Finite element analysis of ballastless track slabs reinforced with fiber-reinforced polymer bars

Fiber-reinforced polymer–reinforced ballastless track slabs not only improve the insulation performance but also have advantages in their mechanical properties. The objective of the article is to propose a corresponding design method of the ballastless track slabs considering different parameters by a finite element analysis model. The deformation performance of the ballastless track slabs, as well as the prediction results of several models, was studied considering the different prestress levels, reinforcement ratios, and prestressed materials. The results show that ACI 440.4R-04 and Bischoff models are suggested for predicting the deflection of a ballastless track slab when the prestress level is between 30% and 60% and the Brown and Bartholomew model is suitable for those with a prestress level below 30%.

Effect of Applied and Residual Stresses on the Analysis of Mechanical Properties by Means of Instrumented Indentation Techniques

Various methods have been proposed in recent years for the determination of mechanical properties of a material by using instrumented indentation testing. These load and depth sensing indentation techniques imply the measurement of a characteristic load-indentation depth curve by the aid of which numerous materials properties can be extracted. On the other hand in many publications the effect of applied or residual stresses on the results of hardness readings is investigated. Methods are proposed to estimate applied or residual stresses by means of instrumented indentation testing. Based on this obvious inconsistency between these procedures on the use of information of instrumented hardness testing the influence of residual stresses as well as applied stresses on continuous microhardness readings is systematically investigated for steel samples. Experimental investigations were supplemented by finite element simulations of ball indentation tests on equi-biaxially prestressed materials states. These simulations show that the registered force-indentation depth curves as well as the geometry of the indentations are affected by loading and residual stresses in a characteristic way. For hardness values changes of up to 35% are determined with reference to the unstressed initial state.

Some Results in the Erosion of Prestressed Materials due to Water-Jet Impact

Two methods are described of applying uniaxial and biaxial tensile and compressive stresses to specimens subject to the erosive action of repetitive water jets which have speeds in the range 30–220 m/s. The influence which prestress has on erosion is examined in a ductile material, α-brass, and in a brittle material, Perspex. The behaviour of these materials contrasts sharply due to their different fracture modes. Also the values of prestress to impact stress ratio and the type of stress applied, are shown to have a bearing on results.

An Analysis of the Split Hopkinson Bar Technique for Strain-Rate-Dependent Material Behavior

The analysis of the split Hopkinson bar experiment for determining dynamic material behavior is examined for several specific examples of specimen materials which exhibit strain-rate-dependent mechanical behavior. The torsional mode of deformation is chosen as more closely representing a one-dimensional state of stress. Details of the propagation and reflection of stress waves within the specimen are studied using a numerical procedure based on the method of characteristics. Reconstituted stress-strain curves calculated from the conventional analysis of the split Hopkinson bar experiment are compared with actual material behavior for several simulated experiments involving variations in input stress, gage length, material behavior, and static stress-strain curves including statically prestressed materials. The validity of the experimental technique is discussed and limitations on its use are delineated.