Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications

2017 ◽  
Vol 232 (11) ◽  
pp. 1994-2008 ◽  
Author(s):  
Zhutao Shao ◽  
Nan Li ◽  
Jianguo Lin ◽  
Trevor A Dean
Keyword(s):  
Error Analysis ◽  
Hot Stamping ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Gauge Length ◽  
Temperature Gradients ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Heating And Cooling ◽  
Gauge Section

In order to conduct uniaxial tensile tests for hot stamping applications, tests are normally performed by using a Gleeble thermo-mechanical materials simulator so that rapid heating and cooling processes can be obtained. However, temperature gradients in a specimen tested on Gleeble are inevitable due to resistance heating principles and heat loss to grips and water-cooled jaws. In this research, a pair of purpose-built grips made of stainless steel with low thermal conductivity and significantly reduced contacting area for clamping, as well as a flat dog-bone specimen with maximised parallel length (80 mm) were designed, for the purpose of improving the temperature uniformity within the concerned gauge section area of the specimen. Uniaxial tensile tests on AA6082 were performed, after controlled heating and cooling processes, at constant deformation temperatures in the range of 400 ℃–500 ℃ and at constant strain rate in the range of 0.1–4/s, to simulate its hot stamping conditions. The digital image correlation system was adopted to enable strain distributions in specimens to be measured. The temperature distributions in specimens were investigated and an effective gauge length of 14 mm was specified accordingly to ensure temperature gradients less than 10 ℃ within it at all tested temperatures. True stress–true strain curves of AA6082 were obtained based on results of strain measurements along the defined effective gauge length and used to calibrate a set of advanced material model. Error analysis was carried out by using thermo-electrical and thermo-mechanical FE models on ABAQUS, in which the calibrated material constitutive equations were implemented via subroutines. The error of stress–strain curves of AA6082 measured based on the specified gauge length was investigated and quantified by analysing the distribution of axial strain and axial stress.

scholarly journals Measurement and Analysis of Heterogeneous Strain Fields in Uniaxial Tensile Tests for Boron Steel Under Hot Stamping Conditions

2020 ◽  
Vol 60 (9) ◽  
pp. 1289-1300
Author(s):  
R. Zhang ◽  
Z. Shao ◽  
J. Lin ◽  
T. A. Dean
Keyword(s):  
Temperature Gradient ◽  
Hot Stamping ◽  
Tensile Tests ◽  
Gauge Length ◽  
Image Correlation ◽  
Effect Of Temperature ◽  
Uniaxial Tensile ◽  
Boron Steel ◽  
Strain Fields ◽  
Dog Bone

Abstract Background A significant amount of uniaxial tensile tests has been carried out using Gleeble systems to investigate the viscoplastic deformation of boron steel (22MnB5) under hot stamping conditions. However, due to heat loss through the end clamps, a temperature gradient in the reduced parallel section of dog-bone shaped specimens is inevitable. Objective In the work reported in this paper, the effect of temperature gradient on measured outcomes is examined. Methods Uniaxial tensile tests on 1.5 mm thick boron steel specimens are carried out, under hot stamping conditions and strain fields are quantified using the digital image correlation (DIC) technique. The effect of gauge length on the properties of boron steel, as calculated from observed test results, is determined. Results Compared with the test at room temperature, a bell-shaped strain distribution occurs within the gauge length even before the appearance of the maximum load. Also, average strain within the gauge length, especially in the later stages, changes with gauge length within the investigated range, and thus, different engineering stress-strain curves and fracture strains are determined. In addition, normalized strain rate is significantly dependent on gauge length, which results in over 16% difference among the computed flow stresses by using a unified constitutive model. Conclusions The characterized properties of the material are dependent on gauge length and thus, a testing standard for measuring thermal-mechanical data of materials by using a Gleeble need to be defined.

Elasto-viscoplastic constitutive equations for the description of glassy polymers behavior at constant strain rate

2006 ◽  
Vol 129 (1) ◽  
pp. 29-35 ◽  
Author(s):  
Fahmi Zaïri ◽  
Moussa Naït-Abdelaziz ◽  
Krzysztof Woznica ◽  
Jean-Michel Gloaguen
Keyword(s):  
Constitutive Equations ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Glassy Polymers ◽  
Uniaxial Tensile ◽  
Model Parameters ◽  
Strain Rates ◽  
State Variable ◽  
Rubber Toughened ◽  
Compressive Tests

In this study, a modelization of the viscoplastic behavior of amorphous polymers is proposed, from an approach originally developed for metal behavior at high temperature, in which state variable constitutive equations have been modified. A procedure for the identification of model parameters is developed through the use of experimental data from both uniaxial compressive tests extracted from the literature and uniaxial tensile tests performed in this study across a variety of strain rates. The numerical algorithm shows that the predictions of this model well describe qualitatively and quantitatively the intrinsic softening immediately after yielding and the subsequent progressive orientational hardening corresponding to the response of two polymers, amorphous polyethylene terephthalate and rubber toughened polymethyl methacrylate.

