Simplified Analytical Procedure for Prediction of Fracture Damage in Composite Structures

Alpha STAR (Software Development/Engineering Consultant Company), and subcontractors from the University of California at Santa Barbara (UCSB), Clarkson University, and General Dynamics Boat division propose the development, demonstration and extensivevalidation of a simplified analytical procedure (SAPGEN) for naval joint design. SAPGEN will be developed to predict interlaminar failures, multi-site cracks initiation and propagation, establish design guidelines and inspection intervals, and evaluationof manufacturing flaws regarding part life.A Commercial version of Alpha STAR's, GENOA life prediction software is used in the SAPGEN code. Our extensive software development expertise contained in GENOA Commercialized life prediction software will be used, by identifying a convenient user-friendlysubset of this software, `SAPGEN'. The intent of the SAPGEN software is to provide the nucleus and foundation that will serve as an engineering design aid specific for naval composite structures and associated industrial practitioners.The SAPGEN code can accurately simulate structural damage, including hygral and thermal effects, under static, dynamic, impact, creep, stability, low and high cycle fatigue, and random power spectral density loads. The software uses material test data,and uncertainty at the material local level to simulate structure level damage initiation, growth, and propagation processes and determines the true global safety factors associated with each component design. Changes in structural load paths with damageprogression are accurately identified based on physics and material properties. Manufacturing processes variability, and anomalies (voids, defects, etc) can be accounted as part of life prediction simulation. Virtual structural health monitoring andnon-destructive evaluation (i.e. inspection) are monitored via exhausted energy release rate.SAPGEN will perform adhesively bonded joint analysis by: 1) automatic mesh generation, 2) material constituent analysis (MCA), 3) material uncertainty analysis (MUA), 4) progressive failure analysis (PFA), 5) damage minimization, and 6) time dependentreliability of. SAPGEN will be used to predict, under all operational conditions (temperature/thermal gradient, humidity, oxidative/corrosive agents): 1) constituent/ply mechanical properties, 2) property degradation by implementing the multifactorinteraction model, and 3) effects of bond line strength/thickness/voids on failure, 3) durability/reliability of a typical marine composite joint/structure, including determination of the failure mechanisms contribution to the critical damage events (crackinitiation/propagation), residual strength, sensitivity of joint design parameters (e.g. configuration, bond-thickness, ply-schedule) to the probability of failure. Figure 2- 1 shows the SAPGEN flow chart and compares the software damage predictioncapability against ABAQUS software. ASC's software development team adheres to ISO9000 processes, software control, and has established appropriate security firewalls in support of client's project needs. The benefits of the SAPGEN software modules, and the functionalities of each module is shown in Table 2-1.Some of these SAPGEN capabilities have been introduced in the developmental verification case studies. Most importantly the capabilities of the total GENOA software system can be drawn upon to progressively enhance later versions of the SAPGEN softwareduring Phase 2 and Phase 3 development as the user community becomes more familiar and accomplished with the initial release of SAPGEN.Table 2-1. Benefit of SAPGEN Module for the Design Build and Test of Navy Composite Joint ComponentsModule BenefitMaterial Constituent Analysis (MCA) Useful during the early phases of concept/product development in evaluating the impact of changes in Volume fraction involved in deciding on an appropriate fabrication approval or assessing environmental effect,degradation of material properties to environmental (moisture, thermal), manufacturing (defects, residual strains), etc.Material Uncertainty Analysis (MUA) Useful during the early phases of concept/product development in evaluating the impact of changes in Fiber architecture, Volume fraction, material mechanical properties on potential fracture damage involved.Progressive Failure Analysis (PFA) Ability to predict the factional contribution of failure mechanisms during the critical damage events (i.e. initiation, final failure), inspection intervals, under certain type of loading environmental conditions.effects of residual stress, and defects on structural integrity are introduced during manufacturing cool down process.Progressive Failure Optimization (PFO) Ability to perform parametric trade study of design parameters (volume fraction, ply angle, thickness) by minimizing the damage under certain types of loading environmental conditions.Probabilistic Progressive Failure Analysis (PPFA) Identification and sensitivity of progressive damage parameters, uncertainty evaluation of material strength to material parameters, determine sensitivities of failure modes to design parameters tofacilitate targeting design parameter changes that will be most effective in reducing probability of a given failure mode from occurring, and probability of failure.