The aim of the present paper was to study the feasibility of using olive oil mill effluents (OMEs) as a substrate in biodegradable polymer production. OMEs were anaerobically fermented to obtain ...volatile fatty acids (VFAs), which are the most highly used substrate for polyhydroxyalkanotes (PHAs) production. The anaerobic fermentation step was studied both without pretreatment and with different pretreatments (i.e., centrifugation, bentonite addition, and bentonite addition followed by centrifugation) and at various concentrations (28.5, 36.7 and 70.4
g
COD
L
−1). During fermentation, VFA concentration was determined (7–16
g
COD
L
−1) as well as the corresponding yield with respect to initial COD (22–44%). At all initial concentrations, centrifugation pretreatment (with or without previous addition of bentonite) significantly increased the final VFA concentration and yield, whereas the addition of bentonite alone had no influence. Moreover, centrifugation pretreatment led to a different acid distribution, which affected the hydroxyvalerate (HV) content within the obtained copolymer poly
β-(hydroxybutyrate-hydroxyvalerate) P(HB-HV). OMEs were tested for PHA production by using a mixed culture from an aerobic SBR. Centrifuged OMEs, both with or without fermentation, were tested. PHAs were produced from both matrices, but with fermented OMEs PHA production was much higher, because of the higher VFA concentration. The initial specific rate of PHA production obtained with fermented OMEs was approximately 420
mg COD
g
COD
−1
h
−1 and the maximum HV content within the copolymer was about 11% (on a molar basis). The HV monomer was produced only until propionic acid remained present in the medium.
► Single angular particle impacts on Al6061-T6 were modeled using the SPH method. ► The model allows for simulation of crater formation, chip removal and material pile up. ► The Cowper–Symonds strain ...rate equation performs better than the Johnson–Cook. ► The study has implications for solid particle erosion due to multiple impacts.
Smoothed particle hydrodynamics (SPH) was used to simulate the impact of single angular particles on Al6061-T6 targets, and the implications for solid particle erosion were discussed. The results of the simulations were verified by comparison to measurements obtained from impact experiments performed using a gas gun which was specifically designed to accelerate angular particles without disturbing their orientation with respect to the target. Both the simulations and the experiments showed that an increase in impact angle and initial orientation of the particle altered the deformation mechanism of the target material, as noted by other investigators. For impact angles close to normal, a significant amount of target material was extruded and piled up at the edge of the impact craters, due to the limited strain hardening of Al6061-T6. However, for certain combinations of incident parameters, the particle machined the surface and a chip was removed. With appropriate constitutive and failure parameters, SPH was demonstrated to be suitable for simulating all of the relevant damage phenomena, including crater formation, material pile-up and chip separation.
The damage to materials resulting from the impact of solid particles depends on their velocity, shape and size. In contrast to spherical particles, since granular particles typically are highly ...irregular in shape, they cannot be idealized by a single two dimensional geometry in numerical models of impact damage. In this work, a methodology was presented for generating realistic particle geometries based on measurements of the distribution of particle surface area, circular diameter, sphericity and thickness for a sample of 150μm nominal diameter angular aluminum oxide powder. The methodology was used in a coupled smoothed particle hydrodynamics (SPH)/finite element (FE) model to simulate 124 non-overlapping particle impacts on an Al6061-T6 target, both at normal and oblique incidence. It was shown that the simulated particles produced distributions of crater and crater lip dimensions that agreed well with those measured from particle blasting experiments. A number of different material removal mechanisms were identified from the simulations, and discussed in the context of previously observed solid particle erosion mechanisms. The companion paper Takaffoli and Papini, in preparation 1 utilizes the methodology to simulate solid particle erosion processes involving overlapping craters.
► A methodology to generate 3D representative models of erodent particles was presented. ► Non-overlapping impact of modeled particles was studied using a numerical model. ► The predicted size of craters and pile ups compared well with those measured. ► Different impact mechanisms identified from the simulation were discussed.
Abrasive water jet (AWJ) machining of delicate materials is difficult due to the large pressures that commonly result in large-scale chipping and other target damage. The damage occurs mostly during ...the initial piercing operations when the jet flow creates a large stagnation pressure at the jet to surface interface at the bottom of blind holes. This paper examined the parameters that affect target damage during piercing operations in borosilicate glass. The effects of stand-off distance (SOD), dwell time and pressure for three nozzles sizes were compared. A novel aspect of the study is the use of a prototype 254μm micro-abrasive waterjet machining (μAWJM) nozzle. The results of a parametric analysis identified machining configurations that resulted in the reduction of chipping and hole size, and an improved hole circularity. This paper also proposed and assessed two methods for the reduction of exit pierce chipping using the μAWJM nozzle. A finite element analysis showed that the use of stacked borosilicate glass plates reduced the exit stresses associated with through piercing, thus reducing the amount of exit hole chipping. An μAWJM/AJM (micro-abrasive waterjet machining/abrasive jet machining) hybrid operation was also shown to considerably reduce exit chipping and exit hole size.
