Experimental and analytical study of cracks under biaxial fatigue

Most mechanical components experience multi-axial cyclic loading conditions during service. Experimental analysis of fatigue cracks under such conditions is not easy and most works tend to focus more on the simpler but less realistic case of uni-axial loading. Consequently, there are many uncertainties related to the load sequence effect that are now well known and are not normally incorporated into the growth models. The current work presents a new methodology for evaluating overload effect in biaxial fatigue cracks. The methodology includes evaluation of mixed-mode (KI and KII) stress intensity factor and the Crack Opening Displacement for samples with and without overload cycle under biaxial loading. The methodology is tested under a range of crack lengths. All crack-tip information is obtained with a hybrid methodology that combines experimental full-field digital image correlation data and Williams' elastic model describing the crack-tip field.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

DOES HUMAN CAPITAL STIMULATE INVESTMENT IN PHYSICAL CAPITAL? EVIDENCE FROM A COST SYSTEM FRAMEWORK

The direct effect of human capital on economic growth has been widely analysed in the economic literature. This paper, however, focuses on its indirect effect as a stimulus for private investment in physical capital. The methodological framework used is the duality theory, estimating a cost system aggregated with human capital. Empirical evidence is given for Spain for the period 1980-2000. We provide evidence on the indirect effect of human capital in making private capital investment more attractive. Among the main explanations for this process, we observe that higher worker skill levels enable higher returns to be extracted from investment in physical capital.

Regional returns to physical capital: are they conditioned by educational attainment?

This paper provides novel empirical evidence of the indirect effect of educational attainment on regional economic growth, through its influence on the profitability of investment in physical capital. We test the hypothesis that the regional heterogeneity of the return to physical capital can be directly related to the existing heterogeneity in the educational attainment of workers. The results for the Spanish case support our hypothesis that the higher the educational attainment of workers the greater the returns on investment in physical capital. In fact, this effect seems to be sufficiently strong to have counterbalanced the traditional mechanism of decreasing returns to capital accumulation.returns to capital, human capital, productivity, cost system

Do innovation and human capital explain the productivity gap between small and large firms?

Empirical evidence is compelling that large firms are more productive than small firms. The hypothesis in this paper is that the productivity differences between small and large firms are associated with two of the main determinants of a firm’s performance: the human and technological capital that firms incorporate. We suggest that the contribution of these factors in explaining the size of the productivity gap might not only be due to the fact that large firms make a more extensive use of them, but also because large firms obtain higher returns from their investment in human and technological capital. The evidence we obtain for a comprehensive sample of Spanish manufacturing firms (1990-2002) supports this hypothesis, which has important implications for the effectiveness of policies designed to improve productivity in SMEs by stimulating innovation and the use of more skilled workers.total factor productivity; innovation; skilled labour; firm size.

The principal’s dilemma

A recurrent dilemma in team management is to select between a team-based and an individual based wage scheme. We explore such a dilemma in a simple model of production in teams, in which the team members may differ in their effort choices and qualification. We show that, in spite of enhancing output as the basis for payment, a team-based wage scheme might be less profitable for the principal than an individual-based wage scheme. We also highlight a deep misalignment between designing optimal (output-based) incentives for a team and treating its members impartially. Finally, upon introducing the possibility of liquidity constraints in our model, we provide rationale for the so-called "rich get richer" hypothesis.team production, management, incentives, effort

Decomposing differences in total factor productivity across firm size.

This paper investigates the extent to which the gap in total factor productivity between small and large firms is due to differences in the endowment of factors determining productivity and to the returns associated with these factors. We place particular emphasis on the contribution of differences in the propensity to innovate and in the use of skilled labor across firms of different size. Empirical evidence from a representative sample of Spanish manufacturing firms corroborates that both differences in endowments and returns to innovation and skilled labor significantly contribute to the productivity gap between small and large firms. In addition, it is observed that the contribution of innovation to this gap is caused only by differences in quantity, while differences in returns have no effect; in the case of human capital, however, most of the effect can be attributed to increasing differences in returns between small and large firms.Total Factor Productivity, skilled labor, innovation, firm size, Oaxaca decomposition