Finite Element Analysis of Adhesively Bonded Lap Joints

Adhesive bonding is a preferred method of joining aerospace structural components, since it provides fewer points of stress concentration compared to fastener joints. Geometrically nonlinear analysis of adhesively bonded lap joints is presented in this paper using both linear and non-linear material properties of the adhesive. The numerical results show beneficial effects of material non-linear behaviour of the adhesive which decrease the stress concentration at the ends of the lap Length. This paper also presents the estimation of strain-energy-release rate components in the presence of debond in the adhesive. The studies have relevance in structural integrity assessment of the joints

Failure prediction of adhesively bonded lap joints between metal and composite adherends

Most of the modern civilian or military aircrafts use advanced composite materials for their primary structural components, in addition to metals. The components are joined together by using either fastener or adhesively bonded joints. But with the introduction of composite materials in aircraft industries, adhesively bonded lap joints are most preferred. This is due to the fact that they develop smooth load transfer and fewer points of stress concentration as compared to fastener joints. The failure prediction of such joints is extremely important, to avoid catastrophic failures during aircraft service period. In the present investigation, an adhesively bonded lap joint between metal-composite (i.e., Al 2024-T3/CFRP) adherends bonded with Redux 319-A adhesive has been analyzed using finite element method considering geometric non-linearity and incorporating adhesive material nonlinear behavior. The failure has been predicted using plastic zone size criterion of adhesive material, which is innovative approach of this study. Also, experimental program is carried out on such joints to correlate with the predicted failure load obtained from numerical model. In this study, the failure of joint is assumed to take place due to adhesive failure only. Plastic zone size in adhesive at failure load of joint is taken as 15 % of the lap length as established from the previous work of the authors. It is observed that the failure load of the adhesively bonded lap joint between composite-metal adherends as obtained from numerical model is well compared with that obtained from experimental study. Results are discussed

Electromechanical and Dynamic Characterization of In-House-Fabricated Amplified Piezo Actuator

A diamond-shaped amplified piezo actuator (APA) fabricated using six multilayered piezo stacks with maximum displacement of 173 μm at 175V and the amplification factor of 4.3. The dynamic characterization of the actuator was carried out at different frequencies (100 Hz–1 kHz) and at different AC voltages (20V–40V). The actuator response over this frequency range was found neat, without attenuation of the signal. Numerical modeling of multilayered stack actuator was carried out using empirical equations, and the electromechanical analysis was carried out using ABAQUS software. The block force of the APA was 81 N, calculated by electromechanical analysis. This is similar to that calculated by dynamic characterization method

Finding Pairwise Intersections Inside a Query Range

We study the following problem: preprocess a set O of objects into a data structure that allows us to efficiently report all pairs of objects from O that intersect inside an axis-aligned query range Q. We present data structures of size $O(n({\rm polylog} n))$ and with query time $O((k+1)({\rm polylog} n))$ time, where k is the number of reported pairs, for two classes of objects in the plane: axis-aligned rectangles and objects with small union complexity. For the 3-dimensional case where the objects and the query range are axis-aligned boxes in R^3, we present a data structures of size $O(n\sqrt{n}({\rm polylog} n))$ and query time $O((\sqrt{n}+k)({\rm polylog} n))$. When the objects and query are fat, we obtain $O((k+1)({\rm polylog} n))$ query time using $O(n({\rm polylog} n))$ storage

Feelings of dual-insecurity among European workers: A multi-level analysis

This article analyses European Social Survey data for 22 countries. We assess the relationship between feelings of employment and income insecurity (dual-insecurity) among workers and national flexicurity policies in the areas of lifelong learning, active labour market policy, modern social security systems and flexible and reliable contractual arrangements. We find that dual-insecurity feelings are lower in countries that score better on most flexicurity polices, but these effects are in all cases outweighed by levels of GDP per capita. Thus feelings of insecurity are reduced more by the affluence of a country than by its social policies. However, affluence is strongly correlated with the policy efforts designed to reduce insecurity, especially active labour market policies and life-long learning, two policy areas that are threatened with cuts as a result of austerity

Strength Prediction of Adhesively Bonded Joints using Plastic Zone Size Criterion

The prediction of the strength of adhesively bonded joints has been an issue of considerable interest in literature. This exercise requires numerical techniques combined with experimental programs and matching the two to arrive at a viable criterion. The configurations used for the study are single lap adhesively bonded joints between (i) aluminium (Al) – aluminium (Al) and (ii) carbon fibre reinforced composite (CFRP) and aluminium adherends with Redux-319A epoxy. Geometric and material non-linear finite element analysis was conducted using the NASTRAN software package to establish the proposed plastic zone size (PZS) failure criterion. On the same configuration both experimental program for joint strength and numerical analysis were conducted. The plastic zone size corresponding to failure load was initially estimated from Al-Al joints. The same value was used to predict failure load for CFRP-Al bonded joint. The average experimental value and numerical predictions for CFRP-Al joints matched within 7%. This study suggests an alternative method of strength prediction of adhesively bonded single lap joint in presence of inelastic behaviour of adhesive material

