Search

Failure of stiffened panels under compression is preceded by buckling of their skin and hence is affected by the presence of out-of-plane stresses. One of the promising methods of preventing premature delamination is stitching. The present paper discusses the effect of such stitching on compression behavior of blade-stiffened panels that were fabricated from plain weave AS4/3501-6 through resin film infusion process. Kevlar 29 yarn was used at a stitch density of 9.92 stitches per cm2. Some of the panels were damaged by drop-weight impact before compression testing. For comparison purposes unstitched panels with the same materials and dimensions were also tested under the same loading conditions. Stitching resulted in a 10% improvement in strength in the absence of any intentional damage. The beneficial effect of stitching was most obvious when the panels were impacted on a flange: a 50% improvement was observed in post-impact strength. However, stitching could not prevent stiffener from failure when impacted directly. Thus stitching had no beneficial effect when impact occurred on a stiffener. A buckling and post-buckling analysis was carried out using 3-D shell elements on the Abaqus. Predictions were in fairly good agreement with the experimental data.

The vacuum assisted resin transfer molding (VARTM) of sandwich panels may be facilitated by using high permeability layers over the skins or adding grooves in the surfaces of the core. The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. Before comparison, each method is optimized through simulations. The panel geometry and the injection pressure are held constant. The design parameters are the number of high permeability layers, and the number and size of grooves. The optimized processes are finally compared with each other in terms of the aforementioned cost and time. Meanwhile, the sensitivities of several important parameters in the cost model to the optimal result are studied.

Much research has been conducted to understand the damage tolerance behavior of polymer matrix composites. As a result, a fair amount of data is available together with a number of analytical models. However, there are so many parameters involved that the development of a generic model is rather difficult. The present paper proposes a decision support system, which can overcome such difficulty. In the information system, a list of possible parameters is generated and used as input. The output contains compression strength after impact, dent depth and damage area as well as literature references, raw data, tables, and plots. The information system is constituted in a relational database environment and expert system technology is incorporated so that low confidence input can be captured in order to report best matching cases. Parametric studies are also made available to determine the effect of each design parameter on the damage tolerance behavior. Case examples are included to demonstrate the practical use of the software for both data retrieval and similarity studies.

In resin transfer molding (RTM), the formation of air voids within fiber preform depends on the flow rate and surface tension of the resin during mold filling. The resin velocity in regions between fiber tows is mostly controlled by the induced pressure gradient whereas the resin flow within each fiber tow depends more on the capillary pressure. As these two flows compete in their advancement, the size and location of air voids vary from point to point. Capillary number, defined as the ratio of the viscous force to the capillary force, has been found through experiments to be the critical parameter controlling the type of microvoids. The present paper proposes a model that can account for the dependence of the size and quantity of air voids on the capillary number. At low capillary numbers, the soaking flow within individual fiber tows dominates mold filling, and hence voids are more likely to form between fiber tows. At high capillary numbers, the situation is reversed so that the inter-fiber-tow flow outruns the intra-fiber-tow flow resulting in voids within fiber tows. At an optimum capillary number, the two flows are comparable, minimizing the possibility of void formation. The proposed model can quantify the effect of capillary number on void formation. The model has been validated through experiments.

A process specification language is being developed for virtual manufacturing that provides a structured portable definition of a given manufacturing process as well as the ability to specify the temporal relationships between individual operation steps that compose a process. Based on the concepts embodied in markup languages such as HTML, SGML and XML, a portable process definition structure is defined. This structure provides a template from which virtual process specifications can be created. Subsequently, these structures can be exchanged between development environments for virtual process engineering and the actualized manufacturing facilities where processes are implemented. In addition, dependencies in time between the operation steps of a process such as common start times and operation serialization can be represented to allow for a complete specification of temporal behavior of a given manufacturing process. By providing this explicit mechanism for representing temporal constraints, a virtual manufacturing process can be viewed and utilized both in a localized application on a single virtual factory floor as well as distributed across multiple, interlinked virtual environments.

