residual strains
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2022 ◽  
Author(s):  
Abdelrahman Essa ◽  
Buddhika Abeyrathna ◽  
Bernard Rolfe ◽  
Matthias Weiss

Abstract Flexible Roll Forming (FRF) allows the forming of components with a variable cross-section along the length of the component. However, the process has only limited application in the automotive industry due to wrinkling in the flange which currently prevents the forming of high strength steels and limits the part shape complexity. This paper presents a new forming technology, Incremental Shape Rolling (ISR), where a pre-cut blank is clamped between two dies and then a single forming roll is used to incrementally form the material to the desired shape. The new process is similar to some Incremental Sheet Forming (ISF) approaches but with the difference that Incremental Shape Rolling (ISR) allows the manufacture of longitudinal components from high strength metal sheets. In this work, a numerical model of the ISR of a straight section is developed. Experimental prototyping trials are performed and are used to validate the numerical model which is then applied to analyse the new forming process. The results show that in ISR, tensile residual strains are developed in the flange. Flange wrinkling is observed and directly linked to the number of forming passes that are used in the process.


Author(s):  
Gilles Dusfour ◽  
Dominique Ambard ◽  
Patrick Cañadas ◽  
Simon Lefloch

Up-to-date, back pain is among the most prevalent health issues and generally takes its origins from lesions of the annulus fibrosus (AF). While the AF ex vivo mechanical properties are increasingly well understood, in vivo data are still missing. In particular, very few studies have precisely measured the residual strains within the AF and thus the in vivo deformation state of the AF is still miss-interpreted and miss-evaluated. In this work, we propose an original and robust method for the AF residual strains quantification via digital image correlation technics. Ten pig annulus fibrosus were extracted from adjacent vertebrae followed by a radial incision to release the residual strains. The operations were filmed and then analyzed by a custom digital image correlation software in order to quantify the circumferential, radial and shear residual deformations. Our results show that residual strains are of the same order of magnitude than the in vivo one. The average circumferential strains are in tension on the outer periphery ([3.32; 5.94]%) and in compression on the inner periphery ([−6.4; −1.69]%). The mean radial residual strains are essentially in compression ([−10.4; 2.29]%). Locally, radial and circumferential residual strains can reach really large values up to 40% of compression. The mean shear strains remain very small (−0.04% ± 2.88%). This study also shows that circumferential and radial residual strains evolve linearly along the radius and non-linearly along the angle. We propose a simple model to predict their spatial variations. Our results and methods will allow the quantification of more realistic in vivo strains and stresses within the human intervertebral disc.


2021 ◽  
Vol 6 ◽  
pp. 55-65
Author(s):  
Kamila Storchak ◽  
◽  
Nina Yakovenko ◽  
Olga Polonevych ◽  
Irina Sribna ◽  
...  

The laser irradiation of metallic surfaces by intense heat sources is used for the generation of short probing pulses, which propagate into thin specimens and enable one to estimate their structure and mechanical properties within the framework of the classical acoustic approach. High thermal stresses and residual strains occur during the short-term irradiation of the surface of a construction by an energy source of high density. In the present work, we solve the axially symmetric problem of a half-space under thermomechanical loading. We take into account the influence of volume and inelastic characteristics of separate phases on the residual stress-strain state of the half-space. The statement of the problem includes: Cauchy relations, equations of motion, heat conduction equation, initial conditions, thermal and mechanical boundary conditions. The thermomechanical behavior of an isotropic material is described by the Bodner-Partom unified model of flow. The problem is solved with using the finite element technique. The numerical realization of our problem is performed with the help of step-by-step time integration. The equations of motion are integrated by the Newmark method. The residual stress-strain state is described using the method of numerical solution of the axisymmetric dynamic problem for a half-space under thermomechanical loading and the flow model. We established that microstructural transformations, which are taken into account due to the thermophase volume strain and dependence of inelastic characteristics of the material on the phase composition, significantly reduce residual inelastic strain and promote the appearance of compressive stresses. The three-zone region of residual stresses field formation is obtained.


Sensors ◽  
2021 ◽  
Vol 21 (20) ◽  
pp. 6879
Author(s):  
Shaoquan Wang ◽  
Erik Sæter ◽  
Kaspar Lasn

Structural health monitoring (SHM) is a challenge for many industries. Over the last decade, novel strain monitoring methods using optical fibers have been implemented for SHM in aerospace, energy storage, marine, and civil engineering structures. However, the practical attachment of optical fibers (OFs) to the component is still problematic. While monitoring, the amount of substrate strain lost by the OF attachment is often unclear, and difficult to predict under long-term loads. This investigation clarifies how different attachment methods perform under time-dependent loading. Optical fibers are attached on metal, thermoset composite, and thermoplastic substrates for distributed strain sensing. Strains along distributed optical fiber sensors (DOFS) are measured by optical backscatter reflectometry (OBR) and compared to contact extensometer strains under tensile creep loading. The quality of the bondline and its influence on the strain transfer is analyzed. Residual strains and strain fluctuations along the sensor fiber are correlated to the fiber attachment method. Results show that a machine-controlled attachment process (such as in situ 3-D printing) holds great promise for the future as it achieves a highly uniform bondline and provides accurate strain measurements.


Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6007
Author(s):  
Hydayatullah Bayat ◽  
Andrzej Ubysz ◽  
Marek Maj ◽  
Marek Chalecki ◽  
Jarosław Wójt ◽  
...  

In the mechanics of concrete constructions, one distinguishes between residual and elastic strains. Cyclic loadings evoke changes mainly in the elastic strains; however, the total strains are decided by the sum of the residual and elastic strains. The knowledge of the ratio between the residual and total strains allows to predict the total deformations of a construction assuming it is made from an ideally elastic material. This paper presents the effect of the load level at the values of the residual strains for beams made of high-strength concretes and subjected to bending. The investigations showed that the share of residual strains for these concretes differed from the share of residual strains for concretes of lower classes. The investigations were made for cyclically loaded concrete samples and ferroconcrete beams for various relative load levels. The ratio between the residual and total strains was presented in the form of a dependence on the relative load level of the element. An important conclusion was that, after the crack formation, the share of residual stresses reduced, along with the increase in the concrete strength and elastic features of the construction which started to predominate.


Author(s):  
Yi Chen ◽  
Lloyd V. Smith

AbstractIn this study, we consider the nonlinear viscoelastic–viscoplastic behavior of adhesive films in scarf joints. We develop a three-dimensional nonlinear model, which combines a nonlinear viscoelastic model with a viscoplastic model using the von Mises yield criterion and nonlinear kinematic hardening. We implement an iterative scheme for the viscoplastic solution and a numerical algorithm with stress correction for the combined viscoelastic–viscoplastic model into finite element analysis. The viscoelastic component of the model is calibrated using creep-recovery data from adhesive films in scarf joints. The viscoplastic parameters are calibrated from the residual strains of recovered creep tests with varying load durations. A two-dimensional form of the model shows good agreement with the three-dimensional model for the scarf joint considered in this work and is compared with experiment. The numerical results show favorable agreement with the experimental creep and recovery responses of two epoxy adhesive systems. We also discuss the contribution of nonlinear viscoelasticity and viscoplasticity to the stress/strain distribution along the adhesive center lines. Viscoplasticity tends to lower the stress concentration.


2021 ◽  
Author(s):  
Waqas Badar ◽  
Husna Ali ◽  
Olivia N Brooker ◽  
E. Newham ◽  
Tim Snow ◽  
...  

AbstractThe bone-cartilage interface (BCI) and underlying calcified plate is a universal feature in diarthrodial joints. The BCI is an important mechanically-graded interface subjected to shear and compressive strains, and changes at the BCI have been linked to osteoarthritis progression. Here we report the existence of a physiological internal strain gradient (pre-strain) across the BCI at the ultrastructural scale of the extracellular matrix constituents, specifically the collagen fibril. We use X-ray scattering that probes changes in the axial periodicity of fibril-level D-stagger of tropocollagen molecules in the matrix fibrils, as a measure of microscopic pre-strain. We find that mineralized collagen nanofibrils in the calcified BCI are in tension pre-strain relative to the underlying trabecular bone. This behaviour contrasts with the previously accepted notion that fibrillar pre-strain (or D-stagger) in collagenous tissues always reduces with mineralization due to reduced hydration and associated swelling pressure. Within the calcified tissue, a finer-scale gradient in pre-strain over ~50μm is likely linked to the tidemark. The increased fibrillar pre-strain at the BCI is linked to prior research reporting large tissue-level residual strains under compression. The findings may have biomechanical adaptative significance: higher in-built molecular level resilience/damage resistance to physiological compression, and the disruption of the molecular-level pre-strains during remodelling of the BCI may be a potential factor in osteoarthritis-based degeneration.


2021 ◽  
Vol 2021 ◽  
pp. 1-5
Author(s):  
Lin Fang ◽  
Quan Yuan ◽  
Bin Wu ◽  
Honglin Li ◽  
Mengyang Huang

Surface elasticity and residual stress have a strong influence on the effective properties of nanowire (NW) due to its excessively large surface area-to-volume ratio. Here, the classical displacement method is used to solve the field equations of the core-surface layer model subjected to tension and torsion. The effective Young’s modulus is defined as the ratio of normal stress to axial strain, which decreases with the increase in NW radius and gradually reaches the bulk value. The positive or negative surface residual stresses will increase or decrease Young’s modulus and shear modulus due to the surface residual strains. Nonzero radial and circumferential strains enhance the influence of surface moduli on the effective modulus.


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