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Rubber products are typically subjected to cyclic fatigue loading in service. During prolonged exposure to cyclic loading, damages initiate at intrinsic defect sites at microscopic levels and subsequently propagate, leading to catastrophic failure. Therefore, the material that offers better resistance to fatigue crack growth (FCG) is suitable for a durable product. FCG characteristics of rubber compounds depend on many factors, such as constituent material (rubber, filler, etc.) and environment and operational conditions (loading amplitude, loading pattern, etc.). To simulate the realistic service condition of a product, the choice of loading pattern is a key factor and has emerged as a very important research topic in recent times. The present work focuses on the effect of loading pattern on FCG characteristics of tire tread rubber compounds. In the present study, FCG characteristics of a 100% natural rubber (NR) compound were measured on a tear and fatigue analyzer (TFA, Coesfeld, Germany) using double edge notched pure shear specimen. Fatigue loading was applied using sinusoidal and pulse waveforms over a wide range of tearing energy levels. Pulse mode recorded a very high crack growth rate (∼2 times) compared to sine mode at equivalent peak energy levels. In order to understand the mechanics of the higher crack growth rate in pulse mode, finite element analysis (FEA) of a pure shear specimen was performed wherein FCG experimental conditions were used as boundary conditions. FE analyses were carried out using both linear and nonlinear viscoelastic material models. Nonlinear viscoelastic FEA results revealed that viscous energy dissipation at the crack tip is much lower in the case of pulse mode, which is in support of higher the FCG rate in pulse mode as observed in the experiments.

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Background Indomethacin has shown to be a broad spectrum anti-viral agent apart from it being a non-steroidal anti-inflammatory drug (NSAID). This randomized clinical trial in a hospital setting is to evaluate the efficacy and safety of this drug in RT-PCR positive Covid patients. Materials and Methods RT-PCR positive Covid-19 patients, who gave the consent for the trial, were allotted to a control, or case, arm based on block randomization procedure. The control arm received the standard care consisting of paracetamol, ivermectin and other adjuvant therapy. The case arm had indomethacin instead of paracetamol, retaining the other medications. The endpoint was the development of hypoxia/desaturation. Secondary endpoints were time to become afebrile and time to resolution of cough and myalgia. The results of 210 patients were available at this point, with 102 patients in the indomethacin arm and 108 in the paracetamol arm. The complete patient profile along with everyday clinical parameters were monitored. Blood chemistry at the time of admission and discharge were also carried out. Results As no one required high-flow oxygen, desaturation with an SpO2 level of 93 and below was considered an important goal. In the indomethacin group, no one out of the 102 patients developed desaturation. On the other hand, 20 of the 108 patients in the paracetamol arm developed desaturation. Patients who received indomethacin also experienced more rapid symptomatic relief compared to those in the paracetamol arm, with most symptoms disappearing in half the time. A total of 56 patients out of 108 in the paracetamol arm had fever on the seventh day, while no one recorded fever in the indomethacin arm. No adverse event was reported in either arms. A fourteenth day follow up revealed that the paracetamol arm patients had several discomforts including myalgia, joint pain and tiredness while the indomethacin arm patients complained only of tiredness. Conclusion Indomethacin is a safe and effective drug for the treatment of mild and moderate Covid-19 patients.