Fiber blank woven as a single piece by three-dimensional weaving to make a closed box-structure platform out of composite material for a turbine engine fan

A fiber blank woven as a single piece by three-dimensional weaving for making a platform of closed box structure out of composite material for a turbine engine fan, the fiber blank having opposite surfaces and comprising:

• a first portion, a second portion, and a third portion, each comprising a plurality of layers of weft yarns and each forming a portion of the thickness of the fiber blank between its opposite surfaces, the weft yarns of the fiber blank being arranged in columns, each column having weft yarns in all three portions;
• in each plane of the fiber blank, a set of warp yarns interlinking the layers of weft yarns of the first portion, of the second portion, and of the third portion, while forming:
• a closed non-interlinked zone separating the first portion from the second portion over a fraction of the dimension of the fiber blank in the warp direction between an upstream non-interlinking limit and a downstream non-interlinking limit;
• and
• at least one open non-interlinked zone separating the second portion from the third portion over a fraction of the dimension of the fiber blank in the warp direction from a non-interlinking limit to a downstream edge of the fiber blank;
• one or more first warp yarns interlinking layers of weft yarns in the first portion of the fiber blank adjacent to the closed non-interlinked zone, and layers of weft yarns in the second portion of the fiber blank before and after the closed non-interlinked zone;
• one or more second warp yarns interlinking layers of weft yarns in the second portion of the fiber blank adjacent to the open non-interlinked zone, and layers of weft yarns in the first portion of the fiber blank before and after the closed non-interlinked zone;
• one or more third warp yarns interlinking layers of weft yarns in the second portion of the fiber blank adjacent to the open non-interlinked zone, and layers of weft yarns in the third portion of the fiber blank before the open non-interlinked zone;
• and
• one or more fourth warp yarns interlinking layers of weft yarns in the third portion of the fiber blank adjacent to the open non-interlinked zone, and layers of weft yarns in the second portion of the fiber blank before the open non-interlinked zone,
• wherein except in the closed non-interlinked zone and in the open non-interlinked zone, the layers of weft yarns are interlinked by warp yarns over a plurality of warp yarn layers.