Experimental Investigation of Oblique Impact Behavior of Adhesively Bonded Composite Single-Lap Joints

Applied Composite Materials - Determining the impact behavior of adhesive joints allows the designing of high-strength joints. Therefore, the dynamic behavior of adhesive joints has recently become...     

Cytologic diagnosis and subtyping of rhabdomyosarcoma

Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder of urea synthesis. Among females who carry a mutant OTC allele, there is a wide range of phenotypic variability, ranging from apparent normality to a severe onset and the resulting profound neurologic impairment observed in hemizygous males. This study was designed to define the phenotypic variability of OTC deficiency in ostensibly healthy carrier females and to compare them to noncarrier females from their own and other families. One hundred seventy-five women from 89 families participated in this study. Each completed a mailed questionnaire, allopurinol testing, and fasting plasma amino acid determinations. OTC carrier status was determined by pedigree analysis, allopurinol test results, and/or DNA mutation analysis. Overall, 79 women were identified as carriers of a mutant OTC allele (60 proband mothers, 19 relatives), and 96 women (32 proband mothers, 64 female relatives) were determined to be noncarriers. Comparison of biochemical phenotypes indicated that carriers and noncarriers do not differ in daily urinary creatinine excretion, but that carriers excrete significantly less urea nitrogen and total nitrogen, reflecting their significantly lower historically reported daily protein intake. Carriers had significantly higher levels of fasting plasma glutamine and alanine, and significantly lower levels of citrulline and arginine compared with noncarriers. Carriers and noncarriers reported similar demographic characteristics, anthropometric measurements, level of education, and medical and pregnancy histories. There was no indication of increased incidence of migraine headaches among carriers. Thus, we found no evidence that asymptomatic adult female OTC heterozygotes are at increased risk for previously unidentified health problems apart from an unknown risk for hyperammonemic encephalopathy as occurred in 3 of the carriers in this study. Because these episodes appear to be related to physiologic stress (fracture, parturition), it would seem medically prudent for carriers to be aware of this risk.     

Use of mineral admixtures for enhanced resistance against sulfate attack

The effect of mineral admixtures such as nano silica, micro silica, fly ash and ground granulated blast furnace slag on the expansion of mortar bars caused by internal and external sulfate attack was investigated. According to data recorded through 12 months, all of the mineral additives, particularly slag, have significantly reduced the expansions caused by sulfate attack. It was shown that, the effectiveness of nano silica was also very significant. When used with sulfate contaminated sands, high sulfate resistant mixtures were produced with 4–6% nano silica replacement ratios. In the case of external sulfate attack, however, only 2% nano silica is most likely enough for keeping the expansions below 0.03% after 12 months.     

Influence of immediate post-therapy bone scintigraphy in the assessment of response to therapy in a case of nasopharyngeal carcinoma

We have conducted a retrospective study of deaths on a paediatric medical intensive care unit over a two-year period and reviewed similar series from outside the UK. There were 89 deaths out of 651 admission (13.7% mortality). In almost two-thirds of the cases death occurred with a decision to limit medical treatment or withdraw mechanical ventilation, implying that additional or further therapy was considered futile. We highlight this as a crucially important issue in the practice of intensive care. More comprehensive studies are needed to help clinicians derive consensus on what constitutes a futile intervention, and therefore when such an intervention should be withheld. This will help families and society better understand the limitations of intensive care.     

Mode I and mixed mode fracture studies in brittle materials using the Brazilian disc specimen

High Strength Cement Mortar (HSCM) with very fine sand exhibits a typical brittle behavior. In the present work, a linear elastic fracture mechanics based model is used for the fracture studies conducted on this material. The experimental testing program is based on the diametral compression test of disc specimens containing an internal slant crack. Under the Mode I loading condition, the test method which has been previously used is applied to determine the critical value of the stress intensity factor, K_IC, for HSCM. The same dise specimen is also tested under combined Mode I and Mode II loading conditions. By changing the notch orientation angle with respect to the loading direction, the mode of fracture is varied from pure Mode I to Mixed-Mode. Based on the Mixed-Mode fracture envelope, it is shown that the disc specimen which is currently used for several brittle materials provides a wide range of |K_II|/K₁ ratios. In pure Mode I loading case, after determining K_IC, it is possible to obtain the graph of normalized critical load versus normalized crack length. For the purpose of comparison, some available experimental data on Mode I and/or Mixed Mode fracture of some other brittle materials such as glass, sintered carbide, and polymethyl methacrylate (PMMA) were also evaluated. It can be concluded that there is a good fit between the experimental results and the theory.

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Résumé Les mortiers à très haute résistance (MTHR) préparés avec du sable très fin ont exhibité un comportement typiquement fragile. Dans cet article un modèle de rupture élastique linéaire est utilisé pour étudier la rupture de ces matériaux. L'étude expérimentale consistait des essait des consistait des essais de compression diamétrale sur des éprouvettes en forme de disques contenant une fissure inclinée. Les essais conformes au Mode I utilisés auparavant sont appliqués pour déterminer la valeur critique du facteur d'intensité de la contrainte K_IC du MTHR. Les mêmes éprouvettes ont été ensuite essayées sous charge combinée du Mode I et Mode II. En changeant l'angle d'orientation de l'entaille par rapport à la direction de la force appliquée, le mode de rupture a été modifié du Mode I au Mode-Mixte. En se servant de l'enveloppe du Mode-Mixte de rupture, utilisée actuellement on a montré que l'éprouvette disque pouvait fournir une large pour les rapports |K_II|/K₁. Au cas de chargement simple de Mode I, après avoir déterminé K_IC il était possible d'obtenir un graphique entre la charge critique et la longueur de la fissure normalisées. D'autres résultats expérimentaux obtenus sur d'autres matériaux fragiles comme verre, carbide synthérisé et méthacrylate de polymethyl (PMMA) sont aussi évalués afin de réaliser une comparaison. On peut conclure qu'il existe une bonne conformité entre les résultats expérimentaux et théoriques.

     

Effects of water–cement ratio and curing time on the critical pore width of hardened cement paste

Mercury intrusion porosimetry (MIP) test is one of the techniques that have been widely used for analyzing the pore size distribution of hardened cement paste (hcp) and also for the determination of the critical pore width. This study presents the test results of the MIP experiments obtained for three different hcp specimens with the water–cement ratios of 0.26, 0.34, and 0.42 which had been cured for 7, 28, and 365 days under water. Thus, the effects of water–cement ratio and curing time on the critical pore width of hcp were investigated. Test results have shown that, within the limits of the work, and in case of complete hydration, the critical pore width of the hcp seems to be independent of water–cement ratio and is of the order of 25 nm. This value can be considered as the critical pore width of the portland cement gel.     

Low-speed bending impact behavior of adhesively bonded single-lap joints

This study addresses the low-speed impact behavior of adhesively bonded single-lap joints. An explicit dynamic finite element analysis was conducted in order to determine the damage initiation and propagation in the adhesive layers of adhesive single-lap joints under a bending impact load. A cohesive zone model was implemented to predict probable failure initiation and propagation along adhesive–adherend interfaces whereas an elasto-plastic material model was used for the adhesive zone between upper and lower adhesive interfaces as well as the adherends. The effect of the plastic deformation ability of adherend material on the damage mechanism of the adhesive layer was also studied for two aluminum materials Al 2024-T3 and Al 5754-0 having different strength and plastic deformation ability. The effects of impact energy (3 and 11 J) and the overlap length (25 and 40 mm) were also investigated. The predicted contact force-time, contact force-central displacement variations, the damage initiation and propagation mechanism were verified with experimental ones. The SEM and macroscope photographs of the adhesive fracture surfaces were similar to those of the explicit dynamic finite element analysis.     

A recommended specification for heavy vehicle rear underrun guards

A large research program was carried out to evaluate the effectiveness of different heavy vehicle rear underrun guards. Based on the test results, a recommended underrun guard specification was developed to prevent passenger injuries in such accidents. Data obtained from a series of static and full-scale crash tests performed at the Transport Canada Research Center was used in the development of the specification. Four different underrun guard designs were used during the full-scale crash tests. Three different vehicle models representing sub-compact, compact vehicles and light trucks and vans traveling at 48, 56 and 65 km/h relative speeds were used to impact underrun guards head on. The first 10 of the crash tests guard was attached to a simulated trailer while the last one performed using an actual truck. The results obtained from these tests show that a guard built to the minimum requirements of U.S. FMVSS 223 may not be strong enough to prevent passenger compartment intrusion especially in compact and sub-compact automobiles. This paper documents the tests performed, the results obtained and their analyses, and conclusions derived from these analyses. A recommended specification is prepared on the minimum performance that should be required for an effective underrun guard.