Functional Gradation in Precipitation Hardenable AA7075 Alloy by Differential Cooling Strategies

2021 ◽  
Vol 883 ◽  
pp. 159-166
Author(s):  
Emad Scharifi ◽  
Moritz Roscher ◽  
Steffen Lotz ◽  
Ursula Weidig ◽  
Eric Jägle ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Phase Particle ◽  
Hot Stamping ◽  
Aging Treatment ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Material Strength ◽  
Second Phase ◽  
Contrast Imaging ◽  
Forming Tools

Inspired by steel forming strategies, this study focuses on the effect of differential cooling on mechanical properties and precipitation kinetics during hot stamping of high strength AA7075 alloy. For this aim, different forming strategies were performed using segmented and differentially heated forming tools to provide locally tailored microstructures. Upon processing, uniaxial tensile tests and hardness measurements were used to characterize the mechanical properties after the aging treatment. Microstructure investigations were conducted to examine the strengthening mechanisms using the electron channeling contrast imaging (ECCI) technique in a scanning electron microscope (SEM). Based on the obtained results, it can be deduced that the tool temperatures play a key role in influencing the mechanical properties. Lower tool temperatures result in higher material strength and higher tool temperatures in lower mechanical properties. By changing the cooling rate with the use of differently heated forming tools, the mechanical properties can be controlled. Microstructure investigations revealed the formation of very fine and homogeneously distributed particles at cooled zones, which were associated with elevated mechanical properties due to the suppression of second phase particle formation during cooling. In contrast, coarse particles were observed at lower cooling rates, explaining the lower material strength found in these zones.

scholarly journals Feasibility study of a novel hot stamping process for Ti6Al4V alloy

2018 ◽  
Vol 190 ◽  
pp. 08001
Author(s):  
Mateusz Kopec ◽  
Kehuan Wang ◽  
Yaoqi Wang ◽  
Liliang Wang ◽  
Jianguo Lin
Keyword(s):  
Mechanical Properties ◽  
Titanium Alloy ◽  
Phase Transformation ◽  
New Technology ◽  
Hot Stamping ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Ti6al4v Titanium Alloy ◽  
Stamping Process ◽  
Forming Tools

To investigate the feasibility of a novel hot stamping process for the Ti6Al4V titanium alloy using low temperature forming tools, mechanical properties of the material were studied using hot tensile tests at a temperature range of 600 - 900°C with a constant strain rate of 1s-1. Hot stamping tests were carried out to verify the feasibility of this technology and identify the forming window for the material. Results show that when the deformation temperature was lower than 700°C, the amount of elongation was less than 20%, and it also had little change with the temperature. However, when the temperature was higher than 700°C, a good ductility of the material can be achieved. During the forming tests, parts failed at lower temperatures (600°C) due to the limited formability and also failed at higher temperatures (950°C) due to the phase transformation. The post-form hardness firstly decreased with the temperature increasing due to recovery and then increased due to the phase transformation. Qualified parts were formed successfully between temperatures of 750 - 850°C, which indicates that this new technology has a great potential in forming titanium alloys sheet components.

scholarly journals Investigation of diffusion behavior of carburized sheet metal in hot stamping

2019 ◽  
Vol 6 ◽  
pp. 16
Author(s):  
Alexander Horn ◽  
Marion Merklein
Keyword(s):  
Mechanical Properties ◽  
Sheet Metal ◽  
Lightweight Design ◽  
Hot Stamping ◽  
Carbon Diffusion ◽  
Tensile Tests ◽  
Process Window ◽  
Uniaxial Tensile ◽  
Body Parts ◽  
Passenger Safety

