# Systemic Evaluation of PSS in the Early Concept Phase Using Graph-Based Reasoning
## 5 Validation
### GEAR Method--Step 2: Elicitation of the Evaluation Logic  
EVCs and their metrics related to components of the same material flow are assessed using a unified evaluation logic based on input/output relationships. GEAR method step 2 was applied in a workshop with domain experts to develop this logic. The metal powder flow was analyzed, focusing on capturing and recycling it within the PSS, examining three main streams (routes of _internal recycling_, _external recycling_, and _disposal as scrap_). Preconditions and factors affecting recycling were also explored. The group reviewed each PSS function and EVC impacts, discussing dependencies across functions in detail. Figure 16 illustrates the causal map displaying identified relationships in natural language based on the discussions, grouped by the functional structure of the product service system (PSS). Two types of arrows indicate causal perspectives: a _procedural view_ for material flow and _dependency view_ for operational influences on the PSS. Influencing factors are categorized by type of influence, as identified in the workshop:  
* Technological Influences: These describe how technical systems within the PSS and the technical operational environment affect the amount of powder produced and how much of it can be recycled. * Company-Specific Influences: These refer to the organization, policies, and specific characteristics of the company that impact powder wastage and quality requirements for the powder. * Market Factors: These relate to the achievable prices for recyclable powder with third-party providers, which are crucial for the economic viability of integrating the process into the PSS. * Environmental Influences: These refer to the biosphere's impact, particularly how climatic conditions affect the quality of the AM process and resulting waste. * Service-Related Influence: This category pertains to factors that arise from the service aspect of the PSS. PSS recycling steps like powder collection and sieving are straightforward, needing no detailed causal descriptions from experts according to the principle of detailing. External powder recycling is handled by a service provider beyond the company's control and, therefore, is not detailed either. Instead, EVC fulfillment relies on the interaction between the PSS and the company's AM production process. Only critical and uncertain influences were documented. After understanding key influences and causal relationships, these were formalized based on available knowledge according to the GEAR method, adding semantic interpretations to the graph model as meta-information. To this end, the available sources of information for the identified relationships were first identified and reviewed; then, corresponding level of understanding for each influence was assessed. Experts' understanding of material flow was largely based on literature and other facilities of the company, including data from studies on lost metal powder in different machines. These data were used but normalized to a 100 kg reference charge and combined with an uncertainty factor representing them as a normal distribution, since they were data from another context. The measured amounts of powder lost at specific points (e.g., in machine  
Figure 15: Functional structure of the PSS considered to elicit the causal relationships relevant for the considered EVCs. filters, through depowdering, etc.) were used as mean values; then, plausible values for a standard deviation were defined by domain experts. In result the powder flow consists of many normal distributions for the amount of metal powder flow that are mapped in an input/output relationship, reflecting the proceduralcausal flow. Relationships for which no sufficient data, descriptive models, or other forms of knowledge are available were identified as knowledge gaps.