Mechanical properties and microstructure of friction stir welded tailor-made blanks

This paper studies the microstructural features and mechanical properties of friction stir welds with dissimilar alloys and different thicknesses. The welds are produced in five different thickness/material combinations from 2024-T3 and 7075-T6 sheets with different thicknesses. A parametric study is conducted to optimize the welding parameters such that the different configurations can be compared. The paper is divided into two chapters: microstructural features and mechanical properties. In the first chapter, a study of the chemical composition and microstructure of the welds shows that a narrow chemical mixing zone is present in the dissimilar-alloy welds and that the stirring zone embodies the union rings and exhibits heterogeneous texture for most configurations. Study of the hardness, tensile properties and fracture surfaces in the second chapter shows that an asymmetric softened region, which is harder at the advancing side and extends more into the retreating side, is formed in the stirring zone and that the mechanical properties decrease as the thickness ratio increases. The fracture was partially ductile and partially brittle for all configurations.     

Effect of plasma treatment and electron beam radiations on the strength of nanofilled adhesive‐bonded joints

This investigation highlights the adhesion performance of carbon fiber‐ and glass fiber‐reinforced polyphenylene sulfide when joined by high‐performance neat epoxy adhesive and nanofilled epoxy adhesive. A significant increase in the surface energy of these materials is observed after the surface modification with atmospheric plasma treatment. An increase in surface roughness is observed after exposing the surface to plasma. Lap shear testing of untreated and plasma‐treated joints is carried out to correlate the improvement in adhesion properties with the joint strength. A considerable increase in joint strength is observed when the surfaces of these materials are modified by atmospheric pressure plasma. There is a further increase in joint strength when the composites are joined by nanofilled epoxy adhesive, and subsequent exposure to electron beam radiations results in minor increase in the joint strength. Finally, the fractured surfaces of the joints are examined and the analysis is performed. POLYM. ENG. SCI., 50:1505–1511, 2010. © 2010 Society of Plastics Engineers     

Adaptive conjoint analysis to determine perceived risk factors of farmers, veterinarians and AI technicians for introduction of BHV1 to dairy farms

A study was carried out to determine the possibility of a more-closed farming system for (Dutch) dairy farms. The objective of the study was to provide effective and economically profitable management advice for improving the animal-health status of farms. Management measures will only be successfully applied if supported by farmers and their advisors (such as veterinarians). Therefore, the perception of farmers and advisors of the importance of various risk factors for the introduction of diseases to a farm was determined by using bovine herpes virus type 1 (BHV1) as an example. As part of the study, an evening-long workshop was organized and run thrice. In total, 49 farmers, veterinarians and AI technicians participated in these workshops. The computerized questionnaire technique was based on adaptive conjoint analysis (ACA). ACA has the advantage that participants can work with a large number of risk factors in a relatively short period of time. Another advantage of ACA (compared with standard questionnaires) is that the answers from each participant can be checked with regard to consistency with respect to the importance assigned to them. Data from participants with inconsistent responses can be excluded from further analyses. The results of the ACA interview were compared with the risk factors reported in the literature as being associated with BHV1 status (e.g. purchase of cattle, participation in cattle shows) and with farmers' actual management to prevent the introduction of diseases. The workshop participants were all operating in the dairy sector and they seemed well aware of the risk of direct animal contacts for the introduction of BHV1. Farmers thought visitors to be more risky than did AI technicians and (especially) veterinarians. Farmers who purchased cattle or participated in cattle shows were of the opinion that the risks of direct animal contacts were more important than did farmers who were not involved in those practices. Farmers whose farms were BHV1-positive (and participated in cattle shows more often) thought the risk of participation smaller than did farmers with BHV1-negative farms.     

The Dynamics of Indonesia's Urbanisation, 1980-2006

This study examines continuity and change in patterns of Indonesia's urbanisation during the boom economy until the decentralisation era, using data mainly from the National Population Census 1980-2000 and from the Village Potential (PODES) 2006. Urbanisation in Indonesia is still characterised by a heavy concentration of the urban population in a few large cities, notably the Jakarta Metropolitan Area (JMA), which might reflect an integration of Jakarta into the global economy. It might also reflect an interurban disparity, between large and smaller cities. The population on the fringes of large cities is growing rapidly, while in the inner cities it is increasing at a very low rate of growth. Urban spatial development in Java is shaping belts, which connect many of the large cities. The intermediate cities and small towns on the outer islands have a relatively higher population growth rate compared with those in Java, which might suggest that those towns and cities are playing a more significant role in regional development.     

