Key Engineering Materials Vols. 385-387

Abstract: In a companion paper in this conference [1] an experimental study is presented that deals with measuring fracture properties and obtaining 3D images of the particle structure in heterogeneous materials as mortars and concrete. The fracture mechanisms observed in the tests are modelled with a 3D lattice model. The heterogeneity of the model is directly implemented from the 3D images obtained in a CT-scanner. With this method realistic crack patterns can be obtained.

Abstract: In the adhesive postinstalled method, headed anchor is anchored into concrete by means of a high strength epoxy resin adhesive. To measure the concrete compressive strength, the metal anchor is “pulled” from the concrete. There occur four types of failure when the metal anchor is pulled out. This paper introduces the rationale of the adhesive postinstalled method to estimate the in-place concrete strength. The embedment depth and the diameter of the reaction ring are specified by experimental phenomenon and theoretical analysis.

Abstract: This paper deals with the transition from a localized damage state to crack formation. Several attempts have already been made in this field. Our approach is in the continuity of studies where thermodynamic considerations lead to the definition of an equivalent crack concept. The main idea consists in replacing a damaged localized zone by a crack in order to recover the same amount of dissipated energy. On the one hand, a nonlocal model is used to modelize accurately localized damage. On the other hand, an elastic model which authorizes the formation of a crack described by a cohesive zone model is used. This cohesive zone model is defined thermodynamically in order to be in concordance with the damage model. The method allows obtaining the cohesive zone model traction curve from the knowledge of the nonlocal damage model solution. The numerical implementation is done using a Lagrangian multiplier that ensures the energetic equivalence between both models.

Abstract: The present paper investigates specific sustained crushing stress (SSCS) of various composite laminate designs and stiffened boxes under axial crushing test. In this regard, an optimum composite crash box design is sought by studying the effect of laminate design and stiffeners on SSCS. Crash boxes were fabricated from carbon/epoxy twill-weave fabrics of [0]4, [45]4 and [0,45]2. The progressive failure with three distinct crushing modes of transverse shearing, lamina bending and brittle fracture was observed for three laminate designs. Two new assembled composite boxes were made from channels and V-shape stiffener and tested in quasi-static condition. Adhesive bonding was used in joining the channelled and stiffened boxes. Measured amount of SSCS for all models were compared to find an optimum crash box. It was found SSCS increases with increasing proportion of 0° plies in the laminate.

Abstract: Ti-51.45at.%Ni thin films were deposited onto copper substrates by magnetron sputtering. The copper substrates were pre-punched into dog-bone specimens with 4.5mm×30mm(gauge portion) ×35µm( thickness). The substrate temperature was about 673K. The thin films were about 20µm thick. The as-deposited films were first solution treated at 1073K for 1h, and then aged at 773K for 30min. The grain size was estimated to be 1.5µm from scanning electron microscopy micrographs. Tensile tests were carried out on CSS-44100 electron universal test-machine. The strain rate was 1.1×10-4 s-1. The stress-strain curves of the free-standing film were obtained from the experimental stress-strain curves of copper substrate together with the thin film adherent to the substrate compared with the curves of copper substrate without film. The Hall-Patch coefficient was calculated, k=205Mpa.µm1/2. It seems that the Hall-Patch coefficient decreases with increasing film thickness. The experimental results showed that a series of parallel cracks grew in a concerted fashion across the thin film and the cracks were equally spaced. The cracks were more closely spaced if the film stress was increased. The fracture toughness of the film was estimated, c KΙ =0.96MPa·m1/2. Therefore, the minimum crack spacing is predicted by the film stress given.

