Study of fatigue crack growth in 6063-T6 aluminum alloy

The present study relates to fracture mechanics and its aim is to validate the experimental analysis with analytical analysis and find out a relationship between loading parameters and crack growth rate for 6063-T6 Aluminum Alloy. All analysis was done on Side edge notch specimen. The constant U was found to depend on stress ratio R. Variation in load range affects the crack growth rate constant m. For constant load range its variation was negligible, constant C was almost constant at variable load range. Variation of maximum load affects constant C

Effect of strain hardening on fatigue crack closure in aluminum alloy under constant amplitude with single overload

In this study effect of strain hardening on crack closure has been examined with the help of experiments and finite element method on the side edge notched specimen of five different Aluminum alloy (3003 Al, 5052 Al, 6061 T6, 6063 T6, 6351) in mode I under constant amplitude fatigue loading with single overload using Abaqus® 6.10 which is very well accepted FEM application in research. Extended Finite Element Method Module has been used to determine effective stress intensity factor at the crack tip while propagation takes place. FEM results have given good agreement with experimental results. Regression analysis has also been done with SPSS® 16 and dependency of strain hardening coefficient on crack closure has analyzed. A generalized empirical formula has been developed based on strain hardening to calculate effective stress intensity range ratio and a modified Paris law has also been formulated for these aluminum alloy

Modeling of an active suspension system with different suspension parameters for full vehicle

55-63An active suspension system attempts to overcome these compromises so as to provide the best performance for controlling the vehicle. A fully active suspension system aims to control the suspension over the full bandwidth, increase load carrying capacity, handling and ride quality. A model for vehicle’s dynamics while using an active suspension system has been developed. The equations are cast in both the state space form and transfer function forms. To compare the ideal system and a real system, a comparative analysis is also performed by incorporating various sensing and actuation constraints such as time delay and discrete sampling. Simple PID as well as feed-forward controllers is designed and the response is simulated for various disturbances such as road excitations and those arising due to cornering. Parameter studies are also performed to assess the response to various suspension properties. The comparison of the active suspension with respect to the passive suspension indicates significant improvement in performance characteristics such as riding comfort, tendency to rollover and road traction. The studies on the effect of sensing and actuation constraints provide valuable insights into the use of low-cost and/or robust control system elements

Modeling of an active suspension system with different suspension parameters for full vehicle

An active suspension system attempts to overcome these compromises so as to provide the best performance for controlling the vehicle. A fully active suspension system aims to control the suspension over the full bandwidth, increase load carrying capacity, handling and ride quality. A model for vehicle’s dynamics while using an active suspension system has been developed. The equations are cast in both the state space form and transfer function forms. To compare the ideal system and a real system, a comparative analysis is also performed by incorporating various sensing and actuation constraints such as time delay and discrete sampling. Simple PID as well as feed-forward controllers is designed and the response is simulated for various disturbances such as road excitations and those arising due to cornering. Parameter studies are also performed to assess the response to various suspension properties. The comparison of the active suspension with respect to the passive suspension indicates significant improvement in performance characteristics such as riding comfort, tendency to rollover and road traction. The studies on the effect of sensing and actuation constraints provide valuable insights into the use of low-cost and/or robust control system elements. Full vehicle model, State space equation, Passive and active suspension system, PID controller, Road profile, MATLAB and SIMULIN

Intergranular Corrosion of Deformed SS304

Intergranuular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC) of commercial stainless steels e.g. type 304 and 316 are frequently observed in several process environments. These localized attacks are normally attributed to the carbide precipitation and concomitant depletion of chromium near grain boundary due to alloy exposure to sensitization temperature. Such undesirable microchemistry is expected to be changed further if the material undergoes deformation prior to sensitization

Effects of Cold Deformation Prior to Sensitization on Intergranular Stress Corrosion Cracking of Stainless Steel

