Size Effect and Notch Size Effect in Metal Fatigue

It is a well known phenomenon that the constant amplitude fatigue limit of a large component is lower than the fatigue limit of a small specimen made of the same material. In notched components the opposite occurs: the fatigue limit defined as the maximum stress at the notch is higher than that achieved with smooth specimens. These two effects have been taken into account in most design handbooks with the help of experimental formulas or design curves. The basic idea of this study is that the size effect can mainly be explained by the statistical size effect. A component subjected to an alternating load can be assumed to form a sample of initiated cracks at the end of the crack initiation phase. The size of the sample depends on the size of the specimen in question. The main objective of this study is to develop a statistical model for the estimation of this kind of size effect. It was shown that the size of a sample of initiated cracks shall be based on the stressed surface area of the specimen. In case of varying stress distribution, an effective stress area must be calculated. It is based on the decreasing probability of equally sized initiated cracks at lower stress level. If the distribution function of the parent population of cracks is known, the distribution of the maximum crack size in a sample can be defined. This makes it possible to calculate an estimate of the largest expected crack in any sample size. The estimate of the fatigue limit can now be calculated with the help of the linear elastic fracture mechanics. In notched components another source of size effect has to be taken into account. If we think about two specimens which have similar shape, but the size is different, it can be seen that the stress gradient in the smaller specimen is steeper. If there is an initiated crack in both of them, the stress intensity factor at the crack in the larger specimen is higher. The second goal of this thesis is to create a calculation method for this factor which is called the geometric size effect. The proposed method for the calculation of the geometric size effect is also based on the use of the linear elastic fracture mechanics. It is possible to calculate an accurate value of the stress intensity factor in a non linear stress field using weight functions. The calculated stress intensity factor values at the initiated crack can be compared to the corresponding stress intensity factor due to constant stress. The notch size effect is calculated as the ratio of these stress intensity factors. The presented methods were tested against experimental results taken from three German doctoral works. Two candidates for the parent population of initiated cracks were found: the Weibull distribution and the log normal distribution. Both of them can be used successfully for the prediction of the statistical size effect for smooth specimens. In case of notched components the geometric size effect due to the stress gradient shall be combined with the statistical size effect. The proposed method gives good results as long as the notch in question is blunt enough. For very sharp notches, stress concentration factor about 5 or higher, the method does not give sufficient results. It was shown that the plastic portion of the strain becomes quite high at the root of this kind of notches. The use of the linear elastic fracture mechanics becomes therefore questionable.

Development of data sheets for statistical evaluation of fatigue data

To enable a mathematically and physically sound execution of the fatigue test and a correct interpretation of its results, statistical evaluation methods are used to assist in the analysis of fatigue testing data. The main objective of this work is to develop step-by-stepinstructions for statistical analysis of the laboratory fatigue data. The scopeof this project is to provide practical cases about answering the several questions raised in the treatment of test data with application of the methods and formulae in the document IIW-XIII-2138-06 (Best Practice Guide on the Statistical Analysis of Fatigue Data). Generally, the questions in the data sheets involve some aspects: estimation of necessary sample size, verification of the statistical equivalence of the collated sets of data, and determination of characteristic curves in different cases. The series of comprehensive examples which are given in this thesis serve as a demonstration of the various statistical methods to develop a sound procedure to create reliable calculation rules for the fatigue analysis.

Factors Related to Study Success at Lappeenranta University of Technology

Tutkimuksen avulla selvitettiin opintomenestykseen liittyviä tekijöitä Lappeenrannan teknillisessä korkeakoulussa (LTKK). Tutkimus liittyi opetuksen ja oppimisen kehitystyöhön tuotantotalouden osastolla. Tutkimuksen viitekehyksen muodosti oppimistuloksia selittävä malli, joka on laadittu Tynjälän (1999) kokoaman mallin perusteella. Tutkimuksen perusjoukko muodostui LTKK:n läsnä olevista perusopiskelijoista lukuun ottamatta jatko- ja vaihto-opiskelijoita. Opiskelijat jaettiin ositetulla otannalla ryhmiin, joissa suoritettiin yksinkertainen satunnaisotanta. Otoskoko oli 645 opiskelijaa. Tiedonkeruumenetelmänä oli Internet-kysely. Aineisto analysoitiin useiden kvantitatiivisten ja kvalitatiivisten menetelmien avulla. Tutkimuksen tuloksia voidaan pitää luotettavina ja tutkimuksen avulla saatiin tärkeää ja hyödyllistä tietoa opintomenestyksestä ja oppimisprosesseista. Tulosten perusteella merkittävimmät oppimistuloksiin positiivisesti liittyvät tekijät ovat syväsuuntautunut opiskelustrategia ja luottaminen omiin kykyihin, ja negatiiviset tekijät ovat oppimisen itsesäätelyn puute, omien kykyjen epäily ja pintasuuntautunut opiskelustrategia. Merkitysorientoituneet, itsesäätelykykyiset opiskelijat menestyivät LTKK:ssa parhaiten.

