Search results

Stress state has a major influence on different phenomena, namely those involving diffusion and plastic deformation (like crack closure and high‐temperature fatigue crack growth, void formation or ductile fracture). The isolation of plane stress and plane strain states is crucial in fundamental studies of material behavior. The isolation of plane stress state is achieved with thin specimens, whilst the isolation of plane strain state is usually done increasing the thickness or introducing lateral grooves. The purpose of this paper is to propose a specimen geometry able to isolate the plane strain state, based on the standard M(T) geometry.

A numerical study was carried out aiming at obtaining a stress triaxiality parameter, h, as a function of different geometrical features of the specimen, such as the notch radius, notch depth and specimen thickness.

Results show that a pure plane strain state is achievable (i.e. 97 percent of specimen thickness has h>0.97) if a specimen with optimized geometrical features is used, which corresponds to a notch radius of 0.5 mm, a notch depth of 1 mm and a total specimen thickness of 12.56 mm.

This type of specimen geometry is a simple and efficient alternative to other common approaches used to obtain pure plain strain conditions for experimental purposes.

The purpose of this paper is to study the influence of multiaxial loading composed with different frequencies between the axial and torsional components in 42CrMo4 concerning fatigue life and early crack growth orientation.

Biaxial fatigue tests were carried out by a biaxial servo‐hydraulic machine, considering different loading paths and different frequencies between the normal and shear stress components in 42CrMo4. Theoretical estimations for fatigue life and early crack growth orientation were performed by applying various critical plane models. In addition, fractographic analysis of the fracture surfaces was carried out. The estimated results are compared with experimental results.

Significant effects were observed of the different frequency between the axial and torsion components on fatigue life and early crack growth orientation. The critical plane models based on shear mode give better estimations when compared with experimental results.

The paper shows that improved fatigue design can be achieved by considering the influence of different frequencies in multiaxial loadings.

The purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.

The linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.

As long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.

In future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.

The paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

The purpose of this paper is to perform a numerical assessment of two recently proposed extensions of the Gurson‐Tveegard‐Needleman ductile damage constitutive model under low stress triaxiality.

One of the most widely used ductile damage models is the so‐called Gurson‐Tveegard‐Needleman model, commonly known as GTN model. The GTN model has embedded into its damage formulation the effects of nucleation, growth and coalescence of micro‐voids. However, the GTN model does not include void distortion and inter‐void linking in the damage evolution. To overcome this limitation, some authors have proposed the introduction of different shear mechanisms based on micromechanical grounds or phenomenological assumptions. Two of these constitutive formulations are reviewed in this contribution, numerically implemented within a quasi‐static finite element framework and their results critically appraised.

Through the analysis of the evolution of internal variables, such as damage and effective plastic strain, obtained by performing a set of numerical tests using a Butterfly specimen, it is possible to conclude that the extended GTN models are in close agreement with experimental evidence.

Even though the results obtained with the modified GTN models have shown improvements, it can also be observed that both shear mechanisms have inherent limitations in the prediction of the location of fracture onset for some specific stress states.

From the results reported, it is possible to identify some shortcomings in the recently proposed extensions of the GTN model and point out the direction of further improvements.

The last two decades have witnessed a tremendous growth in the body of literature addressing the importance and the impact of contracting and public procurement within the context of devolution of government. The austere budgetary and financial outlooks of the future suggest that the significance of the area will only continue to grow. As such, generating explanatory frameworks, within dimensions such as decisionmaking and accountability in public procurement, becomes crucial. Drawing from original research this article suggests one possible frame for understanding administrative decision-making in complex environments. Based on semi-structured interviews with public procurement specialists, the study identifies two decision-making patterns— broker and purist. It is asserted that the decision-making dynamics exhibited by administrators are contingent on their perceptions regarding environmental instability, in particular the political volatility surrounding their work.

The last two decades have witnessed a tremendous growth in the body of literature addressing the importance and the impact of contracting and public procurement within the context of devolution of government. The austere budgetary and financial outlooks of the future suggest that the significance of the area will only continue to grow. As such, generating explanatory frameworks, within dimensions such as decisionmaking and accountability in public procurement, becomes crucial. Drawing from original research this article suggests one possible frame for understanding administrative decision-making in complex environments. Based on semi-structured interviews with public procurement specialists, the study identifies two decision-making patterns− broker and purist. It is asserted that the decision-making dynamics exhibited by administrators are contingent on their perceptions regarding environmental instability, in particular the political volatility surrounding their work.

The paper aims to evaluate the state of the literature on public procurement through examination of the works published in the Journal of Public Procurement from 2001 to 2014. 231 research outputs were collected and analyzed (with regard to, e.g., the background theory used, research method, and content of the papers), providing a overview of prior research topics and findings and identifying main gaps in the existing literature. This type of study is unique, as a broad literature review related to public procurement does not currently exist; therefore, the work has been designed with the intention to a) synthetize the prior research on public procurement; b) provide researchers with a structural framework in which future research on public procurement topics may be oriented; c) identify promising and active areas for future research.

The contribution of planning in facilitating an efficient and effective performance of public sector organizations is generally undisputed in both developed and developing countries. Its contribution can be at both central and local government levels of public sector management. This article examines the relationship between procurement planning and accountability of local government procurement systems in Uganda. The findings arose from a study that was conducted among 99 local government stakeholders selected from 11 Districts of Uganda, using a correlation research design. The data was analyzed using principal component factor analysis that aimed at identifying the critical components of procurement planning and accountable local governments systems in Uganda. Consequently, correlation analysis to establish the direction and magnitude to which the two variables were related was conducted and results are presented. The findings revealed a significant positive relationship between procurement planning and accountable local government procurement systems in Uganda. These results are compared to international research findings, and suggestions are offered for management, policy making, future research and efficient accountable local government operations.