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In this work, the response of an ammonium perchlorate (AP)‐hydroxyl‐terminated polybutadiene (HTPB) composite material under impact loading is presented, utilizing computational cohesive finite element method (CFEM) simulations that are validated with drop hammer experiments. This study examined the impact behaviour of AP crystal sizes between 200 and 400 μm by varying impact velocities between 3 and 10 m/s. Based on the outcome of CFEM simulations, analysis of variance (ANOVA) tests and a response surface method (RSM) were utilized to construct a mathematical model approximating the relationships between simulation inputs and outcomes. Both computational and experimental results show that the local strain rate has a considerable positive correlation with crystal size, and the rate of temperature change has positive correlations with both crystal size and impact velocity. Further, it was observed that stiffness and compression energy are the primary factors to variances in local strain rate and rate of change of temperature. RSM has been found to be an effective tool for modelling impact responses of materials under varying experimental conditions. [ABSTRACT FROM AUTHOR]

Ethylene oxide (EtO), although banned for use, is still being detected in foodstuffs that have been fumigated to eradicate pests during storage and transport. Residual levels over the European Union's (EU) maximum residue limit (MRL) pose severe health concerns. Recent detection of EtO and its by-product 2-chloroethanol (2-CE) at alarming levels have led to product recalls throughout the EU. Here, a simple, automated headspace (HS)-trap method for the simultaneous determination of EtO and its derivative 2-CE by gas chromatography-mass spectrometry (GC-MS) at the required MRL of ≤ 0.05 mg/kg has been implemented. Syringe-based HS combined with backflushed trapping technology provided enrichment of multiple extractions from the same sample vial (known as multi-step enrichment or MSE®) to increase sensitivity for EtO and 2-CE analysis by GC-MS using single-ion-monitoring (SIM) mode. Method detection limits (MDLs) of 0.00059 mg/kg and 0.00219 mg/kg for EtO and 2-CE, respectively, were obtained without the need for manual handling, solvent extraction or derivatization methods. Recoveries were shown to average (n = 5) at 98% and 107% for EtO and 2-CE, respectively, and the reproducibility was <10% for both compounds. [ABSTRACT FROM AUTHOR]

Abuse of Lithium-ion batteries, both physical and electrochemical, can lead to significantly reduced operational capabilities. In some instances, abuse can cause catastrophic failure, including thermal runaway, combustion, and explosion. Many different test standards that include abuse conditions have been developed, but these generally consider only one condition at a time and only provide go/no-go criteria. In this work, different types of cell abuse are implemented concurrently to determine the extent to which simultaneous abuse conditions aggravate cell degradation and failure. Vibrational loading is chosen to be the consistent type of physical abuse, and the first group of cells is cycled at different vibrational frequencies. The next group of cells is cycled at the same frequencies, with multiple charge pulses occurring during each discharge. The final group of cells is cycled at the same frequencies, with a partial nail puncture occurring near the beginning of cycling. The results show that abusing cells with vibrational loading or vibrational loading with current pulses does not cause a significant decrease in operational capabilities while abusing cells with vibrational loading and a nail puncture drastically reduces operational capabilities. The cells with vibration only experience an increase in internal resistance by a factor of 1.09–1.26, the cells with vibration and current pulses experience an increase in internal resistance by a factor of 1.16–1.23, and all cells from each group reach their rated lifetime of 500 cycles without reaching their end-of-life capacity. However, the cells with vibration and nail puncture experience an increase in internal resistance by a factor of 6.83–22.1, and each cell reaches its end-of-life capacity within 50 cycles. Overall, the results show that testing multiple abuse conditions simultaneously provides a better representation of the extreme limitations of cell operation and should be considered for inclusion in reference test standards. [ABSTRACT FROM AUTHOR]

In this article, the dynamic response of a heterogeneous microstructure of polymer bonded composite was analyzed to a short duration shock pulse. The composite microstructure studied is a polymerbonded sugar (PBS) with single-crystal sucrose embedded inside the polydimethylsiloxane binder. The shock pulse was created by the impact of the aluminum disk at high speeds using a laser-based projectile launch system. The mechanical response on the microscale domain was measured using ultrafast time-resolved Raman spectroscopy. The in-situ analysis of the change in Raman spectra from PBS during shock compression was captured in the time domain using a streak camera. The results show a steeply rising shock front after the impact where the shock pressure rise time was estimated from the time-resolved Raman spectra. The viscoplastic behavior in the local microscale domain was characterized by quantifying effective shock viscosity measured in the vicinity of the crystal-binder interface.

In this work, microstructure dependent impact-induced failure of hydroxyl-terminated polybutadiene (HTPB)–cyclo-tetra-methylene-tetra-nitramine (HMX) energetic material samples is studied using the cohesive finite element method (CFEM). The CFEM model incorporates experimentally measured viscoplastic constitutive behavior, experimentally measured interface level separation properties, and phenomenological temperature increase due to mechanical impact based on viscoplastic and frictional energy dissipation. Nanoscale dynamic impact experiments were used to obtain parameters for a strain-rate dependent power law viscoplastic constitutive model in the case of bulk HTPB and HMX as well as the HTPB–HMX interfaces. An in situ mechanical Raman spectroscopy (MRS) setup was used to obtain bilinear cohesive zone model parameters to simulate interface separation. During analyses, the impact-induced viscoplastic energy dissipation and the frictional contact dissipation at the failed HTPB–HMX interfaces is found to have a significant contribution toward local temperature rise. Microstructures having circular HMX particles show a higher local temperature rise as compared to those with diamond or irregularly shaped HMX particles with sharp edges indicating that the specific particle surface area has a higher role in temperature rise than particle shape and sharp edges. Regions within the analyzed microstructures near the HTPB–HMX interfaces with a high-volume fraction of HMX particles were found to have the maximum temperature increase. [ABSTRACT FROM AUTHOR]