There exist looseness phenomena in mechanical systems, including foundation looseness, pedestal looseness and component match looseness. The causes of the three types of looseness were explained with examples. Some common types of looseness models were summarized. Research status of six types of looseness, including single looseness, looseness coupled with rub-impact, looseness coupled with crack, looseness at two end-supports, looseness of rotor system with slowly varying mass, and looseness of double-span rotor system was elaborated in the aspects of dynamics modeling, solution meth-od and their nonlinear dynamic characteristics. Research of looseness experiments were also introduced briefly. Finally, the hot points for further study of the looseness faults were prospected.%松动现象广泛存在于机械系统中，包括基础松动、支座松动及部件间配合松动。为此举例说明了三类松动的故障成因，归纳了国内外研究中常见的几种松动模型，从松动故障的动力学建模、求解方法及其非线性动力学特性等方面，对单一松动、松动—碰摩耦合、松动—裂纹耦合、两端支座松动、质量慢变系统松动与双跨转子系统松动等六类松动问题的研究现状进行了阐述，并简要介绍了松动实验的研究现状。最后，对松动故障研究中的关键问题或进一步研究课题进行了展望。
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