Abstract A continuum based numerical approach is used to investigate the effects of slow and high-speed heating, including the ISO 834 fire curve, on thermal cracking of granite. During slow heating, thermal stress variations are mainly controlled by the heterogeneous thermal expansion of mineral grains. As a result, the stress concentrations are more isolated and dispersedly distributed throughout the sample. High-speed heating produces large thermal gradients especially at the outer surface of the samples, inducing big thermal strain increments and subsequent high compressive stresses. Larger cracks are formed due to a wider range of concentrated tensile stresses inside the sample during high-speed heating. At low temperatures, slow heating has a stronger influcence on micro-cracking. Due to larger cracks and newly induced micro-cracks, high-speed heating has an increasingly important impact on crack pattern in granite at high temperatures. Although shear failures show a significant increase at 800 °C, tensile cracks are still the majority of total failures in both, slow and high-speed heating scenarios. The final crack pattern in granite under fire conditions is a result of different cracking behaviors caused by various heating rates. This consequently affects strength and final failure pattern of granite.

中文翻译：

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慢速和高速加热条件下花岗岩的热损伤演化

摘要 基于连续介质的数值方法用于研究慢速和高速加热（包括 ISO 834 燃烧曲线）对花岗岩热裂纹的影响。在缓慢加热过程中，热应力变化主要受矿物颗粒的不均匀热膨胀控制。因此，应力集中在整个样品中更加孤立和分散。高速加热会产生大的热梯度，尤其是在样品的外表面，导致大的热应变增量和随后的高压缩应力。由于在高速加热过程中样品内部的集中拉伸应力范围更广，因此会形成更大的裂纹。在低温下，缓慢加热对微裂纹的影响更大。由于较大的裂纹和新诱发的微裂纹，高速加热对高温下花岗岩的裂纹模式产生越来越重要的影响。尽管剪切破坏在 800 °C 时显着增加，但在慢速和高速加热情况下，拉伸裂纹仍然是总破坏的主要部分。花岗岩在火灾条件下的最终裂纹模式是由不同加热速率引起的不同裂纹行为的结果。因此，这会影响花岗岩的强度和最终破坏模式。花岗岩在火灾条件下的最终裂纹模式是由不同加热速率引起的不同裂纹行为的结果。因此，这会影响花岗岩的强度和最终破坏模式。花岗岩在火灾条件下的最终裂纹模式是由不同加热速率引起的不同裂纹行为的结果。因此，这会影响花岗岩的强度和最终破坏模式。