Microencapsulated dicyclopentadiene (DCPD) healing agent and Grubbs' Ru catalyst are incorporated into an epoxy matrix to produce a polymer composite capable of self-healing. The fracture toughness ...and healing efficiency of this composite are measured using a tapered double-cantilever beam (TDCB) specimen. Both the virgin and healed fracture toughness depend strongly on the size and concentration of microcapsules added to the epoxy. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of DCPD-filled urea-formaldehyde (UF) microcapsules yields up to 127% increase in fracture toughness and induces a change in the fracture plane morphology to hackle markings. The fracture toughness of epoxy with embedded microcapsules is much greater than epoxy samples with similar concentrations of silica microspheres or solid UF polymer particles. The increased toughening associated with fluid-filled microcapsules is attributed to increased hackle markings as well as subsurface microcracking not observed for solid particle fillers. Overall the embedded microcapsules provide two independent effects: the increase in virgin fracture toughness from general toughening and the ability to self-heal the virgin fracture event.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Successful arrest and retardation of fatigue cracks is achieved with an in situ self-healing epoxy matrix composite that incorporates microencapsulated dicyclopentadiene (DCPD) healing agent and ...Grubbs’ first generation Ru catalyst. Healing agent is released into the crack plane by the propagating crack, where it polymerizes to form a polymer wedge, generating a crack tip shielding mechanism. Due to the complex kinetics of healing a growing crack, the resulting in situ retardation and arrest of fatigue cracks exhibit a strong dependence on the applied range of cyclic stress intensity Δ
K
I. Significant crack arrest and life-extension result when the in situ healing rate is faster than the crack growth rate. In loading cases where the crack grows too rapidly (maximum applied stress intensity factor is a significant percentage of the mode-I fracture toughness value), a carefully timed rest period can be used to prolong fatigue life up to 118%. At moderate Δ
K
I, in situ healing extends fatigue life by as much as 213%. Further improvements in fatigue life-extension are achieved by employing a rest period, which leads to permanent arrest at this moderate Δ
K
I. At lower values of applied stress intensity factor, self-healing yields complete arrest of fatigue cracks providing infinite fatigue life-extension.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Microspheres of wax containing embedded Grubbs' catalyst are generated by congealing a molten aqueous suspension. Even with a ten‐fold reduction in catalyst concentration from previous systems, these ...microspheres produce unprecedented levels of toughness recovery in a polymeric self‐healing material (see Figure). Unlike the previously reported systems, samples healed with the wax microspheres show nonlinear fracture behavior. A protocol that addresses this nonlinearity is employed to measure healing efficiency.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The addition of liquid-filled urea-formaldehyde (UF) microcapsules to an epoxy matrix leads to significant reduction in fatigue crack growth rate and corresponding increase in fatigue life. Mode-I ...fatigue crack propagation is measured using a tapered double-cantilever beam (TDCB) specimen for a range of microcapsule concentrations and sizes: 0, 5, 10, and 20% by weight and 50, 180, and 460 μm diameter. Cyclic crack growth in both the neat epoxy and epoxy filled with microcapsules obeys the Paris power law. Above a transition value of the applied stress intensity factor ΔKT, which corresponds to loading conditions where the size of the plastic zone approaches the size of the embedded microcapsules, the Paris law exponent decreases with increasing content of microcapsules, ranging from 9.7 for neat epoxy to approximately 4.5 for concentrations above 10 wt% microcapsules. Improved resistance to fatigue crack propagation, indicated by both the decreased crack growth rates and increased cyclic stress intensity for the onset of unstable fatigue-crack growth, is attributed to toughening mechanisms induced by the embedded microcapsules as well as crack shielding due to the release of fluid as the capsules are ruptured. In addition to increasing the inherent fatigue life of epoxy, embedded microcapsules filled with an appropriate healing agent provide a potential mechanism for self-healing of fatigue damage.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical ...degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background
The WHO Surgical Safety Checklist improves surgical outcomes, but evidence and theoretical frameworks for successful implementation in low‐income countries remain lacking. Based on ...previous research in Madagascar, a nationwide checklist implementation in Benin was designed and evaluated longitudinally.
