Thermal expansion of a novel hybrid SiC foam–SiC particles–Al composites

A new type of hybrid SiC foam–SiC particles–Al composites (V_SiC = 53, 56.2 and 59.9%) to be used as an electronic packaging substrate material were fabricated by squeeze casting technique, and their thermal expansion behavior was evaluated. The coefficients of thermal expansion (CTEs) of the hybrid composites in the range of 20–100 °C were found to be between 6.6 and 7.7 ppm/°C. The measured CTEs are much lower than those of SiC particle-reinforced aluminum (SiC_p–Al) composites with the same content of SiC because of the characteristic interpenetrating structure of the hybrid composites. A material of such a low CTE is ideal for electronic packaging because of the low thermal mismatch (and therefore, low thermal stresses) between the electronic component and the substrate. To achieve similar CTEs in SiC_p–Al composites, the volume fraction of SiC would be much higher than that in the hybrid composites.     

Experimental studying of buckling of stringer cylindrical shells under axial compression

Results of tests on axial compression of small-sized quality steel cylinder shells strengthened by 24 and 36 longitudinal thin-walled stiffeners are presented. The shell length was varied. Shells both with inside and outside stiffening were tested at simply supported and clamped edges. The shell carrying capacity that was governed in the tests by overall buckling in the elastic range was compared with the estimated critical loads based on structural-orthotropic theory. The satisfactory quantitative correlation has been received only for the long simply supported shells with 36 inner stiffeners, which demonstrated insignificant effect of local undulation that preceded overall deflections. The experimental and the theoretical results differed significantly (twice as much) when the actual mechanism of lateral deflection caused by the intensive local undulation differed from the adopted model.     

Materials Design of Microstructure in Grain Boundary and Second Phase Particles

A concept of microstructure design for materials or materials microstructure engineering is proposed. The argument was suggested based on literature review and some our new research work on second phase strengthening mechanisms and mechanical property modeling of a particulate reinforced metal matrix composite. Due to development of computer technology, it is possible now for us to establish the relationship between microstructures and properties systematically and quantitatively by analytical and numerical modeling in the research scope of computerization materials. Discussions and examples on intellectual optimization of microstructure are presented on two aspects:grain boundary engineering and optimal geometry of particulate reinforcements in two-phase materials.     

Cost optimization of singly and doubly reinforced concrete beams with EC2-2001

A model for the optimal design of rectangular reinforced concrete sections is presented considering the stress–strain diagrams described in EC2-2001 and MC90. The following expressions are developed: economic bending moment; optimal area of steel and optimal steel ratio between upper and lower steel. All the expressions are in nondimensional form. The present model is applied to four different classes of concrete described in MC90. It is concluded that in nondimensional form the equations are nearly coincident for both singly and doubly reinforcement. It is also concluded that the ultimate strain for concrete in the compression zone, ε_cm, lies between the strain for peak stress ε_c1 and the ultimate strain ε_cu. This result is relevant once that the maximum moment is obtained for this value, and not the value ε_cu, as defined in EC2-2001. Cost optimization is implemented in the code and compared with other optimum models based on the ultimate design of ACI.     

Apatitic calcium phosphates used in compression: rationalization of the end-use properties

Different apatitic calcium phosphates used as direct compression excipients have been developed in the last years. The difficulty to obtain reproducible synthesis explains their approximative and irregular composition. TRI-TAB® commercial grade called anhydrous tricalcium phosphate is associated to a chemical formula corresponding to a mixture of tricalcium phosphate (Ca₃(PO₄)₂) and calcium hydroxide (Ca(OH)₂). The chemical analysis shows that it is hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂).

The purpose of this work is to rationalize the chemical and physical natures of apatitic calcium phosphates used in direct compression, and thus their technological properties. Apatitic calcium phosphates differing in their Ca/P molar ratio (from 1.500 i.e. tricalcium phosphate to 1.667 i.e. hydroxyapatite) have been synthesized and their compression properties have been analysed. The results have been compared to those of TRI-TAB®. They pointed out the importance of the chemical nature contribution. Tricalcium phosphate-based materials exhibited an excellent compactibility when not calcined. Uncalcined hydroxyapatite had similar properties than TRI-TAB®, that is intermediate. Calcined tricalcium phosphate and hydroxyapatite showed a low compaction ability. It appears that the perfect chemical and physical control of the material is important in particle design to rationalize and optimise the tablet formulation as well as the process.     

商品混凝土现浇板裂缝问题与对策的探讨

介绍了商品混凝土现浇板裂缝出现的主要问题，从原材料选用、优化混凝土配合比、严把生产过程等方面论述了解决问题的相应对策，从而提高结构安全性、耐久性和使用功能。     

关于箍筋的无支长度的分析

文章对《高层建筑混凝土结构技术规程》(JG J3-2002)中的一个有争议的条文(箍筋的无支长度不应大于300m m)进行了分析,并给出了一个较合理答案。     

新立城水库牛腿扇形筋补强工程介绍

新立城水库在牛腿扇形筋补强工程中，采用了在原混凝土中，通过锚固装置，配设φ60圆钢的新技术，弥补了原结构配筋不足，施工方法简单，效益显著。     

The effect of anchorage on the effectiveness of the shear reinforcement in the punching zone

All building codes require well anchored shear systems in the punching zone. The enforced experimental investigation of 10 symmetric punching tests with conventional stirrups and stirrups made of fabric reinforcement shows, that the effectiveness of the shear reinforcement depends on the quality of the anchorage. This result could be confirmed by tests from the literature too. In addition, the punching design approach of DIN 1045-1, 2001 [Tragwerke aus Beton, Stahlbeton und Spannbeton, Teil1: Bemessung und Konstruktion. Beuth Verlag, Juli 2001] is presented.