Comparative study of failure mechanisms in steel and concrete members strengthened with CFRP composites

Over the last decade advanced composite materials, like carbon fibre reinforced polymer (CFRP), have increasingly been used in civil engineering infrastructure. The benefits of advanced composites are rapidly becoming evident. This paper focuses on the comparative performance of steel and concrete members retrofitted by carbon fibre reinforced polymers. The objective of this work is a systematic assessment and evaluation of the performance of CFRP for both the concrete and steel members available in the technical literature. Existing empirical and analytical models were studied. Comparison is made with respect to failure mode, bond characteristics, fatigue behaviour, durability, corrosion, load carrying capacity and force transfer. It is concluded that empirical expressions for the concrete-CFRP composite are not readily suited for direct use in the steel-CFRP composite. This paper identifies some of the major issues that need further investigation.

Numerical investigation of deformation and failure mechanisms of osteopontin-hydroxyapatite interfaces and mineralized collagen fibril arrays

This thesis is a comprehensive study of deformation and failure mechanisms in bone at nano- and micro-scale levels. It explores the mechanical behaviour of osteopontin-hydroxyapatite interfaces and mineralized collagen fibril arrays, through atomistic molecular dynamics and finite element simulations. This thesis shows some main factors contributing to the excellent material properties of bone and provides some guidelines for development of new artificial biological materials and medical implants.

A finite element analysis of dynamic fracture initiation by ductile failure mechanisms in a 4340 steel

In some recent dropweight impact experiments [5] with pre-notched bend specimens of 4340 steel, it was observed that considerable crack tunneling occurred in the interior of the specimen prior to gross fracture initiation on the free surfaces. The final failure of the side ligaments happened because of shear lip formation. The tunneled region is characterized by a flat, fibrous fracture surface. In this paper, the experiments of [5] (corresponding to 5 m/s impact speed) are analyzed using a plane strain, dynamic finite element procedure. The Gurson constitutive model that accounts for the ductile failure mechanisms of micro-void nucleation, growth and coalescence is employed. The time at which incipient failure was observed near the notch tip in this computation, and the value of the dynamic J-integral, J d, at this time, compare reasonably well with experiments. This investigation shows that J-controlled stress and deformation fields are established near the notch tip whenever J d , increases with time. Also, it is found that the evolution of micro-mechanical quantities near the notch root can be correlated with the time variation of J d .The strain rate and the adiabatic temperature rise experienced at the notch root are examined. Finally, spatial variations of stresses and deformations are analyzed in detail.

Impact response and failure mechanisms of ultrahigh modulus polyethylene fiber composites and polyethylene fiber-carbon fiber hybrid composites

The impact response and failure mechanisms of ultrahigh modulus polyethylene (UHMPE) fiber composites and UHMPE fiber-carbon fiber hybrid composites have been investigated. Charpy impact, drop weight impact and high strain rate impact experiments have been performed in order to study the impact resistance, notch sensitivity, strain rate sensitivity and hybrid effects. Results obtained from dynamic and quasi-static measurements have been compared. Because of the ductility of UHMPE fibers, the impact energy absorption of UHMPE fiber composites is very high, thereby leading to excellent damage tolerance. By hybridizing with UHMPE fibers, the impact properties of carbon fiber composites can be greatly improved. The impact and shock failure mechanisms of these composites are discussed.

Micromechanics analysis of particulate-reinforced composites and their failure mechanisms

Stress fields and failure mechanisms have been investigated in composites with particles either surface treated or untreated under uniaxial tension. Previous experimental observation of failure mechanisms in a composite with untreated particles showed that tensile cracks occurred mostly at the polar region of the particle and grew into interfacial debonding. In a composite with surface-treated particles, however, shear yielding and shear cracking proceeded along the interphase-matrix interface at the polar area of the matrix and thus may improve the mechanical behaviour of the material. The finite element calculations showed that octahedral shear stress at the polar and longitudinal areas of the particle treated by coupling agents is much larger than that of materials with untreated particles, and the shear stress distribution around the interface is sensitive to the interphase property. The results suggest that a th ree-phase model can describe the composites with surface-treated fillers.