A Multiscale Nonlocal Progressive Damage Model for Composite Materials

In this paper, the advantages of a nonlocal progressive damage formulation are described and demonstrated. An approximation of the nonlocal formulation was implemented coupled with the MAT162 composite damage model as a User defined material model in the LS DYNA environment. A comparison of the local model and the nonlocal model is simulated for an 8-ply laminate under tension is carried for increasing mesh densities. The results show the regularization achieved by nonlocal models by providing mesh independent results

Pharmacokinetics of oral mycophenolate mofetil (MMF) in patients with lupus nephritis with a special reference to the measurement of free MPA and saliva MPA.

Mycophenolate Mofetil (MMF), the immunosuppressive agent, is commonly used to treat renal transplant patients and patients with other autoimmune diseases such as Systemic Lupus Erythematosus (SLE). Due to the high inter-dose, inter-patient variability in drug exposure, therapeutic drug monitoring (TDM) has proved extremely beneficial in individualizing the MMF therapy. Measurement of Mycophenolic Acid (MPA) area under the curve (AUC0-12 hr) involves collection of multiple blood specimens, over 12 hours. Objectives: (i) To establish the pharmacokinetics of MMF in patients with lupus nephritis (ii) To develop a limited sampling strategy (LSS) for the estimation of MPA AUC0-12 hr. (iii) To determine if any correlation between free MPA in plasma and saliva MPA concentration. Methods: Plasma specimens from 30 patients with lupus nephritis were prospectively collected at the respective time points: trough (prior to MMF dose), then at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8 and 12 hours after patients had taken MMF. Total MPA AUC 0-12 hr was estimated using high performance liquid chromatography (HPLC with UV detection). Saliva and free MPA concentrations were collected at 1 hour post-dose, measured and their correlation was compared. Limited sampling strategies with acceptable correlation coefficients (R2), bias and precision were developed by stepwise multiple regression analysis. The predictive performance of the LSS was validated using bootstrap validation. Pharmacokinetic parameters were analysed using Pmetrics software for R. 14 Results: The observed MPA AUC0-12 hr ranged from 19.52 to 67.67 mg.h/L with a mean of 45.12 mg.h/L. The mean Cmax and Tmax were 16.703 mg.h/L and 1.08 h respectively. The mean dose per kg body weight of MMF prescribed was 26.47 mg/kg. The best LSS model included concentrations at time points 0, 1, 2 and 4 (C0, C1, C2, C4) (multiple R2=0.926). The final model validated post bootstrap is as follows: MPA AUC0-12 hr= 12.3376+ (2.9013XC0) + (0.8305XC1) + (0.7945XC2) + (4.5156XC4). Calculated bias and imprecision for the LSS were -0.13 and 7.09 % respectively. The observed correlation between free MPA in plasma and saliva MPA was poor overall (r=0.085, p>0.05). However good correlation (r= 0.790, p=0.02) was observed in the low albumin group (n=8). Conclusion: This study has, for the first time, described the pharmacokinetics of MMF in adult Indian patients with lupus nephritis and the developed 4 point LSS is an accurate measure of the total 12-hour MPA AUC0-12 hr with favourable bias and precision

Progressive Failure Analysis of composite Materials using the Puck Failure Criteria

Fiber reinforced composites have been used in various engineering structures and applications especially in naval, automotive, aeronautical and sports industries. These composite materials generally exhibit brittle damage behavior. The anisotropy in the material and different kinds of failure mechanisms make it difficult to accurately characterize the behavior of composite materials. The present work aims to verify and apply the Puck Failure Criteria using the commercially available finite element package ABAQUS by writing a user-material subroutine in FORTRAN. The model is implemented with different post failure degradation schemes. In the present work, the progressive failure on composite materials in analyzed using the Puck failure criteria to detect damage initiation. The ABAQUS user defined material subroutine UMAT was developed to apply the failure criteria and degradation models. The progressive failure analysis of a single lamina of a composite material is carried out on an open hole specimen under uniaxial tension. A partial discount method and a gradual stiffness degradation method is implemented and the results using these degradation models are compared. The damage initiation and progression obtained from the proposed model is compared with the observed experimental results and the digital image correlation data. This model was then used for the progressive failure analysis of a composite laminate with a central hole loaded in inplane tension with different stacking sequences and compared with the results obtained from literature. From the results, it can be seen that the Puck failure hypothesis is a robust and versatile criteria which can be used for the progressive failure analysis of continuous fiber unidirectional composite laminates

Studies of Damage Tolerance in Automated Fiber Placement Based Heterogeneous Meso-Architectured Carbon/ Epoxy Composite Laminates.

