An experimental investigation of dynamic crack propagation in a brittle material reinforced with a ductile layer

The fracture behavior of a dynamically loaded edge crack in a brittle-ductile layered material, as a function of applied loading rate, was experimentally investigated. Layered specimens were prepared by sandwiching a thin layer of ductile aluminum between two thick layers of brittle Homalite-100. The layers were bonded using Loctite Depend 330 adhesive, and a naturally sharp edge crack was introduced in one of the Homalite-100 layers. These single-edge notched specimens were loaded in dynamic three-point bending using a modified Hopkinson bar. The fracture process was imaged in real time using dynamic photoelasticity in conjunction with digital high-speed photography, and the applied load and load-point displacement histories were determined from the strain signals recorded at two locations on the Hopkinson bar. The results of this study indicated two distinct mechanisms of dynamic failure, depending on the applied loading rate. At lower loading rates, the starter crack arrested on reaching the aluminum layer and then caused delamination along the aluminum–Homalite interface. On the contrary, as the loading rate was increased, interfacial delamination was followed by crack re-initiation in the Homalite layer opposite to the initial starter crack. It was determined that the times required for crack initiation, delamination and crack re-initiation decreased as the loading rate was increased. However, it was also observed that the applied load values associated with each event increased with increasing loading rate. These observations indicate that both the dynamic failure process and plausibly the failure mode transition are affected by the rate-dependent properties of Homalite, aluminum and the interfacial bond. Finally, based on the measured peak loads and the observed failure mechanisms it was concluded that the incorporation of a thin ductile reinforcement layer can increase both the overall fracture toughness and strength of a nominally brittle material.     

Terfenol棒径向开缝数目的计算

本文给出了一种简便的计算方法，用以计算满足极限工作频率要求的切割份数，并附以算例，与实际相符合。     

Account of the Cross-Sectional Deplanation of a Composite Bar in Determining the Critical Force

A method for determining the critical force for an axially compressed composite bar with account of deplanation of its cross sections is considered. It is proposed to consider the cross-sectional deplanation, which decreases the critical force, by lowering the basic flexural stiffness of the bar by the value resulting from this effect. General relationships for calculating this value for composite bars are obtained. Numerical results are presented, which show the decrease in the critical force as a function of some parameters for transversely isotropic bars of rectangular cross section.     

巯基功能化金纳米搅拌棒的制备及其对Pb(Ⅱ)和Cd(Ⅱ)的吸附检测

为实现金纳米粒子(AuNPs)对环境水体中重金属离子的选择性吸附,以刻饰不锈钢丝为基体,采用化学沉积法在刻蚀不锈钢丝表面沉积AuNPs,再用自组装法将1,8-辛二硫醇修饰于AuNPs上,制备了一种以巯基功能化金纳米为吸附剂的金属搅拌棒(AuNPs-SH-SBSE)。采用电感耦合等离子发射光谱仪(ICPOES)为检测手段,以常见的金属离子Pb(Ⅱ)和Cd(Ⅱ)为例,评价了金属搅拌棒的萃取分离性能。考察了吸附时间、pH值、解吸溶剂等因素对Pb(Ⅱ)和Cd(Ⅱ)吸附率的影响。结果表明,当吸附平衡时间为30min、pH 8.0,6.0 mL 1.5 mol/L HNO_3作洗脱剂时,Pb(Ⅱ)和Cd(Ⅱ)的吸附率分别达98.5%和87.4%。将该方法用于实际样品中痕量Pb(Ⅱ)和Cd(Ⅱ)的吸附检测,其线性范围分别为0.1~50 mg/L和0.2~20 mg/L,方法的检出限(S/N=3)分别为24 ng/L和3.6μg/L。在低、高2个浓度水平下进行加标回收实验,回收率分别为85.4%~105.0%和74.2%~97.8%,相对标准偏差(RSD,n=3)分别为3.8%~8.2%和4.2%~10.6%。该方法简单、快速、灵敏,可应用于环境水体中Pb(Ⅱ)和Cd(Ⅱ)的分离检测。     

Identification of volatile markers for the detection of adulterants in red ginseng (Panax ginseng) juice using headspace stir‐bar sorptive extraction coupled with gas chromatography and mass spectrometry

Red ginseng (Panax ginseng) products are frequently adulterated by manufacturers with cheaper medicinal plant products including deodeok (Codonopsis lanceolata) and doraji (Platycodon grandiflorum) to increase profits. To identify possible volatile markers for the adulteration of red ginseng juices with deodeok or doraji, a headspace stir‐bar sorptive extraction method was developed. Gas chromatography with mass spectrometry and untargeted metabolomics analysis revealed that 1‐hexanol, cis‐3‐hexen‐1‐ol, and trans‐2‐hexen‐1‐ol are abundantly present in deodeok and doraji but not red ginseng. The peak area ratios in gas chromatograms of these compounds in red ginseng juices mixed with deodeok or doraji indicate that these volatile chemicals can be used as markers to detect the adulteration of red ginseng juice.     

Determination of Aromatic Hydrocarbons,Phenols, and Polycyclic Aromatic Hydrocarbons in Water by Stir bar Sorptive Extraction and Gas Chromatography–Mass Spectrometry

The paper presents procedures for stir bar sorptive extraction for selected priority substances that include polycyclic aromatic hydrocarbons, phenols, and benzene and its aromatic homologs. Three extraction and instrumental analysis procedures were developed for the determination of 16 compounds. The developed solid-phase extraction methods using a movable element had high recoveries above 70%. Extraction methods were optimized by selecting an appropriate time and temperature of the process, the sample pH, and stirring speed. The detection limits for the polycyclic aromatic hydrocarbons ranged from 0.33?µg/dm³ for naphthalene to 2.22?µg/dm³ for phenanthrene. Slightly higher limits of quantification were obtained for phenols: from 9.21?µg/dm³ for phenol to 0.51?µg/dm³ for 2,4,6-trimethylphenol. The highest limit of quantification for the tested compounds was obtained for benzene, with a value of 36.6?µg/dm³, while for toluene and ethylbenzene, the values did not exceed 2.7?µg/dm³.     

Polydimethylsiloxane rod extraction, a novel technique for the determination of organic micropollutants in water samples by thermal desorption-capillary gas chromatography-mass spectrometry

A novel, simple and inexpensive approach to absorptive extraction of organic compounds from environmental samples is presented. It consists of a polydimethylsiloxane rod used as an extraction media, enriched with analytes during shaking, then thermally desorbed and analyzed by GC-MS. Its performance was illustrated and evaluated for the enrichment of sub- to ng/l of selected chlorinated compounds (chlorobenzenes and polychlorinated biphenyls) in water samples. The new approach was compared to the stir bar sorptive extraction performance. A natural ground water sample from Bitterfeld, Germany, was also extracted using both methods, showing good agreement. The proposed approach presented good linearity, high sensitivity, good blank levels and recoveries comparable to stir bars, together with advantages such as simplicity, lower cost and higher feasibility.     

Impact of water/PDMS phase ratio,volume of PDMS,and sampling time on Stir Bar Sorptive Extraction (SBSE) recovery of some pesticides with different KO/W

In Stir Bar Sorptive Extraction (SBSE) organic analytes are enriched from aqueous samples by sorption onto a thick film of polydimethylsiloxane (PDMS) coated on a glass‐enveloped magnet. Sampled analytes are recovered by thermodesorption (TDS) and analysed on‐line by cGC‐MS. This study evaluates the SBSE recovery as a function of K_O/W, the phase ratio (β), PDMS volume (20, 40, and 110 μL), sample volumes (4, 10, 100, and 1000 mL), and sampling time (0.67, 1, 2, 4, 5, 6, and 24 h) for three pesticides with different K_O/W [parathion methyl (K_O/W: 7.24×10²), β‐endosulfan (K_O/W: 6.8×10³), and buprofezin (K_O/W: 2.0×10⁴)]. Experimental recoveries with SBSE in reasonable sampling times were found to be mainly conditioned by β, which must be as low as possible either by operating on small sample volumes or by using stir bars coated with high PDMS volume when samples of relatively large volume are analysed.     

Validation of stir bar sorptive extraction for the determination of 24 priority substances from the European Water Framework Directive in estuarine and sea water

This paper describes the validation of a method for the determination of 24 priority substances from the European Framework Directive in estuarine and sea water using the new extraction technique known as stir bar sorptive extraction (SBSE), followed by thermal desorption using capillary gas chromatography-mass spectrometry. We studied linearity, detection and quantitation limits and accuracy (which includes determination of trueness and precision). Using the lack-of-fit method we tested linearity in the 0-200 ng L⁻¹ range for all the priority substances. The detection and quantification limits were less than 5 and 10 ng L⁻¹, respectively, for most of the compounds studied. Precision was assessed by variance analysis (ANOVA) and relative standard values of less than 10% were obtained for repeatability and less than 15% for intermediate precision. The recovery percentages in spiked estuarine and sea water were close to 100%. Finally, for quality control of the method (stability of precision and accuracy through time), we developed a method for calculating Shewhart control charts based on the information obtained in the validation process.     

Solvent bar microextraction combined with high‐performance liquid chromatography for preconcentration and determination of pramipexole in biological samples

A simple, rapid and sensitive analytical method for preconcentration and determination of pramipexole in different biological samples has been developed using solvent bar microextraction (SBME) combined with HPLC‐UV. The target drugs were extracted from 10 mL of basic aqueous sample solution into an organic extracting solvent located inside the pores of a polypropylene hollow fiber, then back‐extracted into an acidified aqueous solution in the lumen of the hollow fiber. In order to obtain high extraction efficiency, the effect of different variables on the extraction efficiency was studied simultaneously using an experimental design. The experimental parameters of SBME were optimized using a Box–Behnken design after a Plackett–Burman screening design. Under the optimized conditions, an enrichment factor up to 96 was achieved and the relative standard deviation of the method was 4.64% (n = 5). The linear range was 0.05–2000 µg/L with a correlation coefficient (r) of 0.987. Finally, the applicability of the proposed method was evaluated by extraction and determination of pramipexole in plasma and urine samples. The results indicated that SBME method has excellent clean‐up and high preconcentration factor and can serve as a simple and sensitive method for analysis of pramipexole in biological samples. Copyright © 2013 John Wiley & Sons, Ltd.