In this paper, a procedure based on digraph and matrix approach is presented for carrying out life cycle design and evaluation of mechanical systems, at system conceptual design stage. Features which characterize life cycle aspects of the system are identified and are called attributes of life cycle of a the system. Consideration of these attributes and their interrelations are rudiment in design and evaluation of life cycle of the system. This is modeled in terms of life cycle Design (LCD) attributes digraph for the system. Nodes in the digraph represent attributes and their relations are represented by their edges. The digraph is represented by one-to-one matrix for development of life cycle design (LCD) expression, which is characteristics of the system. A variable life cycle design attributes permanent matrix is defined to develop VPF-d which is also useful in comparing two design concepts of the system. Life cycle design Index (LCD-I) is obtained from permanent of the matrix or from the LCD expression by substituting numerical values of the attributes and their interrelations. A higher value of the index implies good LCD of the system. The ideal value of LCD index (III) is also obtained from the matrix expression, which is useful in assessing the relative LCD, of the system alternatives. The procedure is useful in design and development of LCD of the system. A step by step procedure for evaluation of LCD index is also suggested and is illustrated by means of an example.

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