Time-domain (TD) statistical features are frequently utilized in vibration-based pattern recognition (PR) models to identify faults in rotating machinery. Presence of possible fluctuations or spikes in random vibration signals can considerably affect the statistical values of the extracted features consequently. This paper discusses the sensitivity of TD features against the fluctuations occurred in vibration signals while classifying localized faults in ball bearing. Based on the sensitivity level, the features are statistically processed prior to employing a classifier in PR model. A central tendency-based feature pre-processing technique is proposed that enhances the diagnostic capability of classifiers by providing appropriate values. The feature processing reduces undesired impact of fluctuations on the diagnostic model. Several classifiers are utilized to evaluate the performance of the proposed method, and the results are evident of its effectiveness. The associated advantage of the feature pre-processing over the conventional pre-processing of raw data is its computational efficiency. It is worth mentioning that only few values in feature distributions are required to be processed rather than dealing with big TD vibration data set.

In this study, the ballistic impact behavior of auxetic sandwich composite human body armor was analyzed using finite element analysis. The auxetic core of the armor was composed of discrete re-entrant unit cells. The sandwich armor structure consisted of a front panel of aluminum alloy (Al 7075-T6), UHMWPE (sandwich core), and a back facet of silicon carbide (SiC) bonded together with epoxy resin. Numerical simulations were run on Explicit Dynamics/Autodyne 3-D code. Various projectile velocities with the same boundary conditions were used to predict the auxetic armor response. These results were compared with those of conventional monolithic body armor. The results showed improved indentation resistance with the auxetic armor. Deformation in auxetic armor was observed greater for each of the cases when compared to the monolithic armor, due to higher energy absorption. The elastic energy dissipation results in the lower indentation in an auxetic armor. The armor can be used safely up to 400 m/s; being used at higher velocities significantly reduced the threat level. Conversely, the conventional monolithic modal does not allow the projectile to pass through at a velocity below 300 m/s; however, the back face becomes severely damaged at 200 m/s. At a velocity of 400 m/s, the front facet of auxetic armor was destroyed; however, the back facet was completely safe, while the monolithic panel did not withstand this velocity and was completely damaged. The results are encouraging in terms of resistance offered by the newly adopted auxetic armor compared to conventional monolithic armor.