161 research outputs found
Comparative experimental study of dynamic compressive strength of mortar with glass and basalt fibres
No full textSpecimen reinforced with glass and basalt fibers were prepared using Standard Portland cement (CEM I, 52.5 R as prescribed by EN 197-1) and standard sand, in accordance with EN 196-1. From this cementitious mixture, a reference cement mortar without fibers was first prepared. Compressive strength, modulus of elasticity, and mod of fracture were determined for all specimens. Static and dynamic properties were investigated using Instron testing machine and split Hopkinson pressure bar, respectively. Content of the glass fibers in the mortar does not influence the fracture stress at static loading conditions in a clearly observed way. Moreover at dynamic range 5% content of the fiber results in a significant drop of fracture stress. Analysis of the basalt fibers influence on the fracture stress shows that optimal content of this reinforcement is equal to 3% for both static and dynamic loading conditions. Further increase of the fiber share gives the opposite effect, i.e. drop of the fracture stress
Dynamic behaviour of HPFRCC: The influence of fibres dispersion
No full textThe promise of fibre-reinforced cementitious composites for dynamic loading application stems from their observed
good response under static loading mainly due to fibre contribution. An experimental research aimed at contributing to the
understanding of the behaviour of advanced fibre-reinforced cementitious composites subjected to low and high strain rates
was carried out underlining the influence of fibres. The material behaviour was investigated at three strain rates (0.1, 1, and
150 s−1) and the tests results were compared with their static behaviour. Tests at intermediate strain rates (0.1–1 s
−1) were carried out by means of a hydro-pneumatic machine (HPM), while high strain rates (150 s−1) were investigated by exploiting a
modified Hopkinson bar (MHB). Particular attention has been placed on the influence of fibre and fibre dispersion on the dynamic
behaviour of the materials: matrix, HPFRCC with random fibre distribution and aligned fibres were compared. The comparison
between static and dynamic tests highlighted several relevant aspects regarding the influence of fibres on the peak strength and
post-peak behaviour at high strain rate
Energy absorption at high strain rate of glass fiber reinforced mortars
No full textIn this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass fibers affected energy absorption and tensile strength at high strain-rate of the fiber reinforced mortar. The Dynamic Increase Factor (DIF) was finally evaluated
Strain rate effects on reinforcing steels in tension
No full textIt is unquestionable the fact that a structural system should be able to fulfil the function for which it was created, without being damaged to an extent disproportionate to the cause of damage. In addition, it is an undeniable fact that in reinforced concrete structures under severe dynamic loadings, both concrete and reinforcing bars are subjected to high strain-rates. Although the behavior of the reinforcing steel under high strain rates is of capital importance in the structural assessment under the abovementioned conditions, only the behaviour of concrete has been widely studied. Due to this lack of data on the reinforcing steel under high strain rates, an experimental program on rebar reinforcing steels under high strain rates in tension is running at the DynaMat Laboratory. In this paper a comparison of the behaviour in a wide range of strain-rates of several types of reinforcing steel in tension is presented. Three reinforcing steels, commonly proposed by the European Standards, are compared: B500A, B500B and B500C. Lastly, an evaluation of the most common constitutive laws is performed
Relaxation model for dynamic plastic deformation of materials
No full textMechanical model for plastic relaxation of stresses in metals has been proposed. Our approach based on a characteristic plastic relaxation time, which is assumed as a material parameter. In a number of tasks values of its parameter become similarly high and it leads to dynamic effect appearing even at low strain rates deformation condition. The phenomenon of yield drop is one of these manifestations. We also discuss a physically based assumption (in the frames of dislocation theory) for analytical form of relaxation time. We find that there are two different characteristic relaxation time parameters, which is playing a main role for different stages of plastic deformation in low defect crystals.</p
Dynamic behaviour of cement mortars reinforced with glass and basalt fibres
No full textIn this paper, the dynamic behaviour of cement mortars reinforced with both glass and basalt fibres is studied. The influence of the addition of both types of fibre on energy absorption and tensile strength at high strain-rate was investigated, and the performance of the two types of fibre-reinforced mortar was compared. For this aim, basalt and glass fibres with same diameter and length were used. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass and basalt fibres affected energy absorption and tensile strength of the fibre reinforced mortar at high strain-rate. The Dynamic Increase Factor (DIF) was finally evaluated. The experimental results show that DIF is not significantly affected by the addition of basalt and glass fibres, while energy absorption at high strain rate is significantly increased by the addition of glass fibres and only slightly increased by the addition of basalt fibres
Dynamic tensile behaviour of high performance fibre reinforced cementitious composites after high temperature exposure
No full textThe uniaxial tension behaviour of high performance cementitious composites subjected to
high strain rates after high temperature exposure has never been investigated. The material
investigated was a steel fibre reinforced mortar. Straight low carbon steel micro-fibres
were used. The fibre content was 1.25% by volume and the mix design guaranteed a self
compacting mixture. The main purpose of the research was to highlight the role of thermal
damage in uniaxial tension at low and high strain rate loadings. Looking in particular at
peak strength and post-peak toughness the results show that, in low strain rate tests after
high temperature exposure up to 600 C, the thermal damage progressively reduces the
toughness and weakly increases the strength; at high strain rate the peak strength significantly
increases in comparison with low strain rate one for all the temperature investigated,
while the toughness for growing temperature progressively decreases
Mechanical properties of s355 under extreme coupled effect of high temperatures and high strain rates
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