Prediction of viscoelastic and plastic properties of polymers using indentation

Indentation methodologies are gaining popularity as they provide means of local property estimation, utilize smaller sample sizes, and do not destroy specimens. Classically, indentation has been used to measure hardness and Young’s modulus [1], but researchers have also proposed ways of predicting stress–strain curves [2], yield strength [3], and fracture toughness [3]. Different indentation techniques are being used by researchers for different types of investigations. Nanoindentation is an indentation at very small scales to obtain local properties via single indent. Reference Point Indentation (RPI) is a technique wherein multiple indents are carried out at the same location and the material response with repeated loading is monitored. Researchers have shown that increase in indentation depth during loading cycles can be used to predict material’s resistance to fracture [4]. Osteoprobe is a hand held indentation device which has been designed for in-situ bone quality measurements in clinical setting. In this study, we investigate the viscoelastic and plastic properties of polymers like PMMA using different microindentation techniques. Nine different polymers have been selected, which are commonly used for rapid prototyping applications. Some of the polymers exhibit very rubber like behavior, whereas others are stiffer and brittle. Indentation experiments are conducted on the nine polymers using the RPI equipment as well as the Osteoprobe. Similarities and differences in material behavior and predicted properties between these methods are of particular interest. Computational models can help in predicting material properties where analysis of experimental data becomes intricate. Load-deformation curves from experiments can be matched with results of finite element simulations, helping us to evaluate material properties via an inverse problem. Different substrate materials call for different material models and constitutive laws to be used. Material models can range from very simple elastic isotropic models to very complex viscoplastic models coupled with damage laws. Given such plethora of material models, it is important to select the right material model that reflects mechanical behavior of the material of interest. Uniaxial compressive and tensile testing can give us an estimate of elastic and plastic properties of material, whereas stress relaxation tests give us an estimate of viscous response. Coupling these responses together in an appropriate constitutive law meaningfully is still a challenge. Gaining better understanding of parameters obtained from these indentation experiments will not only help the engineering community but will also assist in prediction of material properties of biological tissue like bone for disease diagnosis. REFERENCES [1] Hansma, P.K., Turner, P.J., Fantner, G.E. Bone diagnostic instrument. Rev. Sci. Instrum. 2006, 77, 075105. [2] Hansma, P., Turner, P., Drake, B., Yurtsev, E., Proctor, A., Mathews, P., Lulejian, J., Randall, C., Adams, J., Jungmann, R., Garza-de- Leon, F., Fantner, G., Mkrtchyan, H., Pontin, M., Weaver, A., Brown, M.B., Sahar, N., Rossello, R., Kohn, D. The bone diagnostic instrument II: Indentation distance increase. Rev. Sci. Instrum. 2008, 79, 064303. [3] Randall, C., Mathews, P., Yurtsev, E., Sahar, N., Kohn, D., Hansma, P. The bone diagnostic instrument III: Testing mouse femora. Rev .Sci. Instrum. 2009, 80, 065108. [4] Gallant, Maxime A., et al. Reference-point indentation correlates with bone toughness assessed using whole-bone traditional mechanical testing. Bone. 2013, 53.1, 301–305

Does the distress factor hypothesis explain the size and value effects in equity returns?

The distress factor hypothesis says that value stocks and small stocks are distressed and therefore higher returns on such stocks are merely a compensation for higher risk. I test this hypothesis using z-scores, a cleaner proxy for bankruptcy risk than other proxies used in the literature such as dividend reductions or omissions. I find that unconditionally, distressed stocks earn significantly lower returns than non-distressed stocks and much underperformance is uninfluenced by size and B/M factors. I also find that z-score, size and B/M effects are stronger in different months suggesting little common variation between the three factors. The results show that size and B/M effects are unrelated to bankruptcy risk on an unconditional basis. Of crucial importance is a consideration of the time varying behaviour of bankruptcy risk premia and I consider explicitly the impact of changes in GDP growth rate and the impact of stock market movements on the pricing of distressed firms. I find that risk of bankruptcy is a systematic risk with distressed stocks registering strong underperformance during ‘bad’ states of the world. As with unconditional analysis, the results show there is no link between distress factor and size and B/M effects. Size and B/M effects are stronger in non-distressed stocks. To ensure that the empirical results are robust across different methodologies, I significantly expand on the work of Dichev (1998) by employing two different portfolio formation methods and individual securities in my analysis. My main results on z-scores are robust though size and B/M effects are sensitive to alternative trading rules. I also test the Fama & French (1993) three-factor model for the UK and find that it is unable to explain returns on negative z-score portfolios. A four-factor model that includes a factor mimicking the z-score effect is better specified. The primary contribution of this study is the direct evidence it provides on the distress factor hypothesis of higher returns on value stocks and small stocks and the four-factor model for stock returns. This research has important implications both for extant asset pricing theories and for practitioners especially in evaluation of portfolio performance and computation of abnormal returns