Abstract: Steel reinforced concrete (SRC) structure is a kind of building structure with excellent mechanical performance, but the theory of crack width is not very clear. In recent years, the fracture energy is more and more applied to research concrete materials, which has opened up a new field for concrete materials modeling. In this paper, crack width model for SRC structure based on fracture energy concept is put forward. A uniaxial tension model is employed in the analysis for simplification. On the ground of the stress equilibrium as well as the relation among relative slip, steel strain and concrete strain, the basic equations are derived. By introducing the interfacial nonlinear bond stress versus slip constitutive relation between embedded steel and concrete, the analytical solution for distribution of slip along the interface is obtained. And based on this result, the influence of the interfacial bond-slip on tension stiffening of the steel is considered. The displacements of steel and concrete at the crack face under different load levels are computed and analyzed respectively. Finally according to the principle of work and power as well as the fracture energy concept of plain concrete, expression for fracture energy of SRC structures is obtained, and the relation of crack width and concrete fracture energy is established. The comparison shows that the fracture energy based on the model agrees with the test results well.

Abstract: Based on tests under low cyclic reversed horizontal loading, damage behaviors of steel reinforced high strength and high performance concrete (SRHSHPC) frame columns are analyzed. The strength attenuation that considered as damage variable is figured out, and the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the strength attenuation is discussed. The accumulative damage model, which can reveal the effect of cyclic loading and maximum deformation, is established for the SRHSHPC frame columns. The different phases of damage growth and their features for the SRHSHPC frame columns are analyzed, and the relation of damage and displacement is ascertained. Furthermore, the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the damage development is also discussed. The results show that the damage model could give a rational description for damaging process of the SRHSHPC frame columns.

Abstract: A mechanical model of the visco-elastic compressible material is established in order to investigate the viscous effect in dynamic growing crack-tip field. The constitutive equations on the visco-elastic compressible material are deducted. Through asymptotic analysis, it is shown that in the stable creep growing stage, the elastic-deformation and the visco-deformation are equally dominant in the near-tip field, as 1 ( 1) n r− − . The asymptotic solutions of separative variable in the crack-tip field are aslo obtained. According to numerical calculation, the curves of stress, stain and displacement are given. The results indicate that the near-tip fields are mainly governed by the creep exponent n and Mach number M ; the stress fields of mode I and mode II is slightly affected by the elastic compressible deformation; the strain and displacement fields of mode I are deeply affected by the elastic compressible deformation. However, the strain and displacement fields of mode II are less affected by the elastic compressible deformation. The asymptotic solutions of dynamic growing crack-tip field gained here can conveniently degenerate the incompressible case, when the Poisson ratio 0.5 ν→ , named as HR field. The conclusions can provide the references for further studying the dynamic growing crack-tip field in compressible material.

Abstract: In mechanical engineering, circular hole is used widely in structure design. When the structure is overloaded or the load is changed regularly, cracks emerge and spread. Based on the former study of dynamic stress concentration problem of SH wave by a crack originating at a circular hole edge, in this paper, the method of Green’s function is used to investigate the problem of dynamic stress intensity problem of double linear cracks near a circular hole impacted by incident SH-wave. The train of thought for this problem is that: Firstly, a Green’s function is constructed for the problem, which is a fundamental solution of displacement field for an elastic space possessing a circular hole and a linear crack while bearing out-of-plane harmonic line source force at any point; Secondly, in terms of the solution of SH-wave’s scattering by an elastic space with a circular hole and a linear crack, anti-plane stresses which are the same in quantity but opposite in direction to those mentioned before, are loaded at the region where the second crack is in existent actually, we called this process “crack-division”; Finally, the expressions of the dynamic stress intensity factor(DSIF) of the cracks are given when the circular hole and double linear crack exist at the same time. Then, by using the expressions, an example was provided to show the effect of circular hole and cracks on the dynamic stress intensity factor of the cracks.

Abstract: An anti-fatigued criterion of annularly breached shaft on mechanical design has been put forward, and the main factors that affect fatigue life of shaft are discussed. The interrelation of the main factors and the framework is founded. A new assessment method to fatigue life of shaft has been put forward according to Corten-Dolan’s theory modified Miner's rule. The effect of supporting conditions to fatigue life of shaft is discussed and the influencing parameters are obtained. The results show that the fatigue life of broad support in two sides is longer than that of narrow support in two sides. The results will establish the base of anti-fatigue design of shaft.