Damage Detection in Reinforced Concrete Berthing Jetty Using a Plasticity Model Approach

A conventional method of damage modeling by a reduction in stiffness is insufficient to model the complex non-linear damage characteristics of concrete material accurately.In this research,the concrete damage plasticity constitutive model is used to develop the numerical model of a deck beam on a berthing jetty in the Abaqus finite element package.The model constitutes a solid section of 3D hexahedral brick elements for concrete material embedded with 2D quadrilateral surface elements as reinforcements.The model was validated against experimental results of a beam of comparable dimensions in a cited literature.The validated beam model is then used in a three-point load test configuration to demonstrate its applicability for preliminary numerical evaluation of damage detection strategy in marine concrete structural health monitoring.The natural frequency was identified to detect the presence of damage and mode shape curvature was found sensitive to the location of damage.

New Methodology for Evaluating Toughness of Composite Laminates-Investigation of Damage Resistance

The existing problems in toughened resin evaluation technology, particularly the disadvantage of the toughened resin identification method by CAI, is pointed out based on the point of view of composite structure design. It is proposed to evaluate the toughness of composites by both damage resistance and damage tolerance. Seven different toughness composites are investigated by impact and quasi\|static indentation tests. Based on experimental data analysis, the parameter that is most sensitive to the damage resistance is determined as the damage parameter. The parameter to evaluate the damage resistance and its measuring method are proposed.

Dynamic Mechanical Characteristics and Damage Evolution Model of Granite

By using the technique of the split Hopkinson pressure bar（ SHPB）,impact tests at different stress wavelengths（ 0. 8-2. 0 m） and strain rates（ 20-120 s^（-1）） were conducted to study the dynamic mechanical properties and damage accumulation evolution lawof granite. Test results showthat the dynamic compressive strength and strain rate of granite have a significantly exponential correlation;the relationship between peak strain and strain rate is approximately linear,and the increase of wavelengths generally makes the level of peak strain uplift. The multiple-impacts test at a lowstrain rate indicates that at the same wavelength,the cumulative damage of granite shows an exponential increasing form with the increase of strain rate; when keeping the increase of strain rate constant and increasing the stress wavelength,the damage accumulation effect of granite is intensified and still shows an exponential increasing form; under the effect of multiple impacts,the damage development trend of granite is similar overall,but the increase rate is accelerating. Therefore the damage evolution model was established on the basis of the exponential function while the physical meaning of parameters in the model was determined. The model can reflect the effect of the wave parameters and multiple impacts. The validity of the model and the physical meaning of the parameters were verified by the test,which further offer a reference for correlational research and engineering application for the granite.

Bi-normalized response spectra and seismic intensity in Bucharest for 1986 and 1990 Vrancea seismic events

The Vrancea subcrustal earthquakes of August 30,1986 and May 30,1990 are the two most recent seismic events that have occurred in Romania with moment magnitudes M W ≥ 6.9.The spectral analysis of the strong ground motions recorded in Bucharest reveals that despite small differences in magnitude between the 1986 and 1990 earthquakes,their frequency contents are very different,sometimes even opposing.The main focus of this study is to conduct a comparative analysis of the response spectra in terms of the bi-normalized response spectra(BNRS) proposed by Xu and Xie(2004 and 2007) for strong ground motions recorded in Bucharest during these two seismic events.The mean absolute acceleration and relative velocity response spectra for the two earthquakes are discussed and compared.Furthermore,the mean bi-normalized absolute acceleration and normalized relative velocity response spectra with respect to the control period T C are computed for the ground motions recorded in Bucharest in 1986 and 1990.The predominant period T P is also used in this study for the normalization of the spectral period axis.Subsequently,the methodology proposed by Martinez-Perreira and Bommer(1998) is applied in order to estimate the seismic intensity of the two events.The results are discussed and several conclusions regarding the possibility of using the bi-normalized response spectra(BNRS) are given.

Determination of multiaxial stress rupture criteria for creeping materials:A critical analysis of different approaches

Materials in engineering applications are rarely uniaxially-loaded.In reality,failures under multiaxial loading has been widely observed in engineering structures.The life prediction of a component under multiaxial stresses has long been a challenging issue,particularly for high temperature applications.To distinguish the mode of failure ranging from a maximum principal stress intergranular damage to von Mises effective stress rupture mode a multiaxial stress rupture criterion(MSRC)was originally proposed by Sdobyrev and then Hayhurst and Leckie(SHL MSRC).A multiaxial-factor,α,was developed as a result which was intended to be a material constant and differentiates the bias of the MSRC between maxi-mum principal stress and effective stress.The success of the SHL MSRC relies on accurately calibrating the value ofαto quantify the multiaxial response of the material/geometry combination.To find a more suitable approach for determining MSRC,the applicability of different methods are evaluated.Given that the resulting analysis of the various approaches can be affected by the creep failure mechanism,princi-ples in the determination of MSRC with and without using continuum damage mechanics approaches are recommended.The viability of uniaxial material parameters in correlating withαthrough the analysis of available data in literature is also presented.It is found that the increase of the uniaxial creep dam-age tolerance parameterλis accompanied bythe decreaseof theα-value,whichimplies thatthe creep ductility plays an important role in affecting the multiaxial rupture behavior of materials.

Multiaxial fatigue life prediction of composite materials

In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.

Multiaxial fatigue life prediction of composite laminates

A study of composite laminates under tension–torsion biaxial loading is presented.The focus is placed on fatigue lives of composite laminates under different tension–torsion biaxial fatigue loading paths.A macro-meso model used to predict multiaxial fatigue life of composite laminates is also presented in this paper.Firstly,a macro-scale 3 D RVE corresponding to composite laminates is established to determine strain components in the material principal direction of each layer for each biaxial stress ratio.Secondly,a meso-scale 3 D RVE corresponding to each layer with fibers distributed randomly is established,with progressive damage prediction method,biaxial strength of composite laminates can be predicted,and the final failure layer can be confirmed.Thirdly,select any one of fatigue loading path at which the final failure of composite laminates is fiber failure(matrix failure)to establish the reference curve for fiber(matrix).Finally,with reference curve,fatigue life of composite laminates under any biaxial loading path can be predicted.And numerical results show good agreements with experimental data.