Mixed mode testing of adhesive layer is performed with the
Mixed mode double Cantilever Beam specimen. During the experiments, the specimens are loaded by transversal and/or shear forces; seven ...different mode mixities are tested. The
J-integral is used to evaluate the energy dissipation in the failure process zone. The constitutive behaviour of the adhesive layer is obtained by a so called inverse method and fitting an existing mixed mode cohesive model, which uses a coupled formulation to describe a mode dependent constitutive behaviour. The cohesive parameters are determined by optimizing the parameters of the cohesive model to the experimental data. A comparison is made with the results of two fitting procedures. It is concluded that the constitutive properties are coupled, i.e. the peel and shear stress depend on both the peel and shear deformations. Moreover, the experiments show that the critical deformation in the peel direction is virtually independent of the mode mixity.
Objectives To examine the long-term efficacy at the 36-month follow-up of an early psychosocial counselling and support programme lasting 8–12 months for community-dwelling patients with mild ...Alzheimer's disease and their caregivers. Design Multicentre, randomised, controlled, rater-blinded trial. Setting Primary care and memory clinics in five Danish districts. Participants 330 home-dwelling patients with mild Alzheimer's disease and their primary caregivers (dyads). Interventions Dyads were randomised to receive intervention during the first year after diagnosis. Both intervention and control groups had follow-up visits at 3, 6, 12 and 36 months. Main outcome measures Primary outcomes for the patients assessed at 36-month follow-up were changes from baseline in global cognitive function (Mini-Mental State Examination), depressive symptoms (Cornell Depression Scale) and proxy-rated EuroQoL quality of life on visual analogue scale. The primary outcomes for the caregivers were changes from baseline in depressive symptoms (Geriatric Depression Scale) and self-rated EuroQoL quality of life on a visual analogue scale. The secondary outcome measures for the patient were proxy-rated Quality of Life Scale for Alzheimer's disease (QoL-AD), Neuropsychiatric Inventory-Questionnaire, Alzheimer's disease Cooperative Study Activities of Daily Living Scale, all-cause mortality and nursing home placement. Results At a 36-month follow-up, 2 years after the completion of the Danish Alzheimer Intervention Study (DAISY), the unadjusted positive effects previously detected at the 12-month follow-up in one patient primary outcome (Cornell depression score) and one patient secondary outcome (proxy-rated QoL-AD) disappeared (Cornell depression score, p=0.93; proxy-rated QoL-AD, p=0.81). No long-term effect of DAISY intervention on any other primary and secondary outcomes was found at the 36-month follow-up. Conclusions For patients with very mild Alzheimer's disease and their caregivers, an intensive, multi-component, semitailored psychosocial intervention programme with counselling, education and support during the first year after diagnosis did not show any positive long-term effect on primary and secondary outcomes. Trial registration The study was registered in the Clinical Trial Database (http://www.controlled-trials.com/ISRCTN74848736).
A large non-linear zone develops during fracture of a polyurethane adhesive bonded to steel adherends. The fracture process zone was characterised by a traction-separation law, a so-called cohesive ...law. The cohesive law was determined experimentally by the use of a J integral based approach on double cantilever beam sandwich specimens loaded with pure bending moments. The cohesive law shape was found to be highly non-linear. The cohesive stress increased with increasing separation, reached a peak and then decreased with increasing opening. The effects of loading rate and thickness of the adhesive layer on the cohesive law were investigated. An excellent agreement was found between measured strengths of bonded panels having a central notch and strength predictions based on cohesive law parameters.
A mathematical model is developed for the analysis of the fiber debonding phase of a pull-out experiment where the matrix is supported at the same end as the fiber is loaded in tension. The ...mechanical properties of the fiber matrix are described in terms of two parameters, a fracture energy for fiber matrix debonding and a frictional sliding shear stress. Results for the debond length and fiber debond displacement are compared with results from similar models for single fiber pull-out experiments where the specimen is gripped at the end opposite to the end where the fiber is pulling-out and with results for a single fiber fragmentation test.
The determination of cohesive laws for describing large scale failure process zones is discussed. Firstly, a general approach for determination of cohesive laws, by the measurement of the
J integral ...and end-opening of the cohesive zone of double cantilever beam specimens loaded with pure bending moments, is described. Next, two case stories are reviewed: failure of adhesive joints and splitting of a unidirectional carbon fibre/epoxy composite. For the adhesive joints, measured failure strengths of bonded panels having a central notch were found to in very good agreement with predictions from cohesive law parameters determined on test specimens. For the problem of splitting of unidirectional composites, micromechanisms were observed in situ during cracking. A cohesive law shape, predicted by a micromechanics model, was found to agree well with macroscopic cohesive law determined by the
J integral approach. The cohesive law was used for predicting effect of specimen shape on strength; predictions were confirmed by experiments. Finally, some ideas regarding determination of mixed mode cohesive laws are discussed.
A gliding arc enables selective chemical process with high productivity due to its high degree of non-equilibrium and high energy density simultaneously, and thus can be preferably used for a variety ...of industrial applications such as gas cleaning, pollution control, fuel conversion, hydrogen production, and surface treatment. However, the application for adhesion improvement of structural materials has been rarely reported. In the present work, glass fibre reinforced polyester plates were treated using atmospheric pressure gliding arcs with high speed air flow for adhesion improvement with vinylester resin. It is found that the treatment increased the density of oxygen-containing polar functional groups at the composite surfaces, the polar component of the surface energy, and adhesive strength with a vinylester resin. The treatment effect highly depended on the temperatures of the electrodes and the discharge.
The fracture properties of all-cellulose composites without matrix were studied using Double Cantilever Beam (DCB) sandwich specimens loaded with pure monotonically increasing bending moments, which ...give stable crack growth. The experiments were conducted in an environmental scanning electron microscope to a) perform accurate measurements of both the fracture energy for crack initiation and the fracture resistance and b) observe the microscale failure mechanisms especially in the the wake of the crack tip. Since the mechanical behaviour of the all-cellulose composites was non-linear, a general method was first developed to obtain fracture resistance values from the DCB specimens taking into account the non-linear material response. The binderfree all-cellulose composites were prepared by a mechanical refinement process that allows the formation of intramolecular bonds between the cellulose molecules during the drying process. Defibrilation of the raw cellulose material is done in wet medium in a paper-like process. Panels with different refining time were tested and it was found than an increase in fibre fibrillation results in a lower fracture resistance.
Reliable assessment of structural integrity of fuel cells requires the knowledge of the mechanical properties of their individual components, in particular the fracture toughness. A technique is ...presented to measure the critical energy-release rate/fracture toughness of thin ceramic layers such as the anode material (NiO–YSZ) in a fuel cell. The approach involves a new specimen geometry which consists of a thin ceramic glued onto thick steel beams to form a double cantilever beam (DCB) specimen. The fracture toughness values, measured from truly sharp cracks, are obtained over a range of applied energy-release rates: from crack growth initiation to fast fracture. The fracture toughness is measured to be 1.97
±
0.13
MPa
m
at crack growth initiation.
PDF