Knowledge, attitude, and infection control practices of two tertiary hospitals in Port‑Harcourt, Nigeria

Background: Surgical site infections (SSIs) are a significant cause of morbidity, emotional stress and financial cost to the affected patients and health care institutions, and infection control policy has been shown to reduce the burden of SSI in several health care institutions. This study assessed the effects of the implementation of the policy in a tertiary hospital in Port Harcourt, Nigeria.Materials and Methods: A cross‑sectional, comparative study design was used for the study, with data collected using a structured questionnaire and guided observation of doctors and nurses involved in the management of patients that had caesarean sections in two comparable tertiary hospitals in Port Harcourt‑the University of Port Harcourt Teaching Hospital (UPTH) and the Braithwaite Memorial Specialist Hospital (BMSH).Results: There were no statistically significant differences in the designations and length of practice of the respondents in both hospitals (P = 0.77). However, 63.64% of the respondents in UPTH were aware of the infection control committee, compared with none in BMSH. The appropriate timing for the administration of prophylactic antibiotics, and for the removal of the hair at the incision site were observed by 57.58% and 69.69% respectively of the respondents in UPTH, compared with 22.86% (P = 0.00) and 0.00% (P = 0.02) in BMSH. The reasons given by the respondents in UPTH for nonadherence to the infection control policy include poor supervision (39.39%) and lack of in‑service training (21.21%), while the respondents in BMSH gave reasons that include inadequate supply of consumables (34.29%) and absence of a hospital’s policy on infection control (22.88%).Conclusion: The implementation of the infection control policy resulted in some improvements in certain infection control practices.Keywords: Adherence, hospital infection control committee, hospital infection control policy, Nigeria, Port Harcourt, practice, surgical site infectio

Growth of Epitaxial Oxide Thin Films on Graphene

The transfer process of graphene onto the surface of oxide substrates is well known. However, for many devices, we require high quality oxide thin films on the surface of graphene. This step is not understood. It is not clear why the oxide should adopt the epitaxy of the underlying oxide layer when it is deposited on graphene where there is no lattice match. To date there has been no explanation or suggestion of mechanisms which clarify this step. Here we show a mechanism, supported by first principles simulation and structural characterisation results, for the growth of oxide thin films on graphene. We describe the growth of epitaxial SrTiO3 (STO) thin films on a graphene and show that local defects in the graphene layer (e.g. grain boundaries) act as bridgepillar spots that enable the epitaxial growth of STO thin films on the surface of the graphene layer. This study, and in particular the suggestion of a mechanism for epitaxial growth of oxides on graphene, offers new directions to exploit the development of oxide/graphene multilayer structures and devices

An observational study to explore the Samprapti Ghatakas in Hypothyroidism

Background: Hypothyroidism is the most common functional disorder of the thyroid gland. It is a hypometabolic clinical state resulting from inadequate production of thyroid hormones for prolonged periods. The prevalence of this disease in India is 6% and more than 10 million cases per year are reported. It is a multisystemic disorder which has a wide range of clinical symptoms. This condition is not mentioned in Ayurveda classics by any specified name. In Ayurveda, determining the elements that contribute to Samprapti is essential in developing a treatment plan. Hence, the current study attempts to evaluate the Samprapti Ghatakas and as a result, formulate probable Samprapti. Objectives: To study and explore the Samprapti Ghatakas of hypothyroidism and to propose possible Samprapti. Methods: The study was conducted in 100 cases of hypothyroidism between the age of 16 to 70 years. A case proforma was prepared which includes history taking, physical signs and symptoms and required examination. The calculations were done in Microsoft excel and the values obtained were assessed on the basis of percentage of individual parameters in relation with Samprapti Ghatakas of hypothyroidism. Results: Kapha and Vata are the main Doshas involved in the Samprapti. Important Dooshyas are Rasa, Meda. Agni involved is Dhatwagni and the disease is caused primarily due to Dhatwagnimandya. Udakavaha, Annavaha, Medovaha, Swedavaha, Purishavaha, Rasavaha are the main Srotas involved with Sanga type of Srotodushti. Udbhava Sthana can be considered as Amashaya; Sanchara Sthana, Vyakta Sthana and Adhishtana is Sarva Shareera. All the three Rogamarga are involved