Today, manufacturing of structural car body parts faces several challenges, like forming accuracy, passenger safety and lightweight design. One possibility to fulfill these partially rivalling demands is the application of hot stamped components. The combination of hot forming and in-die quenching reduces not only springback, but also results in tensile strengths of more than 1500 MPa. Besides conventional hot stamping, the process can be adapted to manufacture parts with tailored properties. One of the biggest issues of these state-of-the-art processes is the formation of extensive transition zones due to heat transfer. A promising approach to adjust the mechanical properties with a minimized transition zone is tailored carburization of sheet metal. Therefore, the parts are locally coated with graphite, heat treated and subsequently quenched. In this work, the time variant process of carbon diffusion is investigated. Sheets with two different thicknesses are carburized and quenched. The resulting mechanical properties are analyzed using uniaxial tensile tests and microhardness measurements. On this basis, a process window is identified. Furthermore, the applicability of EDX and WDX analysis for the measurement of carbon concentration is investigated within this work.

scholarly journals Investigation of diffusion behavior of carburized sheet metal in hot stamping

2018 ◽  
Vol 190 ◽  
pp. 08004 ◽  
Author(s):  
Alexander Horn ◽  
Marion Merklein
Keyword(s):  
Mechanical Properties ◽  
Transition Zone ◽  
Sheet Metal ◽  
Lightweight Design ◽  
Hot Stamping ◽  
Sheet Thickness ◽  
Carbon Diffusion ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Body Parts

Today’s manufacturing of structural car body parts faces several challenges, like forming accuracy and passenger safety. Besides these two requirements, lightweight design plays an important role. One possibility to fulfill these partially rivalling demands is the application of hot stamped parts. The combination of hot forming and in die quenching reduces not only springback, but also results in tensile strengths of up to 1500 MPa. This makes a simultaneous reduction of sheet thickness and therefore weight reduction possible. Further development enabled a tailored adjustment of mechanical properties, for example by applying different cooling conditions along the parts. One of the biggest issues of these state of the art processes is the formation of a transition zone due to heat transfer. A promising approach to adjust the mechanical properties with a minimized transition zone is the carburization of sheet metal. Therefore, the parts are coated with graphite, heat treated and subsequently quenched. In this work, the time variant process of carbon diffusion is investigated. Sheets with two different thicknesses are carburized and quenched. The resulting mechanical properties are analyzed using uniaxial tensile tests and microhardness measurements. The results are correlated with the carbon content measured by EDX-analysis.

scholarly journals Strain Distribution of Intact Rat Rotator Cuff Tendon-to-Bone Attachments and Attachments With Defects

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Ryan C. Locke ◽  
John M. Peloquin ◽  
Elisabeth A. Lemmon ◽  
Adrianna Szostek ◽  
Dawn M. Elliott ◽  
...  
Keyword(s):  
Area Under The Curve ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Defect Group ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Transverse Strain ◽  
Intact Group ◽  
Deformation Patterns ◽  
Insight Into

Abstract This study aimed to experimentally track the tissue-scale strains of the tendon–bone attachment with and without a localized defect. We hypothesized that attachments with a localized defect would develop strain concentrations and would be weaker than intact attachments. Uniaxial tensile tests and digital image correlation were performed on rat infraspinatus tendon-to-bone attachments with defects (defect group) and without defects (intact group). Biomechanical properties were calculated, and tissue-scale strain distributions were quantified for superior and inferior fibrous and calcified regions. At the macroscale, the defect group exhibited reduced stiffness (31.3±3.7 N/mm), reduced ultimate load (24.7±3.8 N), and reduced area under the curve at ultimate stress (3.7±1.5 J/m2) compared to intact attachments (42.4±4.3 N/mm, 39.3±3.7 N, and 5.6±1.4 J/m2, respectively). Transverse strain increased with increasing axial load in the fibrous region of the defect group but did not change for the intact group. Shear strain of the superior fibrous region was significantly higher in the defect group compared to intact group near yield load. This work experimentally identified that attachments may resist failure by distributing strain across the interface and that strain concentrations develop near attachment defects. By establishing the tissue-scale deformation patterns of the attachment, we gained insight into the micromechanical behavior of this interfacial tissue and bolstered our understanding of the deformation mechanisms associated with its ability to resist failure.

scholarly journals Thermomechanical response of Mg AZ31 at different levels of temperatures and strain rates

2019 ◽  
Vol 304 ◽  
pp. 01025
Author(s):  
Farid Abed ◽  
Wael Abuzaid ◽  
Yomna Morad
Keyword(s):  
True Strain ◽  
Weight Ratio ◽  
High Strength ◽  
Tensile Tests ◽  
Industrial Applications ◽  
Gauge Length ◽  
Image Correlation ◽  
Strain Rates ◽  
Localized Deformation ◽  
The Difference

