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 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.

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.

scholarly journals Corneal Biomechanical Properties after FS-LASIK with Residual Bed Thickness Less Than 50% of the Original Corneal Thickness

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Haixia Zhang ◽  
Muhammad Ahmad Khan ◽  
Di Zhang ◽  
Xiao Qin ◽  
Ding Lin ◽  
...  
Keyword(s):  
Elastic Moduli ◽  
Corneal Thickness ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Uniaxial Tensile ◽  
Stress Region ◽  
Bed Thickness ◽  
Limit Stress ◽  
The Right ◽  
Corneal Biomechanical Properties

Background. The changes in corneal biomechanical properties after LASIK remain an unknown but important topic for surgical design and prognostic evaluation. This study aims to observe the postoperative corneal biomechanical properties one month after LASIK with amount of corneal cutting (ACC) greater than 50% of the central corneal thickness (CCT). Methods. FS-LASIK was performed in 10 left rabbit eyes with ACC being 60% (L60) and 65% (L65) of the CCT, while the right eyes (R) were the control. After 4 weeks, rabbits were executed and corneal strip samples were prepared for uniaxial tensile tests. Results. At the same strain, the stresses of L65 and L60 were larger than those of R. The elastic moduli of L60 and L65 were larger than those of R when the stress was 0.02 MPa, while they began to be less than those of R when stress exceeds the low-stress region. After 10 s relaxation, the stress of specimens L65, L60, and R increased in turn. Conclusion. The elastic moduli of the cornea after FS-LASIK with ACC greater than 50% of the CCT do not become less under normal rabbit IOP. The limit stress grows with the rise of ACC when relaxation becomes stable.

Finite Element Modeling of Deformation Behavior of Steel Specimens under Various Loading Scenarios

2015 ◽  
Vol 651-653 ◽  
pp. 969-974 ◽  
Author(s):  
Dilip Banerjee ◽  
Mark Iadicola ◽  
Adam Creuziger ◽  
Tim Foecke
Keyword(s):  
Finite Element ◽  
Deformation Behavior ◽  
Stress Measurement ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Fe Model ◽  
Strain Paths

Lightweighting materials (e.g., advanced high strength steels, aluminum alloys etc.) are increasingly being used by automotive companies as sheet metal components. However, accurate material models are needed for wider adoption. These constitutive material data are often developed by applying biaxial strain paths with cross-shaped (cruciform) specimens. Optimizing the design of specimens is a major goal in which finite element (FE) analysis can play a major role. However, verification of FE models is necessary. Calibrating models against uniaxial tensile tests is a logical first step. In the present study, reliable stress-strain data up to failure are developed by using digital image correlation (DIC) technique for strain measurement and X-ray techniques and/or force data for stress measurement. Such data are used to model the deformation behavior in uniaxial and biaxial tensile specimens. Model predictions of strains and displacements are compared with experimental data. The role of imperfections on necking behavior in FE modeling results of uniaxial tests is discussed. Computed results of deformation, strain profile, and von Mises plastic strain agree with measured values along critical paths in the cruciform specimens. Such a calibrated FE model can be used to obtain an optimum cruciform specimen design.

Application of Dic Technique for Monitoring of Deformation Process of Spr Hybrid Joints / Zastosowanie Techniki Dic Do Obserwacji Procesu Deformacji Hybrydowych Połaczen Typu Spr

2013 ◽  
Vol 58 (1) ◽  
pp. 119-125 ◽  
Author(s):  
T. Sadowski ◽  
M. Knec
Keyword(s):  
Deformation Process ◽  
Load Capacity ◽  
Tensile Tests ◽  
Lap Joints ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Specimen Preparation ◽  
Forming Process ◽  
Absorption Increase ◽  
Dic Technique