The effects of deformation, prior to sensitization, on intergranular stress corrosion cracking (IGSCC) were studied on the AISI 304 (UNS S30400) stainless steel (SS). The degree of sensitization (DOS) was quantified by the double loop electrochemical potentiokinetic reactivation (DL-EPR) method. The susceptibility to IGSCC was investigated by the slow strain rate test (SSRT) carried out in polythionic acid (PTA) solutions. The results were complemented by scanning electron microscopy (SEM) fractographs. Deformation was found to accelerate sensitization, and a peak in sensitization vs. deformation was always observed. This peak was found to shift toward lower deformations with an increase in sensitization temperature. At 700°C, prior deformation is able to desensitize or heal the SS after 24 h. IGSCC was observed in AISI 304 SS after some treatments. No one-to-one correspondence was observed between IGSCC and DOS; this could be explained by the fact that the DOS measured by the DL-EPR indicates the depleted regions below ~15% Cr, whereas IGSCC depends on the availability of continuous grain boundary paths that are chromium-depleted, along with strain rate and environment (pH, temperature, etc.). Deformation prior to sensitization causes carbide formation and chromium depletion to occur near dislocations within the grain interiors, in addition to along grain boundaries. The DOS does not differentiate between these interior regions and the grain boundary regions, and shows Sensitization is a common phenomenon in stainless steels (SS) when they are exposed to temperatures ranging from about 400°C to 800°C.1-20 Classical sensitization results from the nucleation and growth of chromium carbide along grain boundaries (in solution-annealed SS and nickel alloys) with simultaneous depletion of chromium in adjacent grain boundary regions. The extent of chromium depletion in near grain boundary regions is limited by the equilibrium concentration of chromium at the carbide-matrix interface. The equilibrium chromium level depends on the temperature, the chromium activity coefficient, the carbon activity, and the equilibrium constant for carbide formation. Hall and Briant showed the equilibrium chromium concentrations to be 6.6, 8.4, and 10.8 wt% in AISI 316LN(1) (UNS S31603)(2) sensitized at 600, 650, and 700°C, respectively.21 Sensitization occurs in the temperature range where carbide is thermodynamically stable (500°C)

Fluid Structure Interaction Study of Stenosed Carotid Artery Considering the Effects of Blood Pressure and Altered Gravity

Atherosclerosis is a very common cardiovascular disease (CVD) causing increased morbidity. Atherosclerosis is a disease that involves several factors and usually affects the wall of the arterial bifurcations. Advanced Computational Fluid Dynamics (CFD) techniques has the potential to shed more light in understanding of the causes of atherosclerosis and perhaps in its early diagnosis. Fluid Structure Interaction (FSI) study was carried out on two different three dimensional patient specific cases (a) Normal carotid bifurcation and (b) Stenosed carotid bifurcation. Physiological conditions were considered to evaluate hemodynamic parameters and understand the origin and progression of atherosclerosis in the carotid artery bifurcation, first for the normal and then with hypertension disease. Commercial software ANSYS and ANSYS CFX (version 19.0) was used to perform a two-way FSI using a fully implicit second-order backward Euler differencing scheme. Arterial response was calculated by employing an Arbitrary Lagrangian–Eulerian (ALE) formulation and using the temporal blood response. The carotid artery bifurcation caused a velocity reduction and backflow was observed causing a reduction in the shear stress. A low shear stress resulted due to an oscillatory behavior at the start point of the internal carotid artery near the carotid sinus. Shear stresses are obtained by using anatomically realistic 3D geometry and representative physiological conditions. Results of this study agree with those in the literature showing that the regions with low wall shear stress. Geometry and flow conditions greatly affected the hemodynamics of the carotid artery. Furthermore, regions of relatively low wall shear stress were observed post stenosis, which is a known cause of plaque development and progression. Under altered gravity conditions the same artery was studied to determine the flow conditions and predict the progression of plague

Neoadjuvant chemotherapy or chemoradiotherapy in head and neck cancer

The multidisciplinary approach to treating squamous cell carcinoma of the head and neck is complex and evolving. Chemotherapy is increasingly being incorporated into the treatment of squamous cell carcinoma of the head and neck. Previously, radiotherapy following surgery was the standard approach to the treatment of loco regionally advanced resectable disease. Data from randomized trials have confirmed the benefits of concurrent chemo radiotherapy in the adjuvant setting. Chemo radiotherapy is also the recommended approach for unresectable disease. Advanced loco regional disease is the most frequent clinical situation in Head and Neck cancer. The standard of care for most clinicians is a multidisciplinary treatment with concomitant chemotherapy plus radiotherapy (CRT). However, retrospective studies have shown that in patients treated with CRT there was a relative increase in systemic relapse due to a lack of systemic control. For this reason a renewed interest has appeared for the incorporation of induction chemotherapy in the treatment of locally advanced Head and Neck Cancer. Furthermore new combination regimens with taxanes have shown to be more active than the classical cisplatin and 5-fluorouracil induction regimen. Novel targeted agents, such as epidermal growth factor receptor antagonists, are showing promise in the treatment of patients with both loco regionally advanced and recurrent/metastatic squamous cell carcinoma of the head and neck

The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel

The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability