High strain rate visco-damageable behavior of Advanced Sheet Molding Compound (A-SMC) under tension

Advanced Sheet Molding Compound (A-SMC) is a serious composite material candidate for structural automotive parts. It has a thermoset matrix and consists of high weight content of glass fibers (50% in mass) compared to standard SMC with less than 30% weight fiber content. During crash events, structural parts are heavily exposed to high rates of loading and straining. This work is concerned with the development of an advanced experimental approach devoted to the micro and macroscopic characterization of A-SMC mechanical behavior under high-speed tension. High speed tensile tests are achieved using servo-hydraulic test equipment in order to get required high strain rates up to 100 s⁻¹. Local deformation is measured through a contactless technique using a high speed camera. Numerical computations have led to an optimal design of the specimen geometry and the experimental damping systems have been optimized in terms of thickness and material properties. These simulations were achieved using ABAQUS explicit finite element code. The developed experimental methodology is applied for two types of A-SMC: Randomly Oriented (RO) and Highly Oriented (HO) plates. In the case of HO samples, two tensile directions were chosen: HO-0° (parallel to the Mold Flow Direction (MFD)) and HO-90° (perpendicular to the MFD). High speed tensile tests results show that A-SMC behavior is strongly strain-rate dependent although the Young's modulus remains constant with increasing strain rate. In the case of HO-0°, the stress damage threshold is shown an increase of 63%, when the strain rate varies from quasi-static (0.001 s⁻¹) to 100 s⁻¹. The experimental methodology was coupled to microscopic observations using SEM. Damage mechanisms investigation of HO and RO specimens showed a competition between two mechanisms: fiber-matrix interface debonding and pseudo-delamination between neighboring bundles of fibers. It is shown that pseudo-delamination cannot be neglected. In fact, this mechanism can greatly participate to energy absorption during crash. Moreover, the influence of fiber orientation and imposed velocity is studied. It is shown that high strain rate and oriented fiber in the tensile direction favor the pseudo-delamination.     

Development of Cu particles and Cu core-shell particles reinforced Al composite

Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cu_p composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable.     

Mechanical damage characterization of glass fiber-reinforced polymer laminates by ultrasonic maps

A method for simultaneous measurement of the thickness and density for Glass Fiber-Reinforced Polymer (GFRP) laminate plates with ultrasonic waves in C-Scan mode is presented in the form of maps. The method uses three different signals in immersion pulse-echo C-Scan mode. The maps obtained based on the density show the heterogeneity of the material at high resolution at the pixel level (1 × 1 mm²) and therefore they represent an efficient tool to assess and evaluate the damage of the composite structures after manufacturing and after an applied mechanical loading.     

Recovery of residual nutrients from agri-food byproducts using a combination of solid-state fermentation and insect rearing

The present research develops an innovative nutrient recovery strategy for capturing of un-utilised nutrients from agri-food byproducts using a combination of solid state fermentation (SSF) and insect rearing. SSF of borage and flaxseed meals were performed using GRAS organisms to release indigenous nutrients and to produce additional nutrients. Proximate analysis of the SSF-meals showed increases in both lipid and protein contents. Black soldier fly larvae (BSFL) were then grown on these SSF-meals for 12 day. The meals fermented singularly with Lactobacillus plantarum or Aspergillus niger displayed up to 30% enhancement in BSFL biomass, and dual fermentation with L. plantarum and Aspergillus oryzae resulted in an additional 10% enhancement. These examinations showed SFL use over-90% of proteins and lipids in SSF-meals. The results indicate that fermentation of these low-value meals can boost the efficacy of larval growth and the recovery of nutrients from agricultural byproducts as larval biomass.     

The effects of surface-modified graphene nanoplatelets on the sliding wear properties of basalt fibers-reinforced epoxy composites

Possessing unique designs and properties absent in conventional materials, nanocomposites have made a remarkable imprint in science and technology. This is particularly true regarding the polymer matrix composites when they are further reinforced with nanoparticles. In this study, the effects of different weight percentages (0, 0.1, 0.2, 0.3, 0.4, and 0.5) of surface-modified graphene nanoplatelets (GNPs) on the microhardness and wear properties of basalt fibers/epoxy composites were investigated. The GNPs were surface modified by silane, and the composites were made by the hand lay-up method. The wear tests were conducted under two different loads of 20 and 40 N. The best wear properties were achieved at 0.3 wt % GNPs as a result of the GNPs' self-lubrication property and the formation of a stable transfer/lubricating film at the pin and disk interface. Moreover, the friction coefficient was lower at the higher normal load of 40 N. The microscopic studies by FESEM and SEM showed that the presence of GNPs up to 0.3 wt % led to the stability of the transfer/lubricating film by enhancing the adhesion of the basalt fibers to the epoxy resin. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47986.     