In order to address the computational costs of modeling and analyzing manufacturing processes, a novel approach to virtual manufacturing process engineering using generic modular operations is presented. Relying on a state based representation of operation control for a simplified virtual manufacturing workcell, the valid states for each sequence of generic modular operations are aggregated and both operation state and processing constraints applied to specify the subtasks required to complete each step in a product’s process plan. By adopting this state based control approach, virtual process engineering provides a direct mechanism to map virtual process representations onto actualized processes. Using these generic modular operations and their temporal and processing dependencies, the computationally complex elements of virtual manufacturing process simulation can be directly identified and an architecture for virtual process development specified. Examples from both machining and assembly processes are provided.

In order to reduce assembly complexity and enhance the performance of structural elements utilized in transportation systems, a novel approach is presented that uses integral fit joints in the assembly of fiber-reinforced composite structural elements. While the application of composite materials in transportation structures is not new or unique, their use coupled with integral fit joint designs affords a multi-magnitude reduction in the number of components required to assemble transportation systems. Essential to this effort is the need to effectively model and analyze the composite integral fit joint specifically focused on assembly. This paper introduces pertinent issues in the design and assembly of transportation systems, the assembly of their structural joints, and defines assembly models and analysis methods for composite integral fit (CIF) joints.

The development approach embodied in design for assembly (DFA) has been demonstrated effectively in different industrial sectors and through the design of a multitude of products. However, little effort has been applied to improving development methods for the assembly operations and processes used to fabricate these products. If the benefits of concurrent engineering are to be fully realized, a more holistic approach to unifying a product’s design with development of its assembly processes is needed. This paper provides a description of our approach to establishing an environment for coordinated product and assembly process development. The steps in a product’s development cycle are introduced and the concepts of design for assembly and concurrent engineering defined. Using DFA methods as a motivation, an approach to assembly process development is derived. Referred to as Systematic Assembly Process Development (S-APD), assembly processes are defined and analyzed by using standardized generic assembly operations. To address problems created by using concurrent engineering in product/process development, two mechanisms are described. Since the focus of developing a product (i.e. how well does it perform and cost) differs from developing its assembly processes (i.e. making products at the necessary volumes), the concept of an interface reference context is introduced as a coordination mechanism and applied to development of unmanned composite low-cost aircraft. Moreover, in identifying which elements of the design are to be assembled with a specific set of production technologies, a synchronous thread is instantiated to link product and assembly process development efforts in a temporal context. Different approaches are reviewed to resolve potential conflicts related to concurrency effects generated during simultaneous product and assembly process development.

The demand for the better quality products with shorter lead-time and lower life-cycle cost forces the manufacturing enterprises all around the world to optimize their production strategies from both enterprise engineering and enterprise operation respectively. This paper addresses the architectural issue of applying the Concurrent Engineering (CE) approach in the composite manufacturing area. It first discussed briefly the characteristics of composite manufacturing process to examine the feasibility and possibility of applying the CE approach to improve its process productivity and product quality. Then the functional requirements for a concurrent engineering system for composites (CESC) were defined from both operational and architectural points of view. Finally, the integrated infrastructure based system architectures for the CESC were presented in accordance with the physical system requirements, and so were the associated and currently conducted R&D focuses for the system.

Concurrent with the use of tailored materials for specific applications has been the understanding that a product’s design has a significant and measurable effect on manufacturing process cycle times and unit production costs. In order to reliably manufacture and assemble aircraft structures fabricated from composite materials on a cost-effective basis, an environment for virtual assembly production analysis is being developed. Within this environment, members of an aircraft’s integrated product development team can rapidly assess the impact of design decisions on individual assembly operations and overall aircraft assembly in a virtual manufacturing context. Effects related to joint design and component matings are measured based on force and process conditions as well as the types of tooling required for final assembly. By evaluating assembly production impacts early during product design, the costly design-manufacture-redesign cycle is redefined and recast based on the realities of manufacturing process constraints.

This paper has first examined the manufacturing process of composites and the feasibility to apply concurrent engineering idea to improve its productivity. Then the key components including their roles played in the manufacturing process of composites and the requirements to the CE system for composites have been properly identified and analysed. Based on these requirements, an infrastructure based system architecture for the CE system was designed. Finally, the scheme to implement a CE system for composites was presented.