Effect of Surface Treatment on Joint Performance and Fracture Morphology in Adhesively Bonded Al-Si Coated Ultra-High Strength Steel

The Corporate average fuel economy (CAFE) standard set by the National Highway Traffic Safety Administration (NHTSA) has prompted automotive manufacturers to produce increasingly fuel efficient vehicles. Lightweighting of vehicle structures to reduce carbon dioxide emissions can be enabled by advanced materials such as hot stamped ultra-high strength steel (UHSS), but requires new joining solutions for integration in future multi-material structures. Structural adhesives enable multi-material joining, and have been used to enhance the joint performance for mono-material structures to achieve improved joint strength and stiffness. However, implementation of adhesive joining for hot stamped UHSS requires an appropriate surface treatment to maximize the joint strength and to address delamination of the brittle intermetallic coating formed on the steel during processing. The present study investigated adhesive joining (3MTM Impact Resistant Structural Adhesive 7333, 3MTM Canada Company) of a hot stamped UHSS (Usibor® 1500-AS, ArcelorMittal Dofasco) using three surface preparation techniques: degrease using acetone (ACE), grit-blast (GB) treatment, and adhesion promotor (AP) treatment following grit-blasting. Three hot stamping thermal treatments were considered with three quenching die temperatures: room temperature (RT), 400°C, and 700°C, which varied the yield strength of the steel, and created some differences in the morphology of the intermetallic coating. The overall work examined the surface treatments for adhesive joining of hot stamped UHSS, intermetallic coating delamination mechanism and the adhesive failure morphology under different adhesive joint configurations. Adhesively joined adherends were evaluated using the single-lap shear (SLS) test to investigate the nine material conditions (three surface treatments, three steel thermal processing treatments). The measured joint strength of the GB and AP conditions were 60% and 56%, respectively, higher than the baseline ACE treatment (p <.001). The higher strength achieved from the GB treatment was attributed to removal of the intermetallic coating. The ACE treatment did not remove the intermetallic coating and resulted in the lowest joint strength with the largest variability of the conditions tested, attributed to intermetallic coating delamination. The intermetallic coating morphology included microcracks and Kirkendall voids, which facilitated coating delamination. The intermetallic coating delamination was associated with a measured SLS joint rotation of 2.5°-2.8° for all three thermal treatments, while the measured joint strength decreased as the thermal treatment temperature increased (22 MPa to 14 MPa). This decrease in joint strength was attributed to the lower yield strength of the adherend material enabling the critical joint rotation to be achieved at a lower applied load. Plastic deformation in the SLS adherends was observed in the GB and AP treatments for the 400°C and 700°C thermal treatments. No plastic deformation was identified for the RT thermal treatment. The fracture surfaces from four types of adhesively bonded test specimens (Mode I opening, Mode II shear, Mixed-Mode at 45° (MM45), and SLS) comprising steel adherends without any surface coating were investigated using an optical digital microscope. Analysis of the fracture surfaces revealed qualitative differences in the morphology for different modes of loading. Shear hackles were observed for Mode II loading, while Mode I demonstrated facets on the fracture surface. The fracture surfaces were quantified using the arithmetic mean roughness (Ra). Mode I demonstrated the lowest roughness (50 µm) while Mode II had the highest Ra (103 µm), attributed in part to the shear hackles. The MM45 (80 µm) and SLS (73 µm) demonstrated intermediate roughness values, corresponding to mixed mode loading. Thus, it was found that qualitative and quantitative assessment of fracture surfaces could be associated with the mode of loading, and mode mixity. Ultra-high strength boron steel provides an important design option for vehicle structural engineers, with high strength achieved through thermal processing but resulting in a brittle intermetallic coating that present challenges for adhesive joining. The present study investigated adhesive joint strength for boron steel, and the corresponding intermetallic coating failure pathways and their effect on joint strength measured using a single-lap shear test. The importance of surface treatment to remove the intermetallic coating was critical to achieve high joint strength with low variability

Mode I Traction-Separation Measured Using Rigid Double Cantilever Beam Applied to Structural Adhesive

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Adhesion on 6 August 2018, available online: https://doi.org/10.1080/00218464.2018.1502666Adhesive joining facilitates the development of multi-material vehicle structures; however, widespread adoption requires material properties to characterize adhesive joints for implementation in finite element (FE) models. Specifically, modeling adhesive joints using the cohesive zone method requires measuring the Mode I traction-separation response, which currently requires multiple tests. To address this need, a new method to determine the Mode I response was developed using the Rigid Double Cantilever Beam (RDCB) test, where the steel adherend geometry was designed to ensure high stiffness compared to structural epoxy adhesives. The samples were tested in tension with displacements measured from high-resolution imaging of the test. A new analysis method was developed with resulting Mode I traction-separation response within the expected range for this structural adhesive. The analysis was verified using a FE model of the test and compared to Tapered Double Cantilever Beam test data. Importantly, the predicted force-displacement response from the FE model, using the measured traction-separation curve, compared well to the measured force-displacement data. The proposed RDCB test demonstrated the ability to determine the Mode I response of a toughened structural adhesive using a single test, the results of which can then be readily implemented into FE simulations

Role of the Diphosphine Chelate in Emissive, Charge-Neutral Iridium(III) Complexes