Digital Image Correlation (DIC) technique gives possibility to observe deformation process in many applications including self-piercing riveting (SPR) hybrid joint. The hybrid SPR joint consists of simple SPR joint made of two adherends, steel tubular rivet (total length of 5 mm) and an adhesive. The adhesive was applied before piercing process. For specimen preparation two different aluminum alloys were used: 2024 and 5005 (2mm thickness both) with tensile strength 400 and 160MPa, respectively. For better understanding of joint forming process and to allow DIC strains observation during the joint creation, a special holder was designed with precisely polished die. The tests were performed by application of the 100kN servo-hydraulic machine, which recorded time, load, displacement and was synchronized with the DIC system. The joint forming process was carried out with 2 mm/min constant speed. During piercing process rivet and upper surface of the adherend were observed and the major strain states were estimated. The uniaxial tensile tests of single lap joints (SLJ) up to the final failure were performed and the displacements and the strains were recorded. In particular the rivet deformation was observed also during the whole loading process. The hybrid SPR joints are very effective, because the load capacity and energy absorption increase more than 1.5 times in comparison to the simple SPR joints.

scholarly journals Process of Identifying Stress Fields from Strain Fields in the Specimen with a Hole

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Michaela Štamborská ◽  
Miroslav Kvíčala ◽  
Vratislav Mareš
Keyword(s):  
Tensile Tests ◽  
Image Correlation ◽  
Stress Fields ◽  
Uniaxial Tensile ◽  
Main Attention ◽  
Identification Procedure ◽  
Complex State ◽  
Strain Fields ◽  
State Of Stress ◽  
Correlation System

The paper is focused on the process of identifying stress fields from strain fields in the specimen with a hole. The experiment was realized on the specimen with a hole made from anisotropic material. The main attention is paid to the analysis of deformation in the areas of stress (near the hole). That geometry generates a heterogeneous strain field which has been measured during the test using a digital image correlation system. The advantage of using heterogeneous strain fields in the identification procedure is that a complex state of stress-strain can be analyzed at the same time. On the other hand the stress field cannot be directly computed from the test and a suitable identification procedure has to be developed. Here, the virtual fields method (VFM) adapted for plastic strain has been used to identify the hardening behaviour and the anisotropy of the material. The values obtained by the VFM have been compared with the results coming from a standard identification made with uniaxial tensile tests.

Consideration of Yield Discontinuity in the Elastic-Plastic Fracture Analysis of Circumferentially Flawed Pipes

2017 ◽  
Author(s):  
Longjie Wang ◽  
Elvin Eren ◽  
Bin Wang ◽  
Guiyi Wu
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Strain Curve ◽  
Tensile Tests ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Stress Plateau ◽  
Crack Driving Force

This study examined the fracture behaviour of pipes containing surface flaws oriented circumferentially and made from a material that exhibits yield discontinuity (known as Lüders plateau) with the view of making recommendations for the assessment of pipes subject to high level of plasticity. Starting with the fundamental and first principles, uniaxial tensile tests were carried out with the use of digital image correlation (DIC) to observe the formation and propagation of Lüders bands quantitatively. Finite element (FE) analyses were then carried out to simulate the Lüders banding phenomenon in uniaxial tensile specimens and consequently cracked pipes. Different material models were adopted in FE analyses, including the stress-strain curve with a flat stress plateau neglecting upper yield stress, and the so-called ‘up-down-up’ (UPU) stress-strain curve for refining crack driving force predictions. The numerical analysis of tensile tests demonstrated that UPU stress-strain model satisfactorily simulated the main macroscopic features of Lüders band observed in the experiment. FE analysis of flawed pipes using both flat and UPU stress-strain curves produced a similar trend in the crack tip opening displacement (CTOD)-strain trajectory as that obtained from large-scale testing. It was seen that the shape of the UPU stress-strain curve, particularly the magnitude of softening, considerably affects the magnitude of crack driving force in the flawed pipe. However, the strain localisation associated with Lüders banding was not observed in the circumferentially flawed pipe in the case of using the flat stress-strain curve. The CTOD crack driving force obtained from simulations was lower than the CTOD obtained from experiments in the Lüders plateau regime, even with the consideration of ductile tearing. Finally, as a result of this study, recommendations on the optimum choice of material parameters were made for more accurate predictions of crack driving force in the presence of yield discontinuity.