The impact of regulations on compliance costs, risk-taking, and reporting quality of the EU banks

The paper examines how the Statutory Audit and Corporate Reporting Directives (SACORD) affect the compliance costs, risk taking and quality of financial reporting of the EU banks. Using a natural experiment, we find that post SACORD, both compliance costs and risk taking increase significantly. However, the implementation of additional regulations seems to be effective in terms of improved quality of financial reporting. When we analyse the impact by size, we find that smaller banks face disproportionately higher increase in compliance costs while larger banks seem to engage in greater risk taking

Market in Financial Instruments Directive (MiFID), stock price informativeness and liquidity

The paper examines the impact of MiFID on stock price informativeness and liquidity in 28 EU countries. We find that post-MiFID the stock prices reflect greater firm specific information and the market becomes more liquid. Consistent with the ‘Catch-up Hypothesis’ our evidence shows that the impact of MiFID in terms of price informativeness is greater for countries that have weaker quality of regulation. We find that regulation with enforcement improves market efficiency. Our results are robust with respect to the choice of price informativeness and liquidity proxies as well as the control sample

The impact of statutory audit and corporate reporting directives on compliance costs, risk-taking and reporting quality of the EU banks

The paper examines the effects of recently introduced Statutory Audit and Corporate Reporting Directives (SACORD) on compliance costs and risk taking of the EU banks. Using data of 80 EU banks and 71 non-EU banks for the period 2004 to 2013, we estimate the effects of SACORD regulation compliance costs, risk taking and quality of reporting. Our results show that the economic effects of SACORD on audit fees are approximately 19 to 33 percent higher relative to the non-EU banks. We also find robust evidence of significant increase in in total compliance costs. The findings are consistent with those reported in the previous literature mainly for the US banks that regulation increases compliance costs. Further, we find that post SACORD, there is a significant increase in risk-taking and a decline in reporting quality. Findings suggest that the SACORD regulation does not appear to have the desired effects of constraining risk-taking by banks

Computational modeling of indentation of materials

This thesis focusses on computational modeling of several different indentation problems involving the microindentation, nanoindentation and reference point indentation (RPI). The goal of this thesis is to develop better understanding of indentation processes in different materials utilizing numerical methods. Indentation has been used for a long time for characterizing hardness of materials. Nanoindentation is a technique where a micron scale indenter is forced into a material of interest while monitoring load and displacement. Indentation techniques can be used to measure elastic modulus, hardness and viscoelastic properties of materials. The RPI technique uses a reference probe which sits on the surface of substrate and defines datum for test probe. The test probe indents the substrate multiple times using a cyclic load and computes nine different RPI outputs. The RPI outputs are not completely understood and there is a need for more research. This thesis presents four different studies. The first study deals with experimental and numerical investigation of indentation on Cr(Mo)-NiAl eutectic alloy. More specifically, the depth dependent strain partitioning between the layers of NiAl layered structure was measured using X-Ray microdiffraction. Finite element simulations were conducted to evaluate thermal strains due to cooling. Results from this simulation were further utilized to model microindentation of the eutectic composite. Strain data from simulations were compared with experimental results confirming experimentally observed trends. The second study deals with simulation of RPI on bone. Bone was modeled as a material that exhibits elastic, plastic, viscous and continuum damage behaviors. The RPI process was simulated as a cyclic indentation process using a finite element package Abaqus®. Effects of changing material properties, indentation force and number of cycles on the RPI outputs were evaluated computationally and compared with experimental works of similar nature and good coherence was demonstrated. Third study presents a statistical approach to study the RPI outputs. Various mechanical tests (compression tests, stress relaxation test, tensile tests) were conducted on multiple 3D printed polymers and properties were obtained. These properties were analyzed against the RPI data of polymers in order to find correlations. The study is currently ongoing and data collected till date is presented in this thesis. Fourth study presents a fast and efficient way of characterizing viscoelastic properties of soft materials based on experimental nanoindentation data and viscoelastic indentation tool on Nanohub. PMMA (polymethyl methacrylate) was subjected to nanoindentation to obtain experimentally time-displacement data. This data along with experimental parameters (loading time, force and indenter radius) serve as inputs to the Nanohub viscoelastic simulation tool. This tool can provide 3 or 5 viscoelastic constants for materials, assuming a Standard Linear Solid model for solids. Numerical data from simulations was matched against experimental data for two different loading rates and good match was observed

