Strain rate effect on the mechanical behaviour of a textile reinforced cement composite

The static tensile behaviour of Textile Reinforced Cement Composites is known and can be modeled adequately. However, using these static material properties under dynamic loadings such as impact and seismic loadings, can cause over- or underestimation of the material due to effects of strain rate. This work focuses on the strain rate dependency of a specific textile reinforced cement composite under tensile loadings at strain rates equivalent to quasi static applications towards low velocity impacts. It was found that the main damage mechanisms of this material stay the same. However cracking of the cement matrix is delayed to higher stress levels

Comparison between homogeneous and heterogeneous field information for plastic material identification

peer reviewedThe accuracy of a Finite Element Simulation for plastic deformation strongly depends on the chosen constitutive laws and the value of the material parameters within these laws. The identification of those mechanical parameters can be done based on homogeneous stress and strain fields such as those obtained in uniaxial tensile tests and simple shear tests performed in different plane material directions. Another way to identify plastic material parameters is by inverse modeling of an experiment exhibiting a heterogeneous stress and strain field. Experimental forces and strains are in this case compared to the simulated ones and it is tried to reduce the difference in a least-squares sense by optimizing the model parameters. The optimization technique used is this case is gradient based, which means that at every iteration a sensitivity calculation has to be performed in order to indicate the direction in which the parameters are to be identified. The basic principle of the inverse modeling procedure as it is used for parameter identification is the generation of a complex and heterogeneous deformation field that contains as much information as possible about the parameters to be identified. One way of obtaining such a non-homogeneous deformation is by altering the geometry of the specimen for a uniaxial test. Another possibility is to make the loading conditions more complex. In this paper both options are actually combined by using a biaxial tensile test on a perforated cruciform specimen. In the present paper, the work hardening of the material is assumed to be isotropic and it is described by a Swift law. The yield locus is modeled by the anisotropic Hill48 criterion. A comparison is made between the identification of the Hill48 parameters based on the one hand on the Lankford coefficients [1] and on the inverse modeling of a biaxial tensile test on the other han

Numerical modelling of the debonding between CFRP strips and concrete in shear tests under static loads using different approaches

The present paper deals with the finite element (FE) analysis of bond slip between concrete and carbon fiber reinforced polymer (CFRP) strips in a single pull-out test under static loads. The commercial software LS-DYNA is used to simulate the test set-up using a plastic damage material model and an elastic material model for the concrete prism and the unidirectional CFRP strip, respectively. The bond interface between the concrete and the CFRP strip is simulated following three different approaches using a perfect bond model, a cohesive bond model and contact algorithms based on recently developed proposed bond slip models. The numerical model is validated based on experimental test results available from literature. The debonding failure mode and the delamination loads of the CFRP strip are predicted. The numerical results show a good agreement with the experimental data using the cohesive bond model. The perfect bond model gives an overestimation of the delamination loads and of the damage distribution in the concrete prism

Non-Destructive Testing Techniques for Corrosion Assessment in Reinforced Concrete Structures in Kenya

Deterioration of concrete structures is inevitable due to the fact that it is subjected to deterring environmental factors. Therefore, inspection and maintenance of these structures should be done to ensure their serviceability. Many concrete structures have been constructed in Kenya. A survey of some of the existing multi-storey buildings shows that even some of the old ones are in good condition; examples are the Norfork Hotel, Sarova Stanley Hotel and the railway bridges built in early 1900s. Yet, ageing structures require periodic monitoring to check their serviceability. Currently, inspection of most structures is done solely by simple visual means which is not always adequate. In order to enhance reliable assessment of structures, the present research introduces non-destructive testing (NDT) techniques for corrosion damage diagnosis in Kenyan concrete structures. Visual inspection is followed by half-cell potential measurements, carbonation tests and chloride tests. Laboratory analysis as well as field testing shows that NDT techniques provide safe, fast and reliable tools for the assessment of structural integrity. Keywords: Reinforced Concrete, Deterioration, Inspection, Non-destructive testin

Direct evidence for stability of tetrahedral interstitial Er in Si up to 900∘^{\circ}C

Conversion electron emission channeling from the isotope $^{167m}$Er (2.28 s), which is the decay product of radioactive $^{167}$Tm (9.25 d), offers a means of monitoring the lattice sites of Er in single crystals. We have used this method to determine the lattice location of $^{167m}$Er in Si directly following room temperature implantation of $^{167}$Tm, after subsequent annealing steps, and also in situ during annealing up to 900°C. Following the recovery of implantation damage around 600°C, about 90% of Er occupies near-tetrahedral interstitial sites in both FZ and CZ Si. While in FZ Si $^{167m}$Er was found to be stable on these sites even at 900°C, the tetrahedral Er fraction in CZ Si decreased considerably after annealing for 10 min at 800°C and above

Identification of the plastic behavior of aluminum plates under free air explosions using inverse methods and full-field measurements

AbstractThis article describes an inverse method for the identification of the plastic behavior of aluminum plates subjected to sudden blast loads. The method uses full-field optical measurements taken during the first milliseconds of a free air explosion and the finite element method for the numerical prediction of the blast response. The identification is based on a damped least-squares solution according to the Levenberg–Marquardt formulation. Three different rate-dependent plasticity models are examined. First, a combined model based on linear strain hardening and the strain rate term of the Cowper–Symonds model, secondly, the Johnson–Cook model and finally, a combined model based on a bi-exponential relation for the strain hardening term and the strain rate term of the Cowper–Symonds model. A validation of the method and its sensitivity to measurement uncertainties is first provided according to virtual measurements generated with the finite element method. Next, the plastic behavior of aluminum is identified using measurements from real free air explosions obtained from a controlled detonation of C4. The results show that inverse methods can be successfully applied for the identification of the plastic behavior of metals subjected to blast waves. In addition, the material parameters identified with inverse methods enable the numerical prediction of the material’s response with increased accuracy

Explicit and implicit determinants of fair-trade buying behavior

We examined the usefulness of an implicit attitude measure (IAT) to explain the weak attitude-behavior relationships often found in research about ethical consumer behavior. The results indicated that the IAT effects for buyers and non-buyers of Fair Trade products were significantly different, showing that the IAT can be used to differentiate between buyers and non-buyers. Further, the authors conclude that the IAT has unique predictive validity and that most importantly implicit attitudes need to be enhanced to raise ethical consumer behavior