The results of a theoretical and experimental research project on the use of an innovative technique for strengthening concrete
beams are presented. A spacer element is inserted between the tension side of a beam and the composite material to increase
its lever arm and to enhance the over all stiffness of the strengthened beam. The main aim of this exploratory project was
to increase the ultimate failure load of strengthened beam specimens, whilst guaranteeing acceptable over all deflections
at the serviceability limit states. This resulted into a significant reduction in the amount of FPR required and in a better
utilization of the materials employed. A preliminary theoretical study was carried out to investigate the effect of Young’s
modulus, failure strain, and thickness of the element to be used as a spacer in order to determine the best possible candidate
material. Three tests on 2.5-m-long beams were carried out, and different anchorage techniques were used to try and prevent
the debonding of the strengthening system. The results from this pilot study are very promising, as the strengthening system
ensures an adequate initial stiffness along with an improved ultimate flexural capacity.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 403–416, May–June, 2008. 相似文献
Nanocomposites of polymers and montmorillonite (MMT) represent a type of important hybrid material. However, unlike in some natural hybrid materials where much improved mechanical properties are achieved by an ordered assembly (layered, sheet-like or fibrous morphology) of complementary hard and soft components on nano- and microscopic scales, the exfoliated MMT nano-sheets are generally randomly dispersed in bulk polymeric matrices. In this paper we utilized a pressure-induced flow (PIF) field to orient MMT nano-sheets and generate stratified morphologies in polyamide 6 (PA6)/MMT nanocomposite bulk material. The toughness and tensile strength can be simultaneously increased. In particular, the impact strength increased up to 10 fold higher than the same material obtained by conventional processing methods. The mechanism for enhancement could be the confinement of crack propagations and the tortuous energy dissipating paths, which are attributed to the oriented MMT and the anisotropic hierarchical morphologies formed during PIF-processing. 相似文献
The interactions of moving twin boundaries with stacking fault tetrahedra (SFTs) have been studied by molecular dynamics. The results reveal a spectrum of processes occurring during these interactions. In general, they lead to damage of the parent SFT and formation of new defects in the twin lattice. The character of these defects depends on the nature of the twinning front, the size of the SFT and its orientation with respect to incoming dislocations. Typical structures that may be produced in the twin include product-SFTs, free vacancies, planar stacking faults bounded by partial dislocations, mutually linked stacking faults on non-coplanar {111}T planes, small {111}T tetrahedra and their partial forms. Dislocation mechanisms involved in the formation of these defects are being analyzed. 相似文献
It has been shown that aging of tetramethoxysilane (TMOS)-based alcogels in solutions of tetraethoxysilane (TEOS)/methanol (MeOH) provides new monomers to the alcogel and favorably increases the strength and stiffness of the alcogel and hence reduces the shrinkage during the subsequent drying. Load relaxation experiments have been performed to determine the shear modulus (G), Poisson's ratio (), and the permeability of wet gel rods as a function of aging time in the TEOS/MeOH solution. The modulus of rupture (MOR) and G have also been obtained from 3-point bending tests. Aging the gels in 70 vol% TEOS/MeOH causes an increase in G from 0.48 MPa to 1.8 MPa and 7.4 MPa after aging for 24 hours and 144 hours, respectively.It is shown that the drying stress is actually increased by the aging treatment, but the increase in strength of the gel is even greater; hence, strengthening of the alcogels dramatically reduces the probability of cracking during drying. Unaged gels with higher TMOS concentrations corresponding to the silica content of gels aged in TEOS solution, however, showed large shrinkage and severe cracking. 相似文献
It has long been recognized that a successful strategy for computational plasticity will have to bridge across the meso scale in which the interactions of high quantities of dislocations dominate. In this work, a new meso-scale scheme based on the full dynamics of dislocation-density functions is proposed. In this scheme, the evolution of the dislocation-density functions is derived from a coarse-graining procedure which clearly defines the relationship between the discrete-line and density representations of the dislocation microstructure. Full dynamics of the dislocation-density functions are considered based on an “all-dislocation” concept in which statistically stored dislocations are preserved and treated in the same way as geometrically necessary dislocations. Elastic interactions between dislocations in a 3D space are treated in accordance with Mura's formula for eigen stress. Dislocation generation is considered as a consequence of dislocations to maintain their connectivity, and a special scheme is devised for this purpose. The model is applied to simulate a number of intensive microstructures involving discrete dislocation events, including loop expansion and shrinkage under applied and self stress, dipole annihilation, and Orowan looping. The scheme can also handle high densities of dislocations present in extensive microstructures. 相似文献
This article reviews the available literature published to date on the reinforcement of metals with carbon-nanofillers (CNTs and graphene), and also offers a specific focus on issues related to the mechanical and tribological properties of nanocomposites. Carbon-nanofillers (later denoted by C-nanofillers) are known to have extraordinary mechanical properties and multifaceted characteristics and are ideal candidates for the reinforcement of metals for numerous applications. However, their incorporation for practical applications has been challenging researchers for decades. The most important issue is uniform dispersion due to sizeable surface differences between carbon-nanofillers and metals. Other concerns are structural integrity, wetting with metals, and interfacial connections. Nanocomposite applications can only be effective when these challenges are properly addressed and overcome.
Section 1 assesses the importance of C-nanofillers and expressly highlights current research efforts to optimize dispersion in different metals along with processing techniques in section 2. The authors give special attention on C-nanofillers reinforcement contribution to enhanced mechanical strength of metals presented in section 3. C-nanofillers dispersion evaluation tools are highlighted in section 4. Authors also focuses on C-nanofillers role and factors directly associated with metal nanocomposite strength, as reported in the literature. Particular consideration is also given to knowledge sharing of attendant strengthening mechanisms along with contribution reported for empirically derived models used to predict strength. Section 6 solely dedicated to the tribological aspects of C-nanofillers reinforced metallic nanocomposites. Lastly, future recommendations and works need attention is summarized. 相似文献