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Understanding By Design

The protective character of oxide scales developed at high temperature on metallic alloys strongly depends on the adherence of the scales which must be related to the stress level in the scales. Thus, after a review of the origins of the stresses in such scales, the methods actually used for determining the stresses either at room temperature or during the oxidation sequences are briefly mentioned. Results concerning NiO, Cr 2 O 3 and Al 2 O 3 scales are presented. These results are discussed in relation with the stress origin and they are compared with results obtained by theoretical modelling. It is suggested that growth stresses are particularly related to the scale growth mechanism, and that they are of minor importance compared with thermal stresses so that, for the systems considered, the adherence loss mainly results from the thermal stresses and/or from the poor quality of the scale-metallic substrate interface due to the defect concentration at this interface.

Stresses in NiO, Cr2O3 and Al2O3 oxide scales

Life prediction of coated and uncoated metallic interconnect for solid oxide fuel cell applications

Mechanical failure of thin brittle coatings

Simple mechanical models which could be used to calculate the stresses in an oxide scale on a flat metal substrate are presented. The sources for these stresses and the experimental techniques for measuring stresses and oxide failure are also briefly summarized. The options for stress relief in oxide scales are listed. The importance of lateral oxide growth and oxide plasticity is emphasized. Both processes result in stress relief without scale failure. This is followed by a detailed survey of the proposed mechanisms and models for oxide scale failure under tensile or compressive forces. Experimental evidence in support of these mechanisms is examined and the critical factors for predicting oxide failure are given.

The mechanical failure of oxide scales under tensile or compressive load

When an oxidized metal is cooled from a high temperature, stresses are produced at the metal-scale interface, owing to the difference in thermal expansion rates of the oxide and metal. Such stresses become time- and temperature-dependent if the scale or underlying metal creeps as cooling occurs. A model is presented which describes thermally induced stresses in the scale and accounts for partial stress relaxation by creep of the metal substrate and/ or the scale. The expected stresses are a function of the material parameters: thermal expansion coefficients, elastic modulii, and creep rates of both metal and scale. To illustrate a range of behaviors, we have presented example calculations for three Cr2O3 forming metals, Ni-30Cr, pure Cr, and MA-754. The effect of stress relaxation during thermal cycling was also examined briefly. In these examples, creep of the Cr2O3 scale was not expected to be important.

A Model for stress generation and relief in oxide — Metal systems during a temperature change

STATEMENT The healthcare simulation (HCS) community recognizes the importance of quality management because many novel simulation devices and techniques include some sort of description of how they tested and assured their simulation's quality. Verification and validation play a key role in quality management; however, literature published on HCS has many different interpretations of what these terms mean and how to accomplish them. The varied use of these terms leads to varied interpretations of how verification process is different from validation process. We set out to explore the concepts of verification and validation in this article by reviewing current psychometric science description of the concepts and exploring how other communities relevant to HCS, such as medical device manufacturing, aviation simulation, and the fields of software and engineering, which are building blocks of technology-enhanced HCS, use the terms, with the focus of trying to clarify the process of verification. We also review current literature available on verification, as compared with validation in HCS and, finally, offer a working definition and concept for each of these terms with hopes to facilitate improved communication within, and with colleagues outside, the HCS community.

Exploring Validation and Verification: How they Different and What They Mean to Healthcare Simulation

INTRODUCTION Several different whole-body physiology simulation tools (PST) using modeling techniques are now available with potential use for healthcare simulation, but these novel technologies lack objective analysis from an independent organization. METHODS We identified BioGears, HumMod, and Muse as 3 PSTs that met our requirements for testing. We ran mild, moderate, and severe hemorrhage scenarios on each PST and collected outputs for comparison with each other and published human physiology data. RESULTS All PSTs tested followed the expected tachycardic and hypotensive response to hemorrhage for all levels of severity with variable qualitative patterns. Complete data for analysis were not available in all PSTs for urine output, stroke volume, blood volume, hemoglobin, and serum epinephrine concentration, but the partial findings are discussed in detail. We determined the predicted time to reach hemorrhage shock based on the hemorrhage guidelines and compared this with time to cardiovascular collapse from each PST. Overall, the differences from known human physiology were much larger than expected before testing and trends show HumMod with the smallest difference for severe (-6.25%) and moderate (-1.42%) and Muse with the smallest difference for mild hemorrhage (27.9%). BioGears demonstrated the largest differences in all classifications of severity. CONCLUSIONS Our analysis of currently available whole-body PSTs provides insight into the novel, evolving field. We hope our efforts shed light to a wider audience to the exciting developments and uses of mathematical modeling for whole-body simulation and the potential for integration into healthcare simulation for medical education.