Traumatic avulsion of female urethra: a case report

Traumatic female urethral avulsion in the absence of a pelvic fracture is an exceedingly rare entity. We report a case of 26 years old lady with crescentic tear of anterior urethra from pubic symphysis. Management consisted of primary urethral repair

Switching portal technique in anterior cruciate ligament reconstruction: use of an extra low and medial portal

Background: Long term success of ACL reconstruction depends on accurate surgical technique of anatomic tunnel placements and proper rehabilitation protocol followed, and for accurate tunnel positioning various arthroscopic landmark should be visible clear with the use of various portals.Methods: All 112 surgeries were performed by a single surgeon in King Georges Medical University, Lucknow Orthopedic department operation theatre during July 2016- December 2018. An extra low and medial portal is created and then portal were switched between anteromedial and low medial one.Results: With the use of this portal the average surgical time was observed to be 43 minutes and no malpositioning of tunnel was encountered.Conclusions: This switching portal technique provides an excellent view of the femoral tunnel plot and gives consistent results with minimum complications

Bankruptcy risk prediction and pricing : unravelling the negative distress risk premium

In sharp contrast to the basic risk-return assumption of theoretical finance, the empirical evidence shows that distressed firms underperform non-distressed firms (e.g. Dichev, 1998; Agarwal and Taffler, 2008b). Existing literature argues that a shareholder advantage effect (Garlappi and Yan, 2011), limits of arbitrage (Shleifer and Vishny, 1997) or gambling retail investor (Kumar, 2009) could drive the underperformance. Herein, I test these potential explanations and explore the drivers of distress risk. In order to do so, I require a clean measure of distress risk. Measures of distress risk have usually been accounting-based, market-based or hybrids using both information sources. I provide the first comprehensive study that employs a variety of performance tests on different prediction models. My tests are based on all UK non-financial firms listed in the Main market segment of the London Stock Exchange (LSE) between September 1985 and October 2010. It includes 22,217 observations with 2,428 unique firms of which 202 went bankrupt. I find that hybrid models clearly outperform the accounting-based z-score (Taffler, 1983) and the market-based model of Bharath and Shumway (2008) (BS). Hybrid models forecast bankruptcies more accurately and they subsume the bankruptcy related information of z-score and BS. While there is little to distinguish between the hybrids in forecasting accuracy, tests of differential misclassification costs show that the highest economic value is delivered by the most parsimonious hybrid model of Shumway (2001) (Shum). The forecasting accuracy between z-score and BS depends on the sample period while both carry complementary bankruptcy related information. My study provides confirmatory evidence on the puzzling negative distress risk premium. Moreover, my tests show that the distress risk premium is independent of the distress risk proxy (Shum, z-score or BS). Remarkably, z-score –the weakest bankruptcy prediction model - subsumes the return related information of Shum and BS in cross-sectional tests suggesting that it might not be distress risk per se that is priced. My results provide no evidence that the potential explanations in the existing literature are able to account for the distress puzzle. As such, I find no confirmation for the shareholder advantage effect. Although the characteristics of firms with high limits of arbitrage and gambling features are shared by distressed firms, tests provide no evidence for their pricing relevance or their impact on the distress risk premium. This is the first study that deconstructs the distress measures into their component parts to unravel the distress risk premium and shows that the profitability components of Shum and z-score drive the premium. The composite measure without the information carried by profitability is insignificant in the pricing tests. In time-series regressions, I show that the pricing information carried by a profitability factor is able to reduce the distress risk premium. Portfolio analysis identifies low distress risk-high profitability firms as the key driver of the mispricing. The distress anomaly is not driven by distress risk but by profitability. Another major contribution is the use of the three approaches to assess distress risk. Together with the full range of major performance measures, I provide the first comprehensive test of the competing approaches. This study has important implications for the future research agenda on both, how we measure distress risk and the pricing of distress risk.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Yield-Area Optimizations of Digital Circuits Using Non-dominated Sorting Genetic Algorithm (YOGA)

ABSTRACT With shrinking technology, the timing variation of a digital circuit is becoming the most important factor while designing a functionally reliable circuit. Gate sizing has emerged as one of the efficient way to subside the yield deterioration due to manufacturing variations. In the past single-objective optimization techniques have been used to optimize the timing variation whereas on the other hand multi-objective optimization techniques can provide a more promising approach to design the circuit. We propose a new algorithm called YOGA, based on multi-objective optimization technique called Non-dominated Sorting Genetic Algorithm (NSGA). YOGA optimizes a circuit in multi domains and provides the user with Pareto-optimal set of solutions which are distributed all over the optimal design spectrum, giving users the flexibility to choose the best fitting solution for their requirements. YOGA overcomes the disadvantages of traditional optimization techniques, while even providing solutions in very stringent bounds