Elastic-plastic defect interaction in (a)symmetrical double edge notched tension specimens

Interaction of defects tends to intensify their crack driving force response compared to the situation where these defects act independently. The interaction between multiple defects is addressed in engineering critical assessment standards like BS7910 and ASME B&PV Section XI. Nonetheless, the accuracy of these rules is open to debate since all of them are based on re-characterization procedures which in essence introduce conservativeness. The authors have developed a fully parametric finite element (FE) model able to generate multiple notches in different topologies, in order to investigate their interaction effect. An experimental validation study is conducted to verify the FE model in terms of CTOD response and surface strain distribution. To that end, symmetrically and asymmetrically double edge notched tension specimens are tensile tested and their deformation monitored by means of 3D digital image correlation. In this study the CTOD is opted as a local criterion to evaluate the interaction between notches. These results are compared with an evaluation of strain patterns on a specimen’s surface, as a global interaction evaluation. Through this comparison a deeper understanding is gained to allow us to develop a novel approach to address flaw interaction. Moreover, the validation of the FE model allows future studies of interaction between other defect types (e.g., semi-elliptical, surface breaking) in plate-like geometries

Pulsed eddy current applied to measure residual stress in welding

Welding is a manufacturing process of joining components that is dominant in industries that include civil, oil and gas, automotive, etc. Although it has various benefits, welding still causes residual stresses to remain in a component after welding. Residual stresses may result in unexpected failure and may worsen mechanical performance. Common methods to measure residual stresses include hole-drilling and X-ray diffraction and are characterized by their lack of reliability and complicated implementation process. In this study, pulsed eddy current (PEC) is introduced as a promising technique to measure subsurface residual stress in welding. First, the PEC method is calibrated and the correlation between signals and known stresses are identified, and then the residual stress in a welded component is estimated, and finally, the residual stresses measured by PEC were compared to the results obtained by the finite element technique

Immunomodulatory properties of mesenchymal stem cells: Cytokines and factors

Mesenchymal stem cells (MSCs) are defined as undifferentiated cells that are capable of self renewal and differentiation into several cell types such as chondrocyte, adipocyte, osteocyte, myocyte, hepatocyte, and neuron-like cells. MSC can be isolated from bone marrow, umbilical cord blood, adipose tissue, placenta, periosteum, trabecular bone, synovium, skeletal muscle, and deciduous teeth. Immunomodulatory of MSCs is one of the important issues nowadays, because this aspect can be clinically applied for graft-versus-host and autoimmune diseases. In this review, we tried to discuss in detail about cytokines and factors such as members of the transforming growth factor superfamily (transforming growth factor-β), hepatic growth factors (HGF), prostaglandin E2 (PGE2), IL-10, indolamine 2,3-dioxygenase (IDO), nitric oxide (NO), heme oxygenase-1 (HO-1), and human leukocyte antigen-G (HLA-G) that are involved in immunomodulatory of MSCs. © 2011 John Wiley & Sons A/S

A strain-based approach to study interaction between non-coplanar through-thickness edge notches

Structural integrity assessment procedures to assess the effect of interaction between multiple adjacent flaws normally consist of two stages. First, alignment rules categorize non-coplanar flaws as aligned or non-aligned. Second, combination rules classify aligned flaws as interacting or non-interacting. Although these criteria are applied to different failure modes like brittle fracture, elastic–plastic fracture and plastic collapse, most of them were developed based on linear elastic fracture mechanics for the sake of simplicity. However, there are very limited references available for the technical background of these criteria. This lack of justifying backgrounds becomes more critical when applying these procedures to any other failure modes other than brittle fracture. This article studies the interaction between non-coplanar edge notches in scenarios of large deformation. Hereto, strain patterns are studied through full-field deformation measurements utilizing both experimental and numerical tools. Digital image correlation is used to measure strain during experiments and to verify the finite element analyses. The results show that in addition to the crack driving force, which represents a local response of notches, the global strain distribution within the specimen in terms of strain patterns can be used to probe the interaction between non-coplanar flaws. The authors suggest a novel criterion based on the trajectory of maximum equivalent strain to distinguish between aligned and non-aligned flaws. This study is based on double-edge notched tension specimens and gives a fundamental insight into flaw interaction in failure modes other than brittle fracture. </jats:p

Using 3D Digital Image Correlation (3D-DIC) to measure CTOD in a semi-elliptical surface crack

The subsurface nature of Crack Tip Opening Displacement (CTOD) makes its direct measurement very difficult, if not impossible. During fracture toughness testing, CTOD is commonly calculated by applying a plastic hinge model using externally applied clip gauges. However, clip gauge CTOD calculations merely provide information relating to the center of the defect (which is typically the most critical point, but not always). For the case of a finite-length surface defect, CTOD will be variable over the defect front. Exact knowledge of CTOD over the entire front is useful for detailed calculations, such as crack profile evolution due to ductile tearing or calculations involving interacting defects. To experimentally measure the CTOD at locations other than the center of the crack, the authors propose a technique based on full field three-dimensional profile measurement of the notched surface by means of stereoscopic Digital Image Correlation (3D-DIC). The method is based on the plastic hinge model assuming that the crack flanks rotate in a rigid manner around a plastic hinge point in the un-cracked ligament. Having measured full-field out-of-plane displacement at the surface of the specimen around the crack using the 3D-DIC method, CTOD can be inferred over the entire crack front. Results show that, due to the acceptable agreement between the DIC based calculation and CTOD measured from cast replicas, the proposed technique has a sufficient accuracy to measure CTOD on the entire crack front in plastically deforming specimens

Finite element and experimental investigation on the effects of temperature, strain and strain rate on microstructure and mechanical properties of FSSWed TRIP steel joints

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Effects of two different hip-knee-ankle-foot orthoses on postural stability in subjects with spinal cord injury : a pilot study

Purpose Evaluation of two different hip-knee-ankle-foot orthoses (HKAFOs; medial linkage reciprocating gait orthosis [MLRGO] and isocentric reciprocating gait orthosis [IRGO]) using gait and postural stability analysis in four subjects with spinal cord injury (SCI). Overview of Literature To the best of our knowledge, no study has evaluated postural stability in subjects with SCI when using MLRGO and IRGO. Methods The relative efficacy of each orthosis was evaluated with relevant gait parameters, and an assessment of postural stability and sway during usage was made. Each analysis was conducted following an appropriate period of training and acclimatization. The gait parameters employed in the study were walking speed, cadence, and endurance; these were recorded and analyzed using current, validated methods. Postural stability was assessed using a verified force plate measurement system, and a modified Falls Efficacy Scale (mFES) was used for the measurement of postural sway and the perceived fear of falling. Results Walking speed, cadence, and endurance increased with the use of both HKAFOs. When the two types of HKAFOs were compared, all the parameters showed a slight (but not significant) increase with the use of MLRGO compared with the use of IRGO. In contrast, there were slight but insignificant improvements in postural sway with the use of IRGO. However, although there were no significant differences between the two sets of mFES scores, there was a slightly reduced fear of falling with the use of MLRGO compared with the use of IRGO in the static standing position. Conclusions It is noteworthy that meaningful interpretations of results can only be drawn if a larger sample is employed. This pilot study showed no significant data; however, the results indicate that the use of MLRGO is superior to that of IRGO in terms of potential improvement in the mobility and confidence levels of subjects with SCI

COSC 101

An introduction to computer science through the study of programming utilizing the programming language Python. Topics include program control, modular design, recursion, fundamental data structures including lists and maps, and a variety of problem-solving techniques