An experimental and numerical evaluation on the dynamic compressive response of mortars containing up to 20% waste iron powder as sand replacement is presented in this paper. The dynamic response is evaluated using split Hopkinson pressure bar (SHPB) apparatus under high strain rates (up to 250/s). The elongated iron particulates present in the iron powder-incorporated mortars warrant significantly improved compressive strength and energy absorption capacity at high strain rates. Multiscale numerical simulations are performed with a view to develop a tool that facilitates microstructure-guided design of these particulate-reinforced mortars for efficient dynamic performance. The dynamic compressive response of particulate-reinforced mortars is simulated adopting a numerical approach that incorporates strain rate-dependent damage in a continuum micromechanics framework. The simulated dynamic compressive strengths and energy absorption capacities for mortars with various iron powder content exhibit good correlation with the experimental observations thereby validating the efficacy of the simulation approach.
Impact problems are usually interesting for the military, either for defensive or offensive purposes to develop armor or ammunition. Recently, daily applications request safety of the products, therefore, it is essential to understand the material behavior under intense short duration or impact loadings. Metallic armor is extremely heavy and would not be popular for personal protection. However, reinforced fiber composites have been used for these purposes. In present study, carbon-fiber-reinforced aluminum honeycomb, aramid and plywood materials were used for armor matrix layers. For determining the capability of sequencing the composite layers, ballistic tests for all six combination of sequenced sandwich panels for three different composites were evaluated at a speed of 700 m/s using a 36 caliber one-cored projectile. To obtain cheaper and reliable solutions for further studies of various test conditions, computer aided ballistic simulations were analyzed. To make sufficient correlations, the test results and the computer simulations were compared to each other. Finally, plywood used between the aramid and the carbon-fiber-reinforced aluminum honeycomb sandwich panel has shown the most accurate and the reliable results of the tests and the computer simulations.
This paper investigates the dynamic compressive behavior of wollastonite fiber-reinforced cementitious mortars using multiscale numerical simulations. The rate dependent behavior of the multiphase heterogeneous systems is captured in a multiscale framework that implements continuum damage towards effective property prediction. The influence of wollastonite fiber content (% by mass) as cement replacement on the dynamic compressive strength and energy absorption capacity is thereafter elucidated. An average compressive strength gain of 40% is obtained for mortars with 10% wollastonite fiber content as cement replacement, as compared to the control mortar at a strain rate of 200/s. The rate dependent constitutive responses enable the computation of energy absorption, which serves as a comparative measure for elucidating the material resistance to impact loads. Approximately a 45% increase in the dynamic energy absorption capacity is observed for the mixture containing 10% wollastonite fibers, as compared to the control case. Overall, the study establishes wollastonite fibers as a sustainable and dynamic performance-enhanced alternative for partial cement replacement. Moreover, the multiscale numerical simulation approach for performance prediction can provide an efficient means for the materials designers and engineers to optimize the size and dosage of wollastonite fibers for desired mechanical performance under dynamic loading conditions.
By modifying the present test-tube method of high-temperature aging to permit air circulation by convection, the test is made appreciably more severe, but at the same time more reproducible. The velocity of air circulation under the conditions used here, which varied over a three-fold range from 1.1 to 3.4 changes of air per hour, did not affect the results obtained. The loss in weight during aging was somewhat greater in the circulating-air tests than in the stoppered-tube tests. The poorer reproducibility of the stoppered test-tube method over the circulating-air method is thought to be due to variations in the permeability of the stoppers used. The more impermeable the stopper, the less severe is the test. It is recommended that the present test-tube aging method D-865 be amended to require the use of a pair of glass tubes extending through the stopper using the dimensions and arrangement illustrated in Figure 1.
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