Mechanism of crack initiation and propagation of re-entrant auxetic honeycombs under thermal shock

Thermal shock multiple cracking behaviors of re-entrant auxetic honeycombs with a negative Poisson's ratio are investigated, and the crack initiation and propagation behavior are discussed. An effective macro continuum model is developed to detect the effects of cracking density and microstructures of auxetic honeycombs on the thermal stress and intensity. The microscale tensile stresses in the struts ahead of the crack as functions of the corresponding thermal stress intensity factor (SIF) at the macroscale are evaluated by employing a macro-micro model. Then, a lower-bound method is proposed to assess the critical thermal load of auxetic honeycombs by combining the macro-micro model and the macro continuum model. A significant increase in both transient thermal stress and intensity as the growing cell-wall angle is demonstrated. Results for the maximum thermal SIF as well as the maximum tensile stress in the middle of cracks are calculated as functions of crack density and length. With the identical SIF, the microscale tensile stresses ahead of the crack in honeycombs with smaller cell-wall angles are greater than that in mediums with larger angles due to the more significant crack tip opening displacement. Critical thermal load prediction reveals that the honeycombs with smaller cell-wall angles generally possess more excellent thermal shock resistance. Also, the varying failure modes of different auxetic honeycomb strips under specific thermal load are predicted. The corresponding crack initiation and propagation mechanisms are revealed.

Kajian Analisis Respon Struktur Bangunan Baja di Bawah Pengaruh Kombinasi Beban Termal (Kebakaran) dan Beban Angin. (Hal. 13-25)

ABSTRAKBeban termal yang terjadi pada bangunan dapat mengakibatkan degradasi pada struktur baja dan menyebabkan keruntuhan. Penelitian ini menganalisis pengaruh beban termal disertai beban angin terhadap respon dari struktur bangunan baja lima belas lantai yang berfungsi sebagai perkantoran dengan mempertimbangkan degradasi propertis baja, reduksi beban hidup dan beban mati tambahan, serta kecepatan penanganan pemadaman. Simulasi terbagi menjadi tiga kasus yaitu penanganan pemadaman kebakaran cepat, penanganan pemadaman kebakaran lambat, dan penentuan beban termal kritis. Analisis struktur dilakukan dengan bantuan software ETABS. Hasil simulasi kebakaran menunjukkan semakin tinggi temperatur maka stress ratio dari elemen struktur makin membesar. Pada penentuan beban termal kritis diperoleh bahwa besar beban termal yang dapat menyebabkan minimal satu elemen struktur utama mengalami kegagalan pada umumnya berbeda pada lantai level bawah, tengah, dan atas. Pada studi kasus ini diperoleh beban temperatur kritis paling besar yaitu pada lantai level atas.Kata kunci: beban termal, degradasi propertis baja, kegagalan struktur ABSTRACTThermal load on the building can lead into the degradation of steel structure and cause collapse. This study analyze the effect of thermal along with wind loads on the response of fifteen stories steel structure building which serves as an office by considering the degradation of steel properties, the reduction of live load and super imposed dead load, and the speed of handling the extinguishing. This simulation is divided into three cases which are fast handling of extinguishing, slow handling of extinguishing, and the determination of the critical thermal load. Structural analysis will be done using the ETABS software. The result of fire simulation showed that when the temperature is higher, the stress ratio of structural elements will also expand. In the determination of the critical thermal load, it is obtained that the thermal loads which can cause failure in minimum one major structural element are generally different at the bottom, middle, and top level of stories. In this case study, the highest critical temperature load is on the top level.Keywords: thermal load, steel properties degradation, structure failure