Comparing Hemorrhage in Human Physiology Simulation Tools: How They Compare With Expected Human Physiology and Each Other.

PurposeCompare outcomes in CF-FML LVAD patients who received a CHI after implantation until they reached a therapeutic INR on warfarin to patients who were started on warfarin only and did not receive a CHI.MethodsA retrospective analysis using chart review and the institutional LVAD database was completed on 27 patients.Results5 of the 27 patients did not receive a CHI after implantation of CF-FML LVAD (due to a medication shortage), they were started on warfarin post-operative day 1 or 2 (POD1 or POD2) for an INR goal of 2-3. CHI was initiated on the remaining patients (DOS-POD8) and PTT reached therapeutic range POD2 (DOS-POD9). 2 patients did not reach therapeutic PTT before their INR was therapeutic. The CHI patients were started on warfarin POD4 (DOS-POD14). INR was therapeutic for patients without CHI POD6 (POD5-POD11). INR was therapeutic for patients with CHI POD10 (POD2-POD31). The no CHI patients reached therapeutic INR faster and were discharged from index hospitalization sooner. The no CHI patients had similar or less adverse events (AEs) then the CHI patients (Image 1).ConclusionIn a small cohort of patients, initiation of warfarin anticoagulation without CHI was not associated with thromboembolic complications. Further work to identify populations of LVAD supported patients who need less anticoagulation post-operatively is warranted before considering practice changes. Compare outcomes in CF-FML LVAD patients who received a CHI after implantation until they reached a therapeutic INR on warfarin to patients who were started on warfarin only and did not receive a CHI. A retrospective analysis using chart review and the institutional LVAD database was completed on 27 patients. 5 of the 27 patients did not receive a CHI after implantation of CF-FML LVAD (due to a medication shortage), they were started on warfarin post-operative day 1 or 2 (POD1 or POD2) for an INR goal of 2-3. CHI was initiated on the remaining patients (DOS-POD8) and PTT reached therapeutic range POD2 (DOS-POD9). 2 patients did not reach therapeutic PTT before their INR was therapeutic. The CHI patients were started on warfarin POD4 (DOS-POD14). INR was therapeutic for patients without CHI POD6 (POD5-POD11). INR was therapeutic for patients with CHI POD10 (POD2-POD31). The no CHI patients reached therapeutic INR faster and were discharged from index hospitalization sooner. The no CHI patients had similar or less adverse events (AEs) then the CHI patients (Image 1). In a small cohort of patients, initiation of warfarin anticoagulation without CHI was not associated with thromboembolic complications. Further work to identify populations of LVAD supported patients who need less anticoagulation post-operatively is warranted before considering practice changes. 

Outcomes in Patients with a Centrifugal Flow with Full Magnetic Levitation Left Ventricular Assist Device (CF-FML LVAD) Who Did Not Receive Bridging with a Continuous Heparin Infusion (CHI) After Implantation

John Jacob Barnes

Papers

A Model for stress generation and relief in oxide — Metal systems during a temperature change

Exploring Validation and Verification: How they Different and What They Mean to Healthcare Simulation

Comparing Hemorrhage in Human Physiology Simulation Tools: How They Compare With Expected Human Physiology and Each Other.

Outcomes in Patients with a Centrifugal Flow with Full Magnetic Levitation Left Ventricular Assist Device (CF-FML LVAD) Who Did Not Receive Bridging with a Continuous Heparin Infusion (CHI) After Implantation