A virus-based single-enzyme nanoreactor

Most enzyme studies are carried out in bulk aqueous solution, at the so-called ensemble level, but more recently studies have appeared in which enzyme activity is measured at the level of a single molecule, revealing previously unseen properties. To this end, enzymes have been chemically or physically anchored to a surface, which is often disadvantageous because it may lead to denaturation. In a natural environment, enzymes are present in a confined reaction space, which inspired us to develop a generic method to carry out single-enzyme experiments in the restricted spatial environment of a virus capsid. We report here the incorporation of individual horseradish peroxidase enzymes in the inner cavity of a virus, and describe single-molecule studies on their enzymatic behaviour. These show that the virus capsid is permeable for substrate and product and that this permeability can be altered by changing pH.     

Thermotropic liquid crystalline polymers as protective coatings for aerospace

Liquid crystalline polymers (LCPs) have potential as multifunctional, environmentally friendly coatings for aerospace, overcoming the disadvantages of current materials. Their use, however, has been hindered mainly by their poor adhesion strength. The present work studies novel liquid crystalline thermosetting polymers (LCTs), which can overcome the disadvantages of commercial LCPs for protective coatings in aerospace applications. Phenylethynyl terminated liquid crystalline oligomers based on 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) were synthesized and melt-pressed on grit-blasted aluminum to obtain 25 μm and 80 μm thick coatings. The presence of coating defects and curing kinetics were investigated, and the adhesion, mechanical properties and environmental resistance were compared with a commercial LCP reference material (Vectra^®). The LCTs showed highly improved adhesion; moreover, fully cured LCTs are harder and stiffer than commercial LCPs, which are expected to increase their wear and impact resistance. The coatings showed no swelling, peeling, or blistering after 500 h of full immersion in fluids such as jet fuel and turbine oil; furthermore, LCTs resisted 1000 h in corrosive fog (salt-spray) and hot moisture. Exposed samples retained their hardness, modulus, and pull-off strength, evidencing the outstanding chemical resistance of these LCTs. Our findings showed the potential of LCTs as protective and wear resistant coatings, particularly in the aggressive environments of aerospace applications. However, results suggest that exposed coating/substrate interfaces constitute paths for environmental attack. Further research aims at elucidating the possible mechanisms.     

Thermal,morphological, and mechanical characterization of novel carbon nanofiber‐filled bismaleimide composites

Novel carbon nanofiber (CNF) ‐filled bismalemide composites were fabricated by a thermokinetic mixing method. The thermal and mechanical properties of composites containing 1 wt % and 2 wt % CNFs were investigated. Thermogravimetric analysis demonstrated that minimal improvement in thermal stability of the nanocomposites was obtained by the addition of CNFs. Dynamic mechanical analysis showed an increase in storage modulus (E′) and glass transition temperature (T_g) upon incorporation of nanofibers. Limiting oxygen index (LOI) has also been found to increase with incorporation of CNFs. Morphological studies of fractured surfaces of the composites has been carried out by scanning electron microscopy to determine the effect of fiber content and dispersion on the failure mechanism. In general, good dispersion was observed, along with agglomeration at some points and some fiber matrix interfacial debonding. A decrease in mechanical strength has been observed and debonding was found as the main failure mechanism. Further research outlook is also presented. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The mechanical behavior of adhesively bonded tailor-made blanks

Joining (or welding) and subsequent forming of sheets with different thicknesses and/or materials into single-sheet assemblies called tailor-made blank (TMB) is a promising weight-saving strategy for both the automotive and aircraft industries. Although this technology is widely accepted in the automotive industry, it has yet to be applied in the aircraft industry. This is partly because the high-strength aluminum alloys used in the aircraft industry are sensitive to the high welding temperatures. Adhesive bonding is a promising alternative joining method for fabrication of tailor-made blanks in the aircraft industry. In this paper, the mechanical behavior of adhesively bonded tailor-made blanks is studied from both experimental and numerical viewpoints. Transition line is defined as the boundary between two different thicknesses present in the TMB. Two different forming directions, one in parallel with the transition line and one perpendicular to that, are considered. Tensile testing of the specimens from each category is carried out and finite element method (FEM) models are used to simulate the mechanical behavior of the specimens during the test. It is shown that when loading direction is perpendicular to the transition line, metal failure is preceded by decohesion. The adhesive layer is modeled by using the cohesive interface elements with the capability of simulating the damage initiation and evolution mechanisms of adhesives. The experimental and numerical results are compared and are shown to be in a good agreement. It is shown that the capacity of TMBs for in-plane plastic straining is limited. It is therefore recommended that the forming process should be designed such that in-plane plastic straining is minimized.     

Delamination growth in Fibre Metal Laminates under variable amplitude loading

This paper presents the experimental and analytical investigation of the effect of variable amplitude (VA) load sequences on delamination behavior in Fibre Metal Laminates (FMLs). Delamination tests were performed and results are compared with linear damage accumulation predictions. Scanning Electronic Microscopy (SEM) was used to analyse the delaminated surfaces to study the delamination growth rate under VA loading in more detail. The correlation between test results and predictions highlighted the absence of load sequence and interaction effects in delamination growth rate under VA loading. This correlation is supported by the SEM observations.