Core–shell NTC materials with low thermal constant and high resistivity for wide-temperature thermistor ceramics

Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al₂O₃-modified Co_1.5Mn_1.2Ni_0.3O₄ NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co_1.5Mn_1.2Ni_0.3O₄ powder was coated with a thin Al₂O₃ shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al₂O₃ layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ ceramic with 0.08 wt% Al₂O₃ showed the increase of ρ double, and the change in its B was less than 140 K. The Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co_1.5Mn_1.2Ni_0.3O₄@Al₂O₃ NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics.     

Functional chemical modification of a porcine acellular dermal matrix with a modified naturally derived polysaccharide crosslinker

Antibacterial and physicochemical properties are generally considered important features of the porcine acellular dermal matrix (pADM). Oxidized 2-hydroxypropyltrimethyl ammonium chloride chitosan (OHTCC) was applied to crosslink with pADM at dosages of 1, 2, 4, 8, and 16%. The properties of the crosslinked pADM (OHTCC-pADM) were evaluated. DSC and TG analysis suggested that crosslinking could promote the thermal stability, the highest T_d, and T_max of OHTCC-pADM (8%) was 80 °C and 325 °C, which has been improved by 15 °C and 13 °C, respectively. While FTIR and AFM tests indicated that the structure integrity of collagen could still be maintained. SEM tests demonstrated the sustained three-dimensional architecture of OHTCC-pADM with appropriate porosity. Moreover, OHTCC-pADM exhibited improved ability to resist collagenase degradation, the degradation rate of 4%-, 8%-OHTCC-pADM was <50%. The tensile strength of OHTCC-pADM proved to be superior compared to pADM. Furthermore, 8%-OHTCC-pADM exhibited nearly 90% antibacterial activity against Escherichia coli, and Staphylococcus aureus. In addition, the results of the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazoliumbromide study showed that the cytocompatibility of OHTCC-pADM decreased with the increasing the amount of OHTCC, but all relative proliferation rates were above 80%. In conclusion, our study revealed that OHTCC stabilized and functionalized pADM while preserving good cytocompatibility. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47633.     

基于LBSN动态异构网络的时间感知兴趣点推荐

随着基于位置社交网络(Location-Based Social Network,LBSN)的快速发展,兴趣点(Point-Of-Interest,POI)推荐可以帮助人们发现有趣的并吸引人的位置。针对签到数据的稀疏性和用户兴趣的动态性等挑战性问题,提出了基于LBSN动态异构网络的时间感知兴趣点推荐算法。在LBSN异构网络模式中增加会话节点类型。通过动态元路径,在用户和兴趣点语义关系之间有效地融入时间信息、位置信息和社交信息等。设置了用户-兴趣点之间的动态元路径集,并提出了动态路径实例的偏好度计算方法。采用矩阵分解模型对不同动态偏好矩阵进行矩阵分解。根据不同动态元路径的用户特征矩阵和兴趣点特征矩阵,获取用户在目标时间访问兴趣点的推荐列表。实验结果表明,与其他兴趣点推荐方法相比,所提方法在兴趣点推荐精确度上取得了较好的推荐结果,具有良好的应用前景。     

Incomplete analytic hierarchy process with minimum weighted ordinal violations

ABSTRACT

Incomplete pairwise comparison matrices offer a natural way of expressing preferences in decision-making processes. Although ordinal information is crucial, there is a bias in the literature: cardinal models dominate. Ordinal models usually yield nonunique solutions; therefore, an approach blending ordinal and cardinal information is needed. In this work, we consider two cascading problems: first, we compute ordinal preferences, maximizing an index that combines ordinal and cardinal information; then, we obtain a cardinal ranking by enforcing ordinal constraints. Notably, we provide a sufficient condition (that is likely to be satisfied in practical cases) for the first problem to admit a unique solution and we develop a provably polynomial-time algorithm to compute it. The effectiveness of the proposed method is analyzed and compared with respect to other approaches and criteria at the state of the art.