An Engineering Approach to Strain Rate and Temperature Compensation of the Flow Stress Established by the Hydraulic Bulge Test

2015 ◽  
Vol 651-653 ◽  
pp. 138-143 ◽  
Author(s):  
J. Mulder ◽  
Henk Vegter ◽  
A.H. van den Boogaard
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Thickness Distribution ◽  
Accurate Determination ◽  
Plastic Work ◽  
Bulge Test ◽  
Hydraulic Bulge Test ◽  
Hydraulic Bulge ◽  
Steel Grades ◽  
Optical Strain

Optical measuring systems enable a very accurate determination of the flow stress for the hydraulic bulge test. The flow stress is strain rate and temperature dependent and for the description of work hardening an approximation of the temperature during the test is required. Measuring the temperature during the test usually interferes with the optical strain measurement. A model for the temperature distribution on the bulged surface is developed based on heat generated by plastic work, convection to air on the outer surface, conduction to the tools at the die diameter and conduction to oil on the inside. The plastic work is derived from an approximation of the shape of the bulged surface and an approximation for the thickness distribution, starting from the initial thickness at the die ring to the established thickness at the pole, making use of volume conservation for the bulged sheet. The parameters of the model are tuned to bulge test temperature measurements of four different steel grades using a thermo couple at the pole. The results of the analytical temperature model are in good agreement with the measurements.

Flow Stress Determination of Steel Tube for Hydroformability Evaluation

2012 ◽  
Vol 622-623 ◽  
pp. 656-660
Author(s):  
P. Boonpuek ◽  
S. Jirathearanat ◽  
N. Depaiwa
Keyword(s):  
Flow Stress ◽  
Analytical Model ◽  
Effective Stress ◽  
Steel Tube ◽  
Bulge Test ◽  
Stress Strain ◽  
Contact Points ◽  
Hydraulic Bulge Test ◽  
Hydraulic Bulge ◽  
Internal Pressures

This study aims to determine flow stress of a steel tube by using hydraulic bulge test. A new proposed analytical model for analyzing bulge shapes of hydroformed tubes is postulated. Bulge test apparatus designed using FEA simulation of hydroforming and STKM 11A steel tubes are used in the hydraulic bulge test. Bulge heights and internal pressures are measured during bulge testing. Tube thicknesses at vertex of a bulge shape are measured by a dial caliper gauge. Bulge curvatures and contact points are measured by taking digital photos of bulge shapes combined with measurement methods in CAD software. Effective stress - strain relationships are obtained from the newly developed analytical model using those measured values. Flow stress curves obtained from the effective stress – strain relationships are compared with those by other researchers and tensile test. Finite element analysis methods are used to conduct simulation of tube hydroforming using the flow stress curves. Predicted internal pressures versus bulge heights and tube thicknesses are compared with experimental results. Verification of the developed analytical model is presented. The flow stress at neck point of formed tube is determined.

Flow Stress Curves Using New Volume Measurement Method For Hydraulic Bulge Test

2007 ◽  
Author(s):  
L. M. Smith ◽  
Y. Hadad ◽  
R. Thotakura ◽  
S. Gunala ◽  
S. Manthipragada
Keyword(s):  
Flow Stress ◽  
Measurement Method ◽  
Volume Measurement ◽  
Bulge Test ◽  
Hydraulic Bulge Test ◽  
Hydraulic Bulge

Estimation of Fracture Toughness JIC by Miniature Specimen Hydraulic Bulge Test

2017 ◽  
Vol 898 ◽  
pp. 753-757
Author(s):  
Le Le Gui ◽  
Tong Xu ◽  
Bin An Shou ◽  
Han Kui Wang ◽  
Jing Xiang
Keyword(s):  
Fracture Toughness ◽  
Fracture Energy ◽  
Fracture Strain ◽  
Bulge Test ◽  
Miniature Specimen ◽  
Hydraulic Bulge Test ◽  
Hydraulic Bulge ◽  
Resistance Curves ◽  
Miniature Specimens ◽  
Load Deflection Curve

The fracture toughness tests and a new miniature specimen technology named hydraulic bulge test (HBT) of 3Cr1Mo1/4V at four service time were carried out. Four J-R resistance curves by single-specimen method with one inch CT specimens were obtained to compute the JIC. Different definitions of equivalent fracture strain according to the section morphologies of HBT testing specimens were compared, and fracture energy of miniature specimens with three different thicknesses (0.4mm, 0.5mm and 0.6mm) were also calculated. Results showed that the typical HBT load-deflection curve can be divided into four sections like SPT curve. Equivalent fracture strain and fracture energy EHB can be chosen as two fracture parameters for the HBT specimen. Ductile fracture toughness JIC can be related approximately linearly to both the equivalent fracture strain and fracture energy EHB.

Hydraulic Bulge Test of Electrodeposited Copper Foil

1999 ◽  
Vol 77 (2) ◽  
pp. 55-59 ◽  
Author(s):  
H. D. Merchant ◽  
M. G. Rozboril
Keyword(s):  
Copper Foil ◽  
Bulge Test ◽  
Hydraulic Bulge Test ◽  
Hydraulic Bulge

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.

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