Brillouin confocal microscopy to determine biomechanical properties of SULEEI-treated bovine pericardium for application in cardiac surgery

2021 ◽  
pp. 1-14
Author(s):  
Anett Jannasch ◽  
Jan Rix ◽  
Cindy Welzel ◽  
Gabriele Schackert ◽  
Matthias Kirsch ◽  
...  
Keyword(s):  
Confocal Microscopy ◽  
Young’S Modulus ◽  
Heart Valve ◽  
Acoustic Waves ◽  
Young's Modulus ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Bovine Pericardium ◽  
Uniaxial Tensile ◽  
Non Invasive

BACKGROUND: Heart valves are exposed to a highly dynamic environment and underlie high tensile and shear forces during opening and closing. Therefore, analysis of mechanical performance of novel heart valve bioprostheses materials, like SULEEI-treated bovine pericardium, is essential and usually carried out by uniaxial tensile tests. Nevertheless, major drawbacks are the unidirectional strain, which does not reflect the in vivo condition and the deformation of the sample material. An alternative approach for measurement of biomechanical properties is offered by Brillouin confocal microscopy (BCM), a novel, non-invasive and three-dimensional method based on the interaction of light with acoustic waves. OBJECTIVE: BCM is a powerful tool to determine viscoelastic tissue properties and is, for the first time, applied to characterize novel biological graft materials, such as SULEEI-treated bovine pericardium. Therefore, the methods has to be validated as a non-invasive alternative to conventional uniaxial tensile tests. METHODS: Vibratome sections of SULEEI-treated bovine pericardium (decellularized, riboflavin/UV-cross-linked and low-energy electron irradiated) as well as native and GA-fixed controls (n = 3) were analyzed by BCM. In addition, uniaxial tensile tests were performed on equivalent tissue samples and Young’s modulus as well as length of toe region were analyzed from stress-strain diagrams. The structure of the extracellular matrix (ECM), especially collagen and elastin, was investigated by multiphoton microscopy (MPM). RESULTS: SULEEI-treated pericardium exhibited a significantly higher Brillouin shift and hence higher tissue stiffness in comparison to native and GA-fixed controls (native: 5.6±0.2 GHz; GA: 5.5±0.1 GHz; SULEEI: 6.3±0.1 GHz; n = 3, p <  0.0001). Similarly, a significantly higher Young’s modulus was detected in SULEEI-treated pericardia in comparison to native tissue (native: 30.0±10.4 MPa; GA: 31.8±10.7 MPa; SULEEI: 42.1±7.0 MPa; n = 3, p = 0.027). Native pericardia showed wavy and non-directional collagen fibers as well as thin, linear elastin fibers generating a loose matrix. The fibers of GA-fixed and SULEEI-treated pericardium were aligned in one direction, whereat the SULEEI-sample exhibited a much denser matrix. CONCLUSION: BCM is an innovative and non-invasive method to analyze elastic properties of novel pericardial graft materials with special mechanical requirements, like heart valve bioprostheses.

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.

Mechanical Characterization of Porcine Skin Starting Material

2021 ◽  
Author(s):  
Bin Zhang ◽  
Shawn Chester ◽  
Siva Nadimpalli ◽  
Justin Suriano ◽  
David Theis ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Medical Devices ◽  
Tensile Tests ◽  
Starting Material ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Porcine Skin ◽  
Curve Fit ◽  
Tensile Curve ◽  
Industrial Standards

Abstract Porcine skin has been used as a starting material in several released mesh medical devices. Although this controlled animal derived material is prevalent in tissue engineered medical devices, little is known about its mechanical properties. This study mechanically characterized Porcine Skin Starting Material (PSSM), provided by Midwest Research Swine. Uniaxial tensile tests were performed on samples cut from different regions (back and neck) and orientations (parallel and perpendicular to the spine) on the PSSM. The stress-stretch relationship was determined for each sample utilizing a load frame equipped with a Digital Image Correlation measurement system. The PSSM skin demonstrates the classic nonlinear and linear regions seen in other biologic tissues. A bilinear curve fit method was used to separate the nonlinear and linear regions of the tensile curve, and each region was analyzed with an Ogden and linear model respectively. The results show that the tensile curve is better described with this method as opposed to analyzing the full curve with one model. A comparison was made between samples cut from the different regions and orientations. There were significant differences between the failure measures and mechanical indices from the two regions, and on average the back behaved anisotropically and the neck isotropically. The PSSM mechanical properties from this study could serve as a preliminary guide for those exploring devices or processes in the tissue engineering field. The methods demonstrated in this study could also help characterize other biologic materials, and be used towards the development of tissue specific industrial standards.

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