 ◽  
Author(s):  
Chetan P. Nikhare
Keyword(s):  
Axial Stress ◽  
Axial Loading ◽  
Dome Height ◽  
Forming Limit ◽  
Bulge Test ◽  
Test Machine ◽  
Biaxial Test ◽  
Complex Part ◽  
Single Complex ◽  
Stress States

From centuries the metals and materials has been characterized using a traditional method called uniaxial tension test. The data acquired from this test found adequate for operations of simple forming where one axis stretching is dominant. Currently due to the demand of lightweight component production, multiple individual parts are eliminated by stamping in a single complex shape which further reduces many secondary operation. This need is driven by the requirement of 54 miles per gallon by 2025. Due to the complex part geometry, the forming method induces multi-axial stress states, which found difficult to predict using conventional tools. Thus to analyze these multi-axial stress states limiting dome height test and bulge test were recommended in many research. However, these tests limit the possibilities of applying multi-axial loading and resulting stress patterns due to contact surfaces. Thus a test machine called biaxial test is devised which would provide the capability to test the specimen in multi-axial stress states with varying load. In this paper, two processes, limiting dome test and biaxial test were modeled and compared. For this, the cruciform test specimens were used in biaxial test and conventional forming limit specimens for dome test. Variation of loadings were provided multi-axially in both test to capture the limit strain from uniaxial to equi-biaxial strain mode. In addition, the strain path, forming and formability was investigated and difference between the tests were provided.

Understanding the Differences in Hemispherical Dome and Biaxial Test During Equi-Biaxial Tension on Cruciform

2016 ◽  
Author(s):  
Chetan P. Nikhare ◽  
Emmett Vorisek ◽  
John Nolan ◽  
John T. Roth
Keyword(s):  
Sheet Metal ◽  
Test Data ◽  
Biaxial Tension ◽  
Testing Machine ◽  
Biaxial Stress ◽  
Dome Height ◽  
Bulge Test ◽  
Biaxial Test ◽  
Hemispherical Dome ◽  
Biaxial Tests

One metal manufacturing process which uses thousands of processes to trim, stretch, draw, bend etc. under a big umbrella is sheet metal forming. Using heavy equipment, the sheet metal parts are deformed into complex geometries. The complexity in these parts produces multi-axial stress and strain, a state for which it is critical to analyze using conventional tools. Traditionally, the mechanical properties of materials have been characterized using the uniaxial tension test. This test is considered adequate for simple forming operations where single axis loading is dominant. Previous studies, however, have noted that the data acquired from this type of testing is not enough and additional details in other axes under simultaneous deformation conditions are important. To analyze the biaxial strain, some studies have suggested using the limiting dome height test and bulge test. However, these tests limit the extent of using multi-axial loading and the resulting stress pattern due to contact surfaces. Therefore, researchers devised the biaxial machine which is designed specifically to provide biaxial stress components using multiple and varying loading conditions. The idea of this work is to evaluate the relationship between the dome test data and the biaxial test data. For this comparison, cruciform specimens with a diamond shaped thinner gage in the center were deformed with biaxial stretching on the biaxial testing machine. In addition, the cruciform specimens were bi-axially stretched with a hemispherical punch in a conventional die-punch setting. Furthermore, in each case, the process was simulated using a 3D model generated on ABAQUS. These models were then compared with the experimental results. The forces on each arm, strain path, forming and formability was analyzed. The differences between the processes were detailed. It was found that biaxial tests eliminated the pressurization effect which could be found in hemispherical dome tests.

A Comparative Study on Hydraulic Bulge Testing and Analysis Methods

2008 ◽  
Author(s):  
Eren Billur ◽  
Muammer Koc¸
Keyword(s):  
Flow Stress ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Material Behavior ◽  
Biaxial Stress ◽  
Dome Height ◽  
Bulge Test ◽  
Analysis Methods ◽  
Bulge Testing ◽  
Hydraulic Bulge

Hydraulic bulge testing is a material characterization method used as an alternative to tensile testing with the premise of accurately representing the material behavior to higher strain levels (∼70% as appeared to ∼30% in tensile test) in a biaxial stress mode. However, there are some major assumptions (such as continuous hemispherical bulge shape, thinnest point at apex) in hydraulic bulge analyses that lead to uncertainties in the resulting flow stress curves. In this paper, the effect of these assumptions on the accuracy and reliability of flow stress curves is investigated. The goal of this study is to determine the most accurate method for analyzing the data obtained from the bulge testing when continuous and in-line thickness measurement techniques are not available. Specifically, in this study the stress-strain relationships of two different materials (SS201 and Al5754) are obtained based on hydraulic bulge test data using various analysis methods for bulge radius and thickness predictions (e.g., Hill’s, Chakrabarty’s, Panknin’s theories, etc.). The flow stress curves are calculated using pressure and dome height measurements and compared to the actual 3-D strain measurement from a stereo optical and non-contact measurement system ARAMIS. In addition, the flow stress curves obtained from stepwise experiments are compared with the ones from above methods. Our findings indicate that Enikeev’s approach for thickness prediction and Panknin’s approach for bulge radius calculation result in the best agreement with both stepwise experiment results and 3D optical measurement results.

