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首页> 外文期刊>Acta Horticulturae >Stresses and cracking in freezing part-baked bread: a numerical model.
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Stresses and cracking in freezing part-baked bread: a numerical model.

机译：冷冻部分烘焙的面包中的应力和破裂：一个数值模型。

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摘要

Thermal stresses caused by the volume expansion of water during freezing process of part-baked frozen bread have a direct impact on final bread quality. Crust flaking could be caused by differential strains within the loaf. In order to understand the thermomechanical behaviour of part-baked bread during freezing and to prevent this phenomenon, we modeled the part-baked bread freezing. Thermal stresses during freezing of part-baked bread were simulated with a hookean law, using realistic thermal and mechanical properties. The stress field is assumed to have no influence on heat transfer. Therefore, the temperature field was calculated first, and then the stress field is calculated based on it. It was found that to explain observed cracking patterns, both expansion due to phase change and subsequent thermal contraction must be taken into account. During freezing, the unfrozen core is always under uniform isotropic tensile stress, but that is unlikely to explain the cracking pattern. Cracking during cryogenic freezing is more likely due to tensile tangential stresses caused by thermal contraction, with vitrification at the surface possibly playing a role in crack initiation. The calculations suggest that once a crack forms at the surface it will propagate towards the centre, as has been observed experimentally.
机译：部分烘焙的冷冻面包在冷冻过程中水体积膨胀引起的热应力直接影响最终面包的质量。面包内的差异应变可能导致结皮剥落。为了了解部分烘焙的面包在冷冻过程中的热机械行为并防止这种现象，我们对部分烘焙的面包冷冻进行了建模。利用现实的热力学和机械特性，通过霍根定律模拟了半烘焙面包冷冻期间的热应力。假定应力场对传热没有影响。因此，首先要计算温度场，然后根据温度场计算应力场。已经发现，为了解释观察到的破裂模式，必须考虑由于相变引起的膨胀和随后的热收缩。在冻结过程中，未冻结的芯始终处于均匀的各向同性拉伸应力下，但这不可能解释开裂模式。低温冷冻过程中的开裂更可能是由于热收缩引起的拉伸切向应力引起的，表面的玻璃化可能在开裂中起作用。计算表明，如在实验中观察到的，一旦在表面形成裂纹，裂纹就会向中心传播。

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