The mechanics of the failure process and ultimate strength of a twisted yarn structure are studied using a newly proposed stochastic model of the failure process. The importance of the twist reinforcing mechanism to the strength of a twisted structure with continuous components, the interaction patterns between different component types during yam extension, and the significance of multiple breaks along a component are demonstrated. Building on the three basic concepts of fragmentation and chain-of-subbundles, changing lateral constraint between components due to twist and its effect on component strength, and load sharing between broken and still surviving members during yam breakage, a new mechanistic approach is proposed and a stochastic computer model is developed to predict the behavior of blended yams. The approach is similar to that developed earlier by Boyce et al. [3] to study the failure process in woven fabrics. The model acts to predict the strength and fracture behavior of a blended yarn with continuous components. The predicted results are illustrated in comparison with the experiments of Monego et al. [20,21,22]. By means of this new model, fundamental features of blended yam behavior are simulated and elucidated, including the strength reinforcing mechanism of twist in a blended yam, the yarn break propagation pattern, and the effect of twist on yam fracture behavior as well as the shape effect of component stress-strain curves. Moreover, the relationship between the strength of a structure and that of its components is also investigated. Fiber blending has traditionally been considered an effective means for improving or reinforcing mechanical as well as other properties of yarns. The study of blended continuous-filament structures has attracted the attention of many researchers [2,15,19,20,21,22,23]. The purpose of such study is to understand the role of various phenomena contributing to the mechanical behavior of the blend, including the reinforcing mechanism of fiber blending, the interactions of the different constituent fibers in a hybrid twisted structure under external load as well as the effect of lateral pressure on fiber interaction, the relation and mechanism between yarn strength and blend ratio, and the effect of twist level on the fracture behavior of blended yarn. Ultimately, results from these studies will provide theoretical foundations for predicting the ultimate strength and fracture behavior of blended filament yams. This is significantly important to textile science, and could potentially help fiber producers and textile firms guide fiber processing and optimize textile blending and spinning techniques.Many investigators have focused on filament yams, not only because the filament structure has considerable significance for certain industrial applications, but because the study of continuous filament yarns is also mathematically more manageable compared with staple yarns, and will certainly provide a basis for further development of the theory for staple yarns.Research on the...