Experimental Investigation on Forming Limit Curve at Elevated Temperature Through Dome and Biaxial Test

2020 ◽  
Author(s):  
Chetan P. Nikhare ◽  
Evan Teculver ◽  
Faisal Aqlan
Keyword(s):  
Air Pollution ◽  
Fuel Consumption ◽  
Axial Stress ◽  
High Strength ◽  
Tension Test ◽  
Forming Limit ◽  
Biaxial Test ◽  
Limit Curve ◽  
Forming Limit Curve ◽  
Stress States

Abstract The characteristics of metal and materials are very important to design any component so that it should not fail in the life of the service. The properties of the materials are also an important consideration while setting the manufacturing parameters which deforms the raw material to give the design shape without providing any defect or fracture. For centuries the commonly used method to characterize the material is the traditional uniaxial tension test. The standard has been created for this test by American Standard for Testing Materials (ASTM) – E8. This specimen is traditionally been used to test the materials and extract the properties needed for designing and manufacturing. It should be noted that the uniaxial tension test uses one axis to test the material i.e., the material is pulled in one direction to extract the properties. The data acquired from this test found enough for manufacturing operations of simple forming where one axis stretching is dominant. Recently a sudden increase in the usage of automotive vehicles results in sudden increases in fuel consumption which results in an increase in air pollution. To cope up with this challenge federal government is implying the stricter environmental regulation to decrease air pollution. To save from the environmental regulation penalty vehicle industry is researching innovation which would reduce vehicle weight and decrease fuel consumption. Thus, the innovation related to light-weighting is not only an option anymore but became a mandatory necessity to decrease fuel consumption. To achieve this target, the industry has been looking at fabricating components from high strength to ultra-high strength steels or lightweight materials. This need is driven by the requirement of 54 miles per gallon by 2025. In addition, the complexity in design increased where multiple individual parts are eliminated. This integrated complex part needs the complex manufacturing forming operation as well as the process like warm or hot forming for maximum formability. The complex forming process will induce the multi-axial stress states in the part, which is found difficult to predict using conventional tools like tension test material characterization. In many pieces of literature limiting dome height and bulge tests were suggested analyzing these multi-axial stress states. However, these tests limit the possibilities of applying multi-axial loading and resulting stress patterns due to contact surfaces. Thus, a test machine called biaxial test is devised which would provide the capability to test the specimen in multi-axial stress states with varying load. In this paper, two processes, limiting dome test and biaxial test were experimented to plot the forming limit curve. The forming limit curve serves the tool for the design of die for manufacturing operation. For experiments, the cruciform test specimens were used in both limiting dome test and biaxial test and tested at elevated temperatures. The forming limit curve from both tests was plotted and compared. In addition, the strain path, forming, and formability was investigated and the difference between the tests was provided.

Influence of Servo Motion on Forming Limit of Thin Metallic Foils Using Micro Bulge Test

2016 ◽  
Vol 716 ◽  
pp. 208-214
Author(s):  
Ryo Yamaguchi ◽  
Tetsuhide Shimizu ◽  
Ming Yang
Keyword(s):  
Grain Size ◽  
Stress Relaxation ◽  
Ultrasonic Vibration ◽  
Forming Limit ◽  
Bulge Test ◽  
Production Methods ◽  
Step Motion ◽  
Stress States ◽  
Metallic Parts ◽  
Metallic Foils

The demand of microforming is increasing as one of the economical production methods for small metallic parts. However, the formability of metallic foils decreases with decreasing ratio of thickness to grain size. In the present study, a process combining step motion and ultrasonic vibration is proposed to enhance the formability by stress relaxation. To investigate the effect of stress relaxation on forming limit of metallic foils in different stress states, micro bulge tests were carried out. The material used was brass foils with a thickness of 0.03, 0.05 and 0.08 mm. For calculating the strains of the deformed specimens, a pattern of dots with a diameter and a pitch of 50 and 60 μm was fabricated on the surface of the specimens by photolithography. The results of micro bulge tests showed that the forming limit increases by the stress relaxation regardless of stress states, except for the foil with a thickness of 0.03 mm. The possibility of enhancing the formability of metallic foils by stress relaxation was experimentally demonstrated.