A class of neutral tris-bidentate Ir(III) metal complexes incorporating a diphosphine as a chelate is prepared and characterized here for the first time. Treatment of [Ir(dppb)(tht)Cl3] (1) with fppzH afforded the dichloride complexes, trans-(Cl,Cl)[Ir(dppb)(fppz)Cl2] (2) and cis-(Cl,Cl)[Ir(dppb)(fppz)Cl2] (3). The reaction of 3 with the dianionic chelate precursor bipzH2 or mepzH2, in DMF gave the complex [Ir(dppb)(fppz)(bipz)] (4) or [Ir(dppb)(fppz)(mepz)] (5), respectively. In contrast, a hydride complex [Ir(dppb)(fppz)(bipzH)H] (6) was isolated instead of 4 in protic solvent, namely: DGME. All complexes 2 - 6 are luminescent in powder forms and thin films where the dichlorides (2, 3) emit with maxima at 590-627 nm (orange) and quantum yields (Q.Y.s) up to 90% whereas the tris-bidentate (4, 5) and hydride (6) complexes emit at 455-458 nm (blue) with Q.Y.s up to 70%. Hybrid TD-DFT calculations showed considerable MLCT contribution to the orange-emitting 2 and 3 but substantial ligand-centered 3ππ* transition character in the blue-emitting 4 - 6. The dppb does not participate to these radiative transitions in 4 - 6, but it provides the rigidity and steric bulk needed to promote the luminescence by suppressing the self-quenching in the solid state. Fabrication of an OLED with dopant 5 gave a deep blue CIE chromaticity of (0.16, 0.15). Superior blue emitters, which are vital in OLED applications, may be found in other neutral Ir(III) complexes containing phosphine chelates

The Role of Pulmonary Veins in Cancer Progression from a Computed Tomography Viewpoint

Background. We studied the role of pulmonary veins in cancer progression using computed tomography (CT) scans. Methods. We obtained data from 260 patients with pulmonary vein obstruction syndrome (PVOS). We used CT scans to investigate pulmonary lesions in relation to pulmonary veins. We divided the lesions into central and peripheral lesions by their anatomical location: in the lung parenchymal tissue or pulmonary vein; in the superior or inferior pulmonary vein; and by unilateral or bilateral presence in the lungs. Results. Of the 260 PVOS patients, 226 (87%) had central lesions, 231 (89%) had peripheral lesions, and 190 (75%) had mixed central and peripheral lesions. Among the 226 central lesions, 93% had lesions within the superior pulmonary vein, either bilaterally or unilaterally. Among the 231 peripheral lesions, 65% involved bilateral lungs, 70% involved lesions within the inferior pulmonary veins, and 23% had obvious metastatic extensions into the left atrium. All patients exhibited nodules within their pulmonary veins. The predeath status included respiratory failure (40%) and loss of consciousness (60%). Conclusion. CT scans play an important role in following tumor progression within pulmonary veins. Besides respiratory distress, PVOS cancer cells entering centrally can result in cardiac and cerebral events and loss of consciousness or can metastasize peripherally from the pulmonary veins to the lungs

Ample Pairs

We show that the ample degree of a stable theory with trivial forking is preserved when we consider the corresponding theory of belles paires, if it exists. This result also applies to the theory of $H$-structures of a trivial theory of rank $1$.Comment: Research partially supported by the program MTM2014-59178-P. The second author conducted research with support of the programme ANR-13-BS01-0006 Valcomo. The third author would like to thank the European Research Council grant 33882

Mediating role of resilience in the relationships of physical activity and mindful self-awareness with peace of mind among college students

Abstract Peace of mind (PoM) is an index of mental health in Asian culture and emphasizes low arousal, happiness, harmony, and an internal state of peacefulness. While previous studies have found that mindful self-awareness can contribute to PoM, regular physical activity (PA) is also an important factor contributing to one’s PoM due to its function in promoting one's resilience. The study aims to investigate a hypothetical model that assumes PA is associated with resilience while controlling for mindful self-awareness, contributing to PoM. The PoM scale, Connor-Davidson Resilience Scale, Chinese translation of Mindful Attention Awareness Scale, and PA self-report questionnaire were used. A path analysis was applied to test the association between these variables and the mediating role of resilience. A total of 436 students from a university in Taiwan were recruited; the mean age was 20.87, with 46.3% female and 73.6% engaging in over 150 min/week of moderate PA. Gender and age negatively correlated with PA. After controlling for age and gender, there was no direct effect of physical activity on PoM; both mindful self-awareness and PA predict resilience, which in turn predicts PoM, suggesting that both cognitive (i.e., mindful self-awareness) and PA are important to cultivate resilience and thus PoM

Arrhythmia and other modifiable risk factors in incident dementia and MCI among elderly individuals with low educational levels in Taiwan

IntroductionThere is increasing evidence that arrhythmia is a risk factor for dementia; however, it appears that arrhythmia affects the cognitive function of individuals differentially across age groups, races, and educational levels. Demographic differences including educational level have also been found to moderate the effects of modifiable risk factors for cognitive decline.MethodsThis study recruited 1,361 individuals including a group of cognitively unimpaired (CU) individuals, a group of patients with mild cognitive impairment (MCI), and a group of patients with dementia with low education levels. The participants were evaluated in terms of modifiable risk factors for dementia, including arrhythmia and neuropsychiatric symptoms.ResultsCox proportional hazard regression models revealed that among older MCI patients (&gt;75 years), those with arrhythmia faced an elevated risk of dementia. Among younger MCI patients, those taking anti-hypertensive drugs faced a relatively low risk of dementia. Among younger MCI patients, male sex and higher educational level were associated with an elevated risk of dementia. Among CU individuals, those with coronary heart disease and taking anti-lipid compounds faced an elevated risk of MCI and those with symptoms of depression faced an elevated risk of dementia.DiscussionThe risk and protective factors mentioned above could potentially be used as markers in predicting the onset of dementia in clinical settings, especially for individuals with low educational levels