Magnesium alloys’ mechanical behavior has received increasing attention because of its high strength to weight ratio making them ideal for various industrial applications, such as vehicle components, transportation and aerospace. The objective of this work is to closely investigate the thermo-mechanical properties of magnesium alloy AZ31 at different strain rates and temperatures. Tensile tests are conducted on a 30 mm gauge length MgAZ31 specimens at two quasi-static strain rates (1.11x10−3 s−1 and 0.28 s−1) at a range of temperatures between 25 ºC and 250 ºC. Digital Image Correlation (DIC) system was used to calculate the true strain and provide quantitative assessment of the localized deformation response at high levels of deformation. The stress-strain responses of MgAZ31 show that the yield stress as well as the ultimate stress decreases as temperature increases and strain rate decreases. Moreover, the difference between the yield and ultimate stresses at both strain rates increases rapidly as temperature increases. The material shows a significant increase in ductility as temperature increases while the modulus of elasticity remains independent of change in strain rates.

Investigation on the Strain Behaviour of a Precipitation-Hardenable Aluminium Alloy through a Temperature Gradient Based Heat Treatment

2015 ◽  
Vol 639 ◽  
pp. 361-368 ◽  
Author(s):  
Gabriella di Michele ◽  
Pasquale Guglielmi ◽  
Gianfranco Palumbo ◽  
Donato Sorgente
Keyword(s):  
Heat Treatment ◽  
Temperature Gradient ◽  
Aluminium Alloy ◽  
Room Temperature ◽  
Tensile Tests ◽  
Gauge Length ◽  
Image Correlation ◽  
Experimental Campaign ◽  
Strain Behaviour ◽  
Heat Treated

In this work the strain behaviour of the heat-treated 6xxx series aluminium alloy AC170PX is investigated by a not conventional approach. Thanks to the low density combined with good mechanical properties, this aluminium alloy is often adopted for automotive applications. Despite these advantages, its formability at room temperature is low. In order to overcome this limit, a distribution of the material properties can be achieved by a local heat treatment (Tailored Heat Treated Blanks). In this context, to evaluate the effects of those parameters mainly affecting the precipitation hardening (aging temperature and aging time), a first experimental campaign was conducted using conventional furnace heat treatment in different conditions . Tensile tests were run with the aim of determining the flow and the aging curves of the heat treated specimens. Starting from these results, a not uniform heat treatment was designed using a Gleeble physical simulator Heat treatments based on a temperature gradient along the sample were performed. Then, tensile tests of the so heated specimens were carried out at room temperature. Through a digital image correlation system both the distribution and the evolution of the strain along the gauge length of the specimen were analysed in order to obtain the hardening/softening working conditions related to a specific heating cycle. These results were validated by the comparison with the data obtained from the first experimental campaign.

scholarly journals Study on Retrofitted Masonry Elements under Shear Using Digital Image Correlation

Sensors ◽  
2020 ◽  
Vol 20 (7) ◽  
pp. 2122 ◽  
Author(s):  
Benjamín Torres ◽  
Francisco B. Varona ◽  
F. Javier Baeza ◽  
David Bru ◽  
Salvador Ivorra
Keyword(s):  
Digital Image Correlation ◽  
Mechanical Behavior ◽  
Digital Image ◽  
Tensile Tests ◽  
Shear Behavior ◽  
Wind Pressure ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Tension Tests ◽  
Reinforced Masonry

Architectural heritage is usually built with masonry structures, which present problems under lateral in-plane loading conditions, such as wind pressure or earthquakes. In order to improve the shear behavior of masonry, the use of a fabric-reinforced cementitious matrix (FRCM) has become an interesting solution because of its synergy of mechanical properties and compatibility with masonry substrates. For a proper structural evaluation, the mechanical behavior of reinforced masonry and the FRCM itself needs to be characterized. Hence, a numerical model to evaluate the FRCM reinforcement requires some mechanical parameters that may be difficult to obtain. In this sense, the shear behavior of masonry can be evaluated by means of diagonal tension tests on small specimens (71 × 71 cm). In this work, a digital image correlation (DIC) monitoring system was used to control displacements and cracking patterns of masonry specimens under shear stress (induced by diagonal tension with FRCM layers) applied to one or two sides. In addition, the mechanical behavior of FRCM coupons under uniaxial tensile tests was also registered with DIC. The displacement measurements obtained by DIC were validated with the measurements registered with LVDT. Unlike LVDT-based techniques, DIC monitoring allowed us to measure deformations in masonry during the full test, detecting crack initiation even before it was visible to the eye.

Sign in / Sign up

Export Citation Format

Share Document