Methods
This study had a longitudinal embedded mixed‐methods design. The well validated Consolidated Framework for Implementation Research (CFIR) was used to structure the approach and evaluate the implementation. Thirty‐six hospitals received 3‐day multidisciplinary training and 4‐month follow‐up. Seventeen hospitals were sampled purposively for evaluation at 12–18 months. The primary outcome was sustainability of checklist use at 12–18 months measured by questionnaire. Secondary outcomes were CFIR‐derived implementation outcomes, measured using the WHO Behaviourally Anchored Rating Scale (WHOBARS), safety questionnaires and focus groups.
Results
At 12–18 months, 86·0 per cent of participants (86 of 100) reported checklist use compared with 31·1 per cent (169 of 543) before training and 88·8 per cent (158 of 178) at 4 months. There was high‐fidelity use (median WHOBARS score 5·0 of 7; use of basic safety processes ranged from 85·0 to 99·0 per cent), and high penetration shown by a significant improvement in hospital safety culture (adapted Human Factors Attitude Questionnaire scores of 76·7, 81·1 and 82·2 per cent before, and at 4 and 12–18 months after training respectively; P < 0·001). Acceptability, adoption, appropriateness and feasibility scored 9·6–9·8 of 10. This approach incorporated 31 of 36 CFIR implementation constructs successfully.
Conclusion
This study shows successfully sustained nationwide checklist implementation using a validated implementation framework.
Implementation works
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
As a first step towards a new crack healing methodology for cyclic loading, this paper examines two promising crack-tip shielding mechanisms during fatigue of a microcapsule toughened epoxy. ...Artificial crack closure is achieved by injecting precatalyzed monomer into the crack plane to form a polymer wedge at the crack tip. The effect of wedge geometry is also considered, as dictated by crack loading conditions during infiltration. Crack-tip shielding by a polymer wedge formed with the crack held open under the maximum cyclic loading condition (
K
max) yields temporary crack arrest and extends the fatigue life by more than 20 times. Hydrodynamic pressure and viscous damping as a mechanism of crack-tip shielding are also investigated by injecting mineral oil into the crack plane. Viscous fluid flow leads to retardation of crack growth independent of initial loading conditions. The success of these mechanisms for retarding fatigue crack growth demonstrates the potential for in situ self-healing of fatigue damage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A search for mixing between active neutrinos and light sterile neutrinos has been performed by looking for muon neutrino disappearance in two detectors at baselines of 1.04 and 735 km, using a ...combined MINOS and MINOS+ exposure of 16.36×10^{20} protons on target. A simultaneous fit to the charged-current muon neutrino and neutral-current neutrino energy spectra in the two detectors yields no evidence for sterile neutrino mixing using a 3+1 model. The most stringent limit to date is set on the mixing parameter sin^{2}θ_{24} for most values of the sterile neutrino mass splitting Δm_{41}^{2}>10^{-4} eV^{2}.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Upper amphibolite facies felsic gneiss from Broken Hill records the metatexite to schlieren diatexite to massive diatexite transition in a single rock type over a scale of tens to hundreds of metres. ...The metatexites are characterized by centimetre‐scale segregation of melt into leucosomes to form stromatic migmatite. The schlieren diatexites are characterized by the disaggregation of the rocks and the development of schlieren migmatite. The massive diatexites represent a higher degree of disaggregation, lack schlieren and contain plagioclase and K‐feldspar phenocrysts. The transition from metatexite to schlieren diatexite and massive diatexite was heterogeneous with both disaggregation of the rock on a grain scale and disaggregation of the rock into centimetre‐ to metre‐scale rafts. As melt contents increased, the proportion of material disaggregated on a grain scale increased. The high proportion of melt needed to form diatexites at upper amphibolite facies conditions was the result of an influx of hydrous fluid at temperatures just above the solidus of the diatexites. Nearby metapelitic rocks, with a slightly higher solidus temperature, undergoing subsolidus muscovite breakdown are the likely source of the fluid. Continued heating during and after the influx of fluid led to melt contents of up to c. 60 mol.% in the massive diatexite. The metatexite zone probably involved little added fluid. Continued deformation during cooling and melt crystallization resulted in the extensive development of schlieren and late‐stage melt segregations and melt‐rich shear bands in the schlieren diatexite zone. The rocks of the massive diatexite zone lack these late‐stage segregations, consistent with the cessation of D2 deformation prior to them developing a crystal framework.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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