Crack tip plastic zone under Mode I, Mode II and mixed mode (I+II) conditions

Ayatollahi, M.R.,Sedighiani, Karo Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative T-stresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

Temperature effects on brittle fracture in cracked asphalt concretes

Ayatollahi, Majid-Reza,Pirmohammad, Sadjad Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.1

Cracking at low temperatures is one of the frequently observed modes of failure in asphalt concretes. In this investigation, fracture tests were performed on cracked asphalt concrete subjected to pure mode I and pure mode II loading at different subzero temperatures. An improved semi-circular bend (SCB) specimen containing a vertical crack was used to conduct the experiments. The SCB specimens produced from the gyratory compacted cylindrical samples were compressively loaded, and critical stress intensity factors, $K_{If}$ and $K_{IIf}$, were then calculated using peak loads obtained from the tests. The experimental results showed that with decreasing the temperature, mode I and mode II critical stress intensity factors increased first but below a certain temperature they both decreased. It was also found that at a fixed temperature, the mode II fracture resistance of the asphalt concrete was higher than its mode I fracture resistance.

Brittle fracture analysis of the offset-crack DCDC specimen

Ayatollahi, M.R.,Bagherifard, S. Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.3

Applications of fracture mechanics in the strength analysis of ceramic materials have been lately studied by many researchers. Various test specimens have been proposed in order to investigate the fracture resistance of cracked bodies under mixed mode conditions. Double Cleavage Drilled Compression (DCDC) specimen, with a hole offset from the centerline is a configuration that is frequently used in subcritical crack growth studies of ceramics and glasses. This specimen exhibits a strong crack path stability that is due to the strongly negative T-stress term. In this paper the maximum tensile stress (MTS) criterion is employed for investigating theoretically the initiation of brittle fracture in the DCDC specimen under mixed mode conditions. It is shown that the T-stress has a significant influence on the predicted fracture load and the crack initiation angle. The theoretical results suggest that brittle fracture in the DCDC specimen is controlled by a combination of the singular stresses (characterized by KI and KII) and the non-singular stress term, T-stress.

New formulation for vibration analysis of Timoshenko beam with double-sided cracks

Ayatollahi, M.R.,Hashemi, R.,Rokhi, H. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.

Patient Accounting Systems: Are They Fit with the Users’ Requirements?

Haleh Ayatollahi,Zahra Nazemi,Hamid Haghani 대한의료정보학회 2016 Healthcare Informatics Research Vol.22 No.1

Objectives: A patient accounting system is a subsystem of a hospital information system. This system like other informationsystems should be carefully designed to be able to meet users’ requirements. The main aim of this research was to investigateusers’ requirements and to determine whether current patient accounting systems meet users’ needs or not. Methods: Thiswas a survey study, and the participants were the users of six patient accounting systems used in 24 teaching hospitals. Astratified sampling method was used to select the participants (n = 216). The research instruments were a questionnaire and a checklist. The mean value of ≥3 showed the importance of each data element and the capability of the system. Results: Generally, the findings showed that the current patient accounting systems had some weaknesses and were able to meet between 70% and 80% of users’ requirements. Conclusions: The current patient accounting systems need to be improved to be able to meet users’ requirements. This approach can also help to provide hospitals with more usable and reliable financial information.

Anti-plane analysis of functionally graded materials weakened by several moving cracks

Mojtaba Ayatollahi,Rasoul Moharrami 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11

This paper considers several finite moving cracks in a non-homogeneous material. The shear modulus and mass density of the plane are considered for a class of functional forms for which equilibrium equation has analytical solutions. The distributed dislocation technique is used to carry out stress analysis in a non-homogeneous plane containing moving cracks under anti-plane loading. The solution of a moving screw dislocation is obtained in a non-homogeneous plane by means of Fourier transform method. The stress components reveal the familiar Cauchy singularity at the location of dislocation. The solution is employed to derive integral equations for a plane weakened by moving cracks. Finally several examples are solved to show the effects of the material non-homogeneity and speed of cracks on the stress intensity factors.

Integrating Genetic Data into Electronic Health Records: Medical Geneticists’ Perspectives

Haleh Ayatollahi,Seyedeh Fatemeh Hosseini,Morteza Hemmat 대한의료정보학회 2019 Healthcare Informatics Research Vol.25 No.4

Objectives: Genetic disorders are the main causes of many other diseases. Integrating genetic data into Electronic Health Records (EHRs) can facilitate the management of genetic information and care of patients in clinical practices. The aim of this study was to identify the main requirements for integrating genetic data into the EHR system from the medical geneticists’ perspectives. Methods: The research was completed in 2018 and consisted of two phases. In the first phase, the main requirements for integrating genetic data into the EHR system were identified by reviewing the literature. In the second phase, a 5-point Likert scale questionnaire was developed based on the literature review and the results derived from the first phase. Then, the Delphi method was applied to reach a consensus about the integration requirements. Results: The findings of the first phase showed that data elements, including patients’ and healthcare providers’ personal data, clinical and genetic data, technical infrastructure, security issues and functional requirements, should be taken into account before data integration. In the second phase, a consensus was reached for most of the items (mean ≥3.75). The items with a mean value of less than 2.5 did not achieve a consensus and were removed from the final list. Conclusions: The integration of genetic data into the EHRs can provide a ground for increasing accuracy and precision in the diagnosis and treatment of genetic disorders. Such integration requires adequate investments to identify users’ requirements as well as technical and non-technical issues

Confirmation of Expectations and Satisfaction with Hospital Information Systems: A Nursing Perspective

Haleh Ayatollahi,Mostafa Langarizadeh,Habib Chenani 대한의료정보학회 2016 Healthcare Informatics Research Vol.22 No.4

Objectives: This study aimed to compare nurses’ satisfaction with, and expectations of, hospital information systems in two teaching hospitals. Methods: This was a survey study, which was completed in 2014. The potential participants were 267 nurses who worked in two teaching hospitals and used the same hospital information system. Data were collected using two questionnaires. Both questionnaires were examined in terms of content validity and reliability. Results: The results showed that, for a majority of nurses, their expectations of the system were not met in either hospital. Moreover, there was a significant association between the nurses’ expectations and the perceived usefulness of the systems (p < 0.001), between the nurses’ expectations and their satisfaction with the systems (p < 0.001), and between the perceived usefulness and nurses' satisfaction with the systems (p < 0.001). Conclusions: The results suggested that, apart from the technical issues of implementing clinical information systems, non-technical factors should be taken into account. Among them, the nature of clinical tasks and the organizational culture require more attention to allow a successful system to be designed and implemented.

Crack tip plastic zone under Mode I, Mode II and mixed mode (I+II) conditions

M.R. Ayatollahi,Karo Sedighiani 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.5

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative Tstresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

Temperature effects on brittle fracture in cracked asphalt concretes

Majid-Reza Ayatollahi,Sadjad Pirmohammad 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.1

Cracking at low temperatures is one of the frequently observed modes of failure in asphalt concretes. In this investigation, fracture tests were performed on cracked asphalt concrete subjected to pure mode I and pure mode II loading at different subzero temperatures. An improved semi-circular bend (SCB)specimen containing a vertical crack was used to conduct the experiments. The SCB specimens produced from the gyratory compacted cylindrical samples were compressively loaded, and critical stress intensity factors, KIfand KIIf, were then calculated using peak loads obtained from the tests. The experimental results showed that with decreasing the temperature, mode I and mode II critical stress intensity factors increased first but below a certain temperature they both decreased. It was also found that at a fixed temperature, the mode II fracture resistance of the asphalt concrete was higher than its mode I fracture resistance.