William E. Wolfe

A STRAIN-ENERGY BASED FAILURE CRITERION FOR NON-LINEAR ANALYSIS OF COMPOSITE LAMINATES SUBJECTED TO BIAXIAL LOADING

The non-linear responses of a lamina under uniaxial longitudinal tension and compression, transverse tension and compression and shear loadings are used to predict the stress/strain response, failure onset and progression in composite laminates subjected to in-plane biaxial loading. A piecewise cubic spline interpolation scheme has been used to represent the basic material properties along the lamina material axes. A laminated plate theory that includes an iterative incremental constitutive law to account for the non-linear behavior of the laminae is combined with a strain-energy based failure criterion for orthotropic materials. Unloading of the failed laminae and subsequent failure progression of the laminate are included in the model. Results for failure onset and progression are presented for a wide variety of unidirectional and symmetric laminates under biaxial loading.

Evaluation of a dry FGD material as a flowable fill

Abstract Many flue gas desulfurization (FGD) materials have low unit weight and good shear strength characteristics and thus hold promise for flowable fill applications. This paper focuses on the potential of using spray dryer FGD ash in flowable fill as a replacement for conventional fly ash. Several design mixes were considered. The design mixes consisted of varying amounts of FGD, cement, lime, admixture, and water. The mixes were tested in the laboratory for flowability, unit weight, moisture content, unconfined compressive strength (UCS), erodibility, set time, penetration, and long-term strength characteristics. Tests were conducted for up to 90 days of curing. The FGD flowable fill without any additives was observed to be comparable to regular (normal set) flowable fill in terms of placeability, UCS, and ‘diggability’. FGD flowable fill with additives and admixtures compared favorably with the characteristics of conventional quick-set flowable fills.

Use of clean coal combustion by-products in highway repairs

Abstract A dry flue gas desulfurization (FGD) by-product was used to reconstruct the failed portion of a highway embankment. A wall was constructed through the failure plane to stop further slippage. To evaluate the suitability of FGD by-products in this type of project, the site of the repair was divided into three test sections. In the first section, the soil removed from the slide area was recompacted and replaced according to standard construction practices. In the second section, the embankment consisted of a field-compacted mixture of soil and FGD ash in approximately equal proportions. The third section was constructed of compacted FGD by-product. All three test sections were capped by a layer of compacted boiler ash or crushed stone to provide a temporary wearing surface. Measurements of slope movement as well as water quality and levels are being made at the site to evaluate long-term embankment performance. The completion of this experiment should lead to increased acceptance of FGD by-products in construction projects. Monetary savings will be realized in avoiding some of the disposal costs for the material, as well as in the reduced reliance on alternative engineering materials.

A strain-energy-based non-linear failure criterion: Comparison of numerical predictions and experimental observations for symmetric composite laminates

A strain-energy-based model to predict non-linear stress/strain response, failure onset and progression in composite laminates was presented by Wolfe and Butalia (Compos. Sci. Technol. 1998, 58, 1107). This paper focuses on some of the critical issues relating to the development of that model. Several of the assumptions made in the model are relaxed or modified. A variety of unidirectional and symmetric laminates are studied. A comparison of numerical results obtained from the model and published experimental data (Supplied by Soden, Kaddour and Hinton (Compos. Sci. Technol., in press) is presented for four different material systems. The strain energy based failure theory predictions agree very well with many of the experimental observations for the material systems investigated in this study.

Effects of recycled FGD liner material on water quality and macrophytes of constructed wetlands: A mesocosm experiment

We investigated the use of flue-gas-desulfurization (FGD) by-products from electric power plant wet scrubbers as liners in wetlands constructed to improve water quality. Mesocosm experiments were conducted over two consecutive growing seasons with different phosphorus loadings. Wetland mesocosms using FGD liners retained more total and soluble reactive phosphorus, with lower concentrations in the leachate (first year) and higher concentrations in the surface water (second year). Leachate was higher in conductivity (second year) and pH (both years) in lined mesocosms. Surface outflow did not reveal any significant difference in physicochemical characteristics between lined and unlined mesocosms. There was no significant difference in total biomass production of wetland plants between lined and unlined mesocosms although lower average stem lengths and fewer stems bearing flowers were observed in mesocosms with FGD liners. Potentially phytotoxic boron was significantly higher in the belowground biomass of plants grown in lined mesocosms with low phosphorus loading. A larger-scale, long-term wetland experiment close to full scale is recommended from this two-year mesocosm study to better predict the potentially positive and negative effects of using FGD by-products in constructed wetlands.