Traditional unidirectional (UD) carbon fiber-reinforced polymer matrix composites manufactured via automated fiber placement (AFP) are widely used in aerospace structures. While heterogeneous at the micro-scale, these materials are homogeneous at the meso-scale (ply-scale). The major limitation is its limited toughness, poor damage tolerance/impact resistance capability and the inability to sufficiently redistribute stresses, resulting in strength-toughness tradeoffs, making them susceptible to impact damage. From previous studies, there is an understanding that fiber architecture has a first order effect on the damage tolerance. Introducing new discontinuous/heterogeneous meso-scale architectures, through an optimal merger of material and structure, can result in unprecedented property improvements due to multiple interacting deformation mechanisms as demonstrated in biological/biomimetic architected materials. Interestingly, controlling/inducing multiple deformation/failure mechanisms via spatial distribution of in-plane anisotropy (i.e., heterogeneity in fiber orientations) and boundaries / interfaces is largely unexplored. In recent years, a specialized AFP layup procedure was introduced to mimic a woven-like architecture using UD prepreg tows. In this modified procedure, tows are intentionally skipped during placement leaving gaps. These gaps are filled in the subsequent passes to produce pseudo-woven meso-architectured composites (MAC). The unique architecture is macroscopically heterogeneous with discontinuous and spatially varying fiber orientations both in-plane and through thickness resulting in multiple interfaces and an expanded design space. This dissertation explores the incorporation of MAC laminates manufactured using AFP to enhance the damage tolerance of unidirectional carbon fiber reinforced polymer composites. An extensive experimental study has been carried out on hybrid carbon fiber reinforced laminates (consisting of MAC and traditional UD sub-laminates) compared against a baseline traditional unidirectional quasi-isotropic control laminate under high velocity impacts of 250-400ft/s, low velocity impacts of 15-55 J, open hole tension and open hole compression. C-scans and digital image correlation techniques are employed to better understand the experimental response. The hybrid MAC laminates demonstrate a significant 45% reduction in back-face surface damage, 19.5% less back face deflection and an 18% increase in penetration velocity when compared to quasi-isotropic control laminate under high velocity impacts. Under a low velocity impact, the hybrid laminate configurations exhibit increased damage resistance with up to 37% higher critical delamination load and increased damage tolerance with 26% higher residual compressive strength after an impact of 55 J compared to control laminate. Additionally, the hybrid MAC laminates demonstrate a 7% increase in OHT strength and up to a 16% reduction in strains near the open hole while the OHC response is found to be similar. To better understand the operating mechanisms in MACs, a python script is developed to mimic the AFP layup procedure to determine the spatial variations in the fiber angle and stacking sequence and determine the representative unit cell. Furthermore, finite element models are developed to better understand the damage propagation mechanisms in these complex heterogeneous materials. The studies demonstrate that improved impact performance in MACs is due to crack deflection, damage diffusion and stress redistribution mechanisms induced by the heterogeneous composite architecture and provides insights into the fundamental deformation and failure mechanisms during impact onto these complex

Detailed Bathymetric Surveys in the Central Indian Basin

Over 420,000 line kilometers of echo-sounding data was collected in the Central Indian Basin. This data was digitized, merged with navigation data and a detailed bathymetric map of the Basin was prepared. The Basin can be broadly classified into three regions as high relief area, medium relief area and plain area represented by western, eastern and central portions of the Basin, respectively. The bathymetric map prepared from this survey is the first of its kind for this region and will in the future be used as a base by navigators and researchers

Multibeam echosounder pseudo sidescan images as a tool for manganese nodule exploration

Deep ocean floor is the storehouse of vast quantities of mineral resources and manganese nodules are one of the important resources. The method of semi quantitative evaluation of nodule resource estimation using the rms (root mean square) backscatter amplitude gain values from a multibean echosounding system is presented. Normally, the echosounding system provide information only about the water depths whereas the sidescan images can provide information on the large and small scale roughness and seafloor composition in terms of texture etc. Present day multibeam sonars can produce sidescan images of the surveyed region. The multibeam system- Hydrosweep on Indian Research ship ORV Sagar Kanya doesn't provide the sidescan images, but only gives the rms amplitude values for each of the 59 pre formed beams. In this report, the rms amplitude values are utilised to generate pseudo sidescan images of the seafloor. An area of about 6600 km sup(2) in the Central Indian Basin was mapped using the Hydrosweep system and depth contour and pseudo sidescan images of the area have been generated. A comparison of nodule abundance values with the sidescan image shows that, the light gray patches show high manganese abundance values (more than 10 kg/m sup(2)) where as the dark tones on the sidescan images correspond to low abundance values (up to 4 kg/m sup(2)). As multibeam mapping can be carried out at normal ship speeds, the pseudo sidescan images can be a useful and inexpensive tools for manganese nodule exploration

A note on the morphology of Kainan Maru Seamount, East Antarctica

Kainan Maru Seamount lies off the northern end of the Gunnerus Ridgealong the margin of East Antarctica. The seamount is separated from theGunnerus Ridge by only about 15 km. Detailed Hydrosweep multibeamsurveys of the seamount have shown that the seamount rises over3,500 m above the surrounding seafloor, has an oval shape about 60 kmwide and 120 km long, and has a gently sloping summit. The northernand eastern sides of the seamount are steeper than the southern andwestern sides. Many erosional channels cut the northern and easternflanks of the seamount, whereas the western side shows evidence oflarge sediment slides and is more gently sloping. The morphology of theseamount, as observed in the bathymetry and satellite gravity data,suggests that Kainan Maru Seamount may be a detached piece of theGunnerus Ridge that rotated clockwise away from the ridge during therifting of Gondwana in this area