Finnish buyers’ perceptions of Indian textile and clothing suppliers: Country of origin in focus

Choosing the right supplier is crucial for long-term business prospects and profitability. Thus organizational buyers are naturally very interested in how they can select the right supplier for their needs. Likewise, suppliers are interested in knowing how their customers make purchasing decisions in order to effectively sell and market to them. From the point of view of the textile and clothing (T&C) industry, regulatory changes and increasing low-cost and globalization pressures have led to the rise of low-cost production locations India and China as the world’s largest T&C producers. This thesis will examine T&C trade between Finland and India specifically in the context of non-industrial T&C products. Its main research problem asks: what perceptions do Finnish T&C industry buyers hold of India and Indian suppliers? B2B buyers use various supplier selection models and criteria in making their purchase decisions. A significant amount of research has been done into supplier selection practices, and in the context of international trade, country of origin (COO) perceptions specifically have garnered much attention. This thesis uses a mixed methods approach (online questionnaire and in-depth interviews) to evaluate Finnish T&C buyers’ supplier selection criteria, COO perceptions of India and experiences of Indian suppliers. It was found that the most important supplier selection criteria used by Finnish T&C buyers are quality, reliability and cost. COO perceptions were not found to be influential in purchasing process. Indian T&C suppliers’ strengths were found to be low cost, flexibility and a history of traditional T&C expertise. Their weaknesses include product quality and unreliable delivery times. Overall, the main challenges that need to be overcome by Indian T&C companies are logistical difficulties and the cost vs. quality trade-off. Despite positive perceptions of India for cost, the overall value offered by Indian T&C products was perceived to be low due to poor quality. Unreliable delivery time experiences also affected buyer’s reliability perceptions of Indian suppliers. The main limiting factors of this thesis relate to the small sample size used in the research. This limits the generalizability of results and the ability to evaluate the reliability and validity of some of the research instruments.

Conceptualizing and measuring human anxiety on the Internet

Since the 1990’s, the Internet has played a central role in our daily lives. The Internet is an integral part of our personal, business, family, research, entertainment, academic and social life. However, there are social implications in using the Internet that are dependent on categories such as gender, age, ethnicity and cultural attributes. This social aspect can play a detrimental role in the expression of human anxiety on the Internet. An anxiety is a complex phenomenon that requires further elaboration. Thus, the aim of this thesis is to investigate human anxiety, or specifically, whether Internet anxiety can be conceptualized and measured. This thesis utilizes literature, qualitative and quantitative research methodologies, and a triangulation validation approach to conceptualize and measure the Internet anxiety phenomenon. In particular, the aim is to explore anxiety levels of Internet participants to develop and validate an Internet anxiety scale based on earlier research on Internet anxiety. The results of the dissertation present a two phase study. In Phase I, a smaller set of studies were conducted with a limited sample size. In Phase II, the research topic was investigated using 385 participants. Based on a number of studies or experiments, the state-of-the-art discovered in this thesis is creation, design, and validation of two scales, the Self-Assessment Scale (SAS) and a Modified Internet Anxiety Scale (MIAS) for measuring users’ anxieties on the Internet. The result of this dissertation is a conceptualization and measurement of various types of Internet anxiety and measurement of affective feelings of users on the Internet. As a proof-of-concept of measuring Internet anxiety, this thesis describes the author’s implementation of three sets of tools: MyAnxiety, introducing Internet anxieties types; Intelligentia, for collecting Internet anxieties types; and MyIAControl tool, implemented as a browser plug-in, for measuring affective feelings of users on the Internet. Conclusions drawn from the results show that these empirically validated scales and tools might be useful for researchers and practitioners in understanding and measuring the Internet anxiety phenomenon further.

Savings Calculator for Centrifugal Pumps

Centrifugal pumps are one of the major energy consuming end-devices in developed coun-tries both in industrial and services sectors. According to recent studies, even 30 % of the energy used in pumping systems could be saved by more careful choosing of devices and system design. One of the most efficient and affordable ways to decrease the energy con-sumption of the pumping system is to substitute traditionally used flow control methods, like valve control, with modern variable speed drive (VSD) control. In this thesis, Microsoft Excel based program, Savings Calculator for Centrifugal Pumps (SCCP), is designed. SCCP calculates the achievable energy and financial savings when throttle control is substituted by VSD control in the pumping system. Compared to the sim-ilar existing programs, the goal is to make SCCP calculations more accurate and require less input information. Also some useful additional features are added to the designed program to make it more user friendly. The reliability of the calculations of designed program seem to vary depending on case. The results are corresponding accurately to the laboratory measurements, but there occurs high deviations in some cases, when the results are compared to the pump information specified by manufacturer. On the basis of verification in this thesis, SCCP seems to be at least as accurate as similar existing programs and it can be used as help in investment decision whether to have VSD or not.