Key Engineering Materials Vols. 417-418

Abstract: In this paper, the concepts of preventive maintenance are pres¬ented in first part, and second part of the paper present several mathematical models for prediction service life as a base for preventive maintenance forecasting. These models aid in determining the frequency of inspec¬tions that will allow the condition of a piece of equipment to be determined in order to plan an appropriate maintenance action. The problem of determination of the service life is directly related to geometry, multiaxial loadings, materials and appropriate models for prediction of the failure propagation. The more precise modelling of these input parameters the more precise and reliable the results are. Therefore in the paper we will present models and procedures for calculations service life, remain service life and/or service control cycle.

Abstract: The fracture properties of the thermo-setting materials of epoxy asphalt mixture were evaluated based on J-integral concept and ultimate strength and compared to that of HMA with thermo-plastic binder materials. Totally 60 specimens cored from SGC with different notches were tested with SCB test under a temperature of -10°C and 20°C. The experimental results reveals that epoxy asphalt mixture has a super higher resistance of fracture at low temperature than thermo-plastic HMA due to its super high tensile strength and flexibility, and the influences of temperature on the fracture resistance of EAM is not so significant as that of thermo-plastic HMA. Good repeatability of SCB test results indicates the capability of the SCB test to be useful for measuring the fracture toughness of epoxy asphalt mixture.

Abstract: A stochastic damage constitutive model is proposed based on Kelvin spring-damper model and Li Jie spring stochastic damage model. The model is made up by microscopic spring-slipper element. The slipper, parallel connected with spring, is introduced to consider the plasticity effect of concrete. Damage failure process of concrete subjected uniaxial tension is divided into spring broken state and slipper broken state to describe the elastic stage and plastic stage of damage respectively. In the light of energy conservation during the process of damage failure, stochastic damage constitutive equation of concrete material subjected to uniaxial tension stress is derived. Comparisons between test results and theoretical calculation results verify that the established constitutive damage equations are accord with the experimental situation, and the experimental data are observed undulated with theoretical curve in the range of variance. The research results can apply in the actual engineering.

Abstract: The seismic performance and seismic damage model for steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns subjected to constant axial load and cyclically variety flexural loading was investigated experimentally. The main influencing parameters, including shear span ratio, axial compression ratio, stirrup ratio and concrete strength, on the seismic performance and seismic damage of the SRHSHPC frame columns is studied. From the test results, the failure mechanism is analyzed and damage quantization criterion is obtained. Several existing seismic damage models are comparatively analyzed. And then, the variation history of accumulated hysteretic energy of the specimens under different loading cycle indexes is figured out, and influence of different test parameters on it is also discussed. Finally, the damage index of the SRHSHPC columns is compared to the existing seismic damage models, and the double variables seismic damage model adapted for the SRHSHPC structure is established by statistical regression theory. The rule of damage evolvement for the specimens is proposed employing variation history of the damage index under different loading cycle indexes. The analytical results indicate that the seismic performance of the SRHSHPC composite column is good, and the double variables damage model could give a quantitative description for damaging process of the samples, which is a reference for seismic damage design of the SRHSHPC structure.

Abstract: The objective of this study is to investigate and develop a methodology to predict fatigue crack initiation and propagation in metallic laminate structures. The fatigue crack initiation is based on strain-life approach. After a crack has initiated, Stress Intensity Factors (SIF) are obtained and the subsequent propagation is described following Paris law type equations (NASGRO). Detailed Stress-Strain distribution in each layer is obtained from FE models, including the effect of the transition from flat to slant cracks on the fatigue crack growth.

Abstract: It is a fundamental response of any polymeric foam material to undergo non-recoverable deformation following the application of a defined compressive strain, exacerbated by temperature and humidity. This process is commonly referred to as compression set. The ability to predict recovery after the application of a compressive strain is crucial to both the manufacturers and end users of foam materials. Specific compression set test procedures have been established to quantify the extent of non-recoverable deformation in specific foam types but to date no general predictive approach exists. In this work, compression set (fixed strain) tests were undertaken on a cellular polyamide-6 material at various temperatures (-5°C to 90°C) and the foam recovery monitored over time periods in excess of those dictated by standard methods (ISO 1856 [1]). An empirical formula has been proposed to allow the prediction of recovery after compressive strain, covering recovery periods from 10 minutes to 24 hours (up to 168 hours at 23°C).

Abstract: The pipe-plate welding is a common type of joint in almost all industries. However the presence of residual stresses can be detrimental to the performance of the welded product. Therefore a good method for accurate estimation of the welding residual stress is needed. In this paper, three-dimensional finite element analysis is carried out to simulate pipe-plate structure. Based on the ANSYS software, the residual stress distribution of the pipe-plate structure during welding and after welding is predicted. The calculation results show that the residual stress of weld bead is higher than other places. The radial stress, hoop stress and axial stress are not significantly sensitive to the angle.

Abstract: Nickel-titanium alloy wires are widely applied in manufacturing biomedical devices; however, it is difficult to be micro-fabricated. Chemical etching process can successfully micro-fabricate the Ni-Ti alloy. The surface morphology, the etching products and the mechanical properties of the fine NiTi wires after the chemical etching process are investigated in the paper. After etching process, the characteristics of the wire surface are studied by Scanning Electron Microscopy (SEM). The X-Ray Diffraction (XRD) phase identification analysis is used to identify the etching products on the side surface of the etched wire. The Vickers Micro-hardness Test shows that the micro-hardness in peripheral surface is slightly higher than that in bulk. Mechanical properties of NiTi alloy fine wires after etching were studied by means of tensile tests.

Abstract: The inherent low tensile strength and shrinkage result in cracking of concrete under work loads. A new way to improve cracking properties is distributing steel fibers into expansive concrete to form a type of composite which is called steel fiber reinforced expansive concrete. This type of high performance concrete could compensate shrinkage as well as improving crack strength. For this concrete, the key point to ensure high performance and safety of concrete structure is to keep a stable expansive deformation during long-term service. A series of tests were carried out to measure long-term restrained expansive deformations of steel fiber reinforced expansive concrete with ages under various restrictions like steel bars and steel fibers. The test investigated some 3-year specimens. For all specimens, test parameters included 2 ratios of steel bar reinforcement, 4 volume fractions of steel fiber and 4 dosages of expansion admixture. The test results showed that the expansion of concrete decreased with increasing of steel bar reinforcing ratio as well as steel fiber volume fraction. In addition, when being in a lower dosage of expansion admixture, the specimens presented remarkable retraction of the expansive deformation. However, when beyond a certain dosage of expansion admixture, the long-term expansive deformation had less change with ages and almost remained the same with 90-day deformation, namely less losses of deformation. Hence, for steel fiber reinforced expansive concrete, using an appropriate dosage of expansion admixture could meet the requirements of designed strengthening and compensating shrinkage.

Abstract: This work investigates the possibility to perform Water Jet Peening (WJP) by means of a standard Water Jet (WJ) cutting plant. The experimentation is carried out on 39NiCrMo3 specimens with the aim to find out the best working conditions of two different methods: the in air-WJP and the submerged-WJP. Comparisons between the two methods and to previous experimentations in the reference literature are also presented.