The construction of a forming limit diagram (FLD) is a conventional approach to obtain limit strains and to evaluate the formability of sheet metal. Appropriate necking criteria should be applied to determine the forming limit curve (FLC) accurately. In recent years, deep research on the determination of the FLC has been carried out; meanwhile, several necking criteria have been proposed. However, the application of inappropriate necking criteria would cause deviations when determining FLCs. In this study, both Marciniak and Nakajima tests were carried out on the AA5086 aluminum sheet to make a comparative investigation of different necking criteria in the determination of FLCs. In the Marciniak test, four existing necking criteria were chosen to construct FLCs, and analyzed in detail. The well-performed time dependent and position dependent methods were selected for the Nakajima test. Meanwhile, the modified Wang method based on the height change of the adjacent points was proposed. The comparative results showed that the time and position dependent methods were relatively conservative in both experiments, while the modified Wang method could identify the onset of localized necking more accurately.

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A quadri-specific hybrid F 1 (G.arboreum, G. herbaceum, G.hirsutum, and G.barbadense) was produced by crossing the doubled-chromosome (G.arboretum 6 G. herbaceum) F 1 with (G.hirsutum 6 G.barbadense) F 1 . The hybrid plants were preserved for 15 years via the method of grafting. The hybrid flowers were self-crossed and back-crossed every year, and the pollen vigor was tested as well. The results showed that the percentage of fertile pollens and weak-vigor pollens increased with the time of plant preservation, especially for those of weak-vigor that occupied about 10% of the total pollens after 15 years of growth. Meanwhile, the percentage of the sterile pollens decreased with the plant preservation, and the fertility of the quadri-specific hybrid was recovered partially. After plant preservation for more than 10 years, some backcrossed seeds were obtained via backcrossing with upland cotton parents, and a few self-crossed seeds were produced finally. The characteristics of chromosome behavior and the chromosome configuration during the meiosis were studied and the results showed that the chromosome configuration of the quadri-specific hybrid plant grown for 15 years was 2n 5 52 5 4.92I + 14.62II + 2.29III + 1.56IV + 0.71V + 0.19VI, while that from the plants of 15 years ago was 2n 5 52 5 8.4I + 8.1II + 5.7III + 1.9IV + 0.6V. It was showed that the univalents decreased to 3.5 per cell, bivalents increased up to 6.5 per cell, and the number of multivalents decreased obviously as well. It was found from this experiment that extending the growth period by the method of grafting would be helpful to harmonize the relationship among the different chromosome groups which came from different species, and balance the chromosome configuration, which led to the partially recovering in plant fertility of the interspecific hybrids.