Flowable Fill Using Flue Gas Desulfurization Material

Flowable fills are an effective and practical alternative to commonly used compacted earth backfills. Flowable fill is a cementious material, commonly a blend of cement, fly ash, sand, and water, that does not require compaction, may be self-leveling at time of placement, may harden quickly within a few hours, and can be excavated in the future if need be. Many flue gas desulfurization (FGD) materials have low unit weight and good shear strength characteristics and thus hold promise for flowable fill applications. This paper focuses on the potential of using two types of FGD materials (spray dryer and wet fixated FGD material) in flowable fill as a replacement for conventional fly ash. Several design mixes were considered. The design mixes consisted of varying amounts of FGD material, cement, lime, and water. The mixes were tested in the laboratory for flowability, unit weight, moisture content, unconfined compressive strength, erodibility, set-time, penetration, and long-term strength characteristics. Tests were conducted for up to 90 d of curing. Without any additives, the FGD material was observed to be as good as a regular (normal set) flowable fill in terms of placeability, unconfined compressive strength, and diggability. FGD material flowable fill with additives and admixtures compares favorably with the characteristics of conventional quick set flowable fills.

The influence of freeze-thaw cycles on the compressive strength of stabilized FGD sludge

Abstract The effects of freeze-thaw cycling on the static compressive strength of samples of compacted, stabilized, wet flue desulfurization (FGD) by-products are reported. The results of laboratory tests show a clear relation between higher sample water contents and decreasing strength in the freeze-thaw cycling. In the samples tested, water contents ⩾40 wt% were characteristic of all the freeze-thaw specimens exhibiting low strengths. Lime content and curing time were also identified as having a marked influence on the durability of the FGD material. Samples can maintain good strength under freeze-thaw conditions if 5 wt% lime is added before compaction and the time from compaction to first freeze is at least 60 days.

Strain energy based failure criterion: Comparison of numerical predictions and experimental observations for symmetric composite laminates subjected to triaxial loading

An analytical model to predict the constitutive response, failure initiation and post-initial failure behavior of fibrous composites under triaxial loading has been developed based on a strain energy formulation. This paper highlights the means of developing several key parameters in the model and extends the model to include the effects of in-plane thermal residual stresses accumulated during the curing of composite laminates. The derivations of a set of consistent model input parameters for several composite material systems are described. A series of comparative stress-strain curves and failure envelopes are provided comparing model predictions to published experimental data. The strain energy based failure model is found to provide good agreement with the experimental observations studied in this work.

A strain energy based failure criterion for nonlinear analysis of composite laminates subjected to triaxial loading

A new strain energy based failure model is developed for fibrous composite laminates under multi-axial loadings, taking into account the effect of hydrostatic stress. A failure mode dependent exponential stiffness reduction model is used to predict material response beyond the initial failure. Predicted mechanical responses and failure envelopes are presented for the 12 benchmark test cases of Part A of the Second World Wide Failure Exercise. The cases cover a wide variety of isotropic, unidirectional and multidirectional laminates under combined in-plane, out-of-plane and triaxial loadings. Both stress–strain curves and the complete failure envelopes were successfully predicted. In some instances, the failure envelopes were open. The predictions together with suitable adjustment of certain parameters are compared with test data in Part B of the Second World Wide Failure Exercise, to be published in Journal of Composite Materials.

Variational formulation and finite element implementation of Pagano's theory of laminated plates /

SUMMARY Paganos theory of laminated composites is restated as a self-adjoint system of coupled equations. Consistent boundary operators are identified and a general variational principle, allowing for non-homogeneous boundary conditions as well as possible internal discontinuities is stated. Possible extensions to relax requirements of differentiability of various field variable are discussed. Specializations, restricting the variables to identically satisfy one or more of the field and/or boundary conditions, serve to reduce the number of free field variables. One such specialization is implemented in a finite element computer program used to solve several example problems of stresses in free-edge tensile specimens.