In global organisation, collaboration within distributed team is a crucial issue. Many companies are organizing communities of practice to improve experience sharing. These communities are mediated by collaborative platforms. Among collaborative functionalities, forum are expected to support distant asynchronous collaboration. But few studies show the effectiveness of this tool to support effective collaboration in the context of engineering design activity. The paper study the interactions through forums of two Virtual communities of practices of experts within R&D teams of international company. A coding scheme is proposed to analyze and characterize the online interactions. Through these two case studies, we demonstrate that a forum can support asynchronous argumentative activities and thus enhance global collaboration in distributed R&D organizations. The proposed characterization of collaboration can be a step to dynamic evaluation team interaction.