Investigation of Anisotropy Effect on the Material Properties Obtained from Biaxial Tests

2020 ◽  
Vol 856 ◽  
pp. 128-134
Author(s):  
Chalida Udomraksasakul ◽  
Thanasan Intarakumthornchai ◽  
Yingyot Aue-u-Lan
Keyword(s):  
Flow Stress ◽  
Tensile Test ◽  
Mechanical Test ◽  
Rolling Direction ◽  
Uniaxial Tensile ◽  
Bulge Test ◽  
Uniaxial Tensile Test ◽  
Biaxial Test ◽  
Anisotropy Effect ◽  
Biaxial Tests

Hydraulic bulge test or biaxial test is a well-known mechanical test used to determine a flow stress of material because of the large level of effective strains and not interfered by the necking unlike in uniaxial tensile test. However, the flow stress obtained is influenced by the anisotropy effect. That flow stress needs to be corrected by the anisotropic values (r-values) obtained from the uniaxial tensile test which limited by the necking. Therefore, to obtain the accurate flow stress the r-values should be determined directly from the biaxial test. The elliptical tests with ratio of 2 (the ratio between major and minor axis) at different sheet orientations (0๐ and 90๐ from the rolling direction) and the equibiaxial test were proposed. In this research, the effect of the sheet orientations upon the flow stress (K and n values) under biaxial tests was investigated by experiment and equation of material grade SPCD with the thickness of 0.8mm. The results showed that the flow stress without correcting r-values gave more variations than those with correcting one with the r-values obtained from the uniaxial test. Therefore, the r-values used to correct the flow stress under biaxial test should be directly determined from the biaxial test.

Assessment of Work-Hardening Characteristics and Limit Strains of Anisotropic Aluminum Sheets in Biaxial Stretching

1986 ◽  
Vol 108 (3) ◽  
pp. 250-257 ◽  
Author(s):  
A. R. Ragab ◽  
A. T. Abbas
Keyword(s):  
Work Hardening ◽  
Pure Aluminum ◽  
Material Behavior ◽  
Biaxial Stress ◽  
Forming Limit ◽  
Flow Rule ◽  
Biaxial Test ◽  
Biaxial Stretching ◽  
Aluminum Sheets ◽  
New Material

In this work, commercially pure aluminum sheets in both the as-received and annealed conditions are tested in uniaxial and biaxial tension. Biaxial stretching is performed in dies giving different degrees of stress biaxiality. Resulting effective stresses and plastic strains are estimated according to the original Hill’s theory in the two situations where planar anisotropy is either neglected or taken into consideration. In both situations discrepancies between biaxial and uniaxial flow curves are observed. By analyzing the above uniaxial and biaxial test results according to the flow rule associated with a yield function recently proposed by Hill, a new material index describing the anisotropic behavior has been evaluated. This new material behavior description realized a satisfactory agreement between work-hardening characteristics of the tested aluminum sheets under various biaxial stress systems. The same tested aluminum sheet materials have been then tested in order to determine their forming limit curves. Correlation between these curves and the theoretical predictions of limit strains according to various instability analyses, is sought through the use of the above description of material work-hardening.

scholarly journals Study of biaxial mechanical properties of the passive pig heart: material characterisation and categorisation of regional differences

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Fulufhelo Nemavhola
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Computational Models ◽  
Heart Diseases ◽  
Interventricular Septum ◽  
Model Material ◽  
Biaxial Test ◽  
Material Behaviour ◽  
Material Parameters ◽  
Biaxial Tests

AbstractRegional mechanics of the heart is vital in the development of accurate computational models for the pursuit of relevant therapies. Challenges related to heart dysfunctioning are the most important sources of mortality in the world. For example, myocardial infarction (MI) is the foremost killer in sub-Saharan African countries. Mechanical characterisation plays an important role in achieving accurate material behaviour. Material behaviour and constitutive modelling are essential for accurate development of computational models. The biaxial test data was utilised to generated Fung constitutive model material parameters of specific region of the pig myocardium. Also, Choi-Vito constitutive model material parameters were also determined in various myocardia regions. In most cases previously, the mechanical properties of the heart myocardium were assumed to be homogeneous. Most of the computational models developed have assumed that the all three heart regions exhibit similar mechanical properties. Hence, the main objective of this paper is to determine the mechanical material properties of healthy porcine myocardium in three regions, namely left ventricle (LV), mid-wall/interventricular septum (MDW) and right ventricle (RV). The biomechanical properties of the pig heart RV, LV and MDW were characterised using biaxial testing. The biaxial tests show the pig heart myocardium behaves non-linearly, heterogeneously and anisotropically. In this study, it was shown that RV, LV and MDW may exhibit slightly different mechanical properties. Material parameters of two selected constitutive models here may be helpful in regional tissue mechanics, especially for the understanding of various heart diseases and development of new therapies.

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