The solid particle erosion of a spherical alumina particle-reinforced epoxy matrix composite was investigated. Three dimensionless parameters were demonstrated to play key roles in the erosion ...resistance: r1, the ratio of the abrasive to reinforcement particle size; r2, the ratio of the abrasive particle size to the average edge-to-edge distance between reinforcements; and r3, the ratio of the abrasive particle kinetic energy to a threshold kinetic energy. At perpendicular incidence, modest improvements in erosion resistance could be obtained at intermediate r2 values (1 < r2 < 3) when r1 was intermediate (0.2 < r1 < 0.35). At oblique incidence, the erosion resistance of the composites was significantly higher than the neat epoxy in all cases. The results may have important implications for the design of polymeric composite coatings.
•Three new dimensionless parameters were demonstrated to control the erosion rate.•Dominant erosion mechanisms were shown to depend on the dimensionless parameters.•At oblique incidence, adding hard reinforcements improved the erosion resistance.•At perpendicular incidence, sub-channeling and reinforcement fracture were the main mechanisms.
Particle embedment may occur in erosion testing, abrasive jet machining, blast cleaning and other industrial processes in which high speed impact of particles on relatively ductile targets occurs. It ...may strongly affect erosion rates, and lead to undesirable changes in surface roughness. Three-dimensional smoothed particle hydrodynamics (SPH) simulations were used to simulate particle embedment when 219.2µm and 362.9µm angular silicon carbide particles impacted a strain and strain rate hardening 6061-T6 aluminum alloy target under various process conditions. The models were assessed by comparison with measured embedment. Analysis of the results showed the following: (i) once the value of the effective friction coefficient between the substrate and the abrasive was determined by comparing predicted and measured embedment at one set of process conditions (particle velocity, size, angle of attack), the same friction coefficient could be used in models of all other combinations of process conditions to correctly predict embedment. (ii) Consistent with a previous simplified rigid-plastic analysis of idealized rhomboid particles impacting a polymer target, the static frictional force occurring after the maximum depth has been reached, the particle orientation and the impact angle all strongly affected embedment. Unlike the previous simplified model, the present model considered local strain rate and strain hardening, making it applicable for ductile metal targets. (iii) Consistent with some, but not all, reports in the literature, embedment at a given velocity increased with particle size. (iv) For a given particle size, embedment increased with incident velocity. (v) A critical minimum velocity below which embedment would not occur was predicted. The trends were discussed in terms of embedment mechanisms and particle impact kinematics. Overall, the work demonstrates that SPH methods can be used to provide insight into complex solid particle erosion phenomena.
•Particles embedment was simulated and compared to experiments.•A single friction coefficient was used to predict embedment at all conditions.•Embedment increased with particle size and incident velocity, independently.•Embedment depended strongly on percentage of oriented particles.•A threshold below which no embedment occurred was predicted.
A culture of Arthrobacter sp. was tested for its ability to sorb copper, cadmium, and iron ions, and chemical modeling of experimental data was used to interpret the mechanism of biosorption. The ...purpose of the initial phase was to clarify the nature and concentration of active acidic sites on cell wall with the aid of potentiometric titration of an aqueous cellular suspension and IR analysis of the lyophilized biomass in solid phase. The experimental results showed that the cell wall probably has at least two weakly acidic sites. In the second part of the experimental work Arthrobacter sp. was suspended in the presence of copper, cadmium, and iron ion solutions at different equilibrium pH values. Adsorption isotherms were obtained by using an original procedure defined as the “subsequent additions method” (SAM). The results showed a strong influence of pH, especially over pH 5. A chemical model based on a possible set of reactions between ions in solution and the biomass has been developed. Mechanistic modeling revealed the complexity of the metal biosorption phenomenon and the need to consider different biosorption mechanisms. Up to pH 5 experimental data at different equilibrium pH values can be described using a model which takes into account only two mechanisms (ion exchange and complexation). Over pH 5 other mechanisms (probably precipitation or coprecipitation on cell wall surface) should be considered.
In the accompanying paper (M. Takaffoli, M. Papini, Numerical simulation of solid particle impacts on Al6061-T6 Part I: Three dimensional representation of angular particles), it was demonstrated ...that realistic 3D models of angular particles could be generated and used with a smoothed particle hydrodynamics model to simulate the damage done to an Al6061-T6 target due to many non-overlapping particle impacts. In this paper, the same methodology was used to simulate overlapping impacts, and thus the material removal mechanisms associated with the solid particle erosion of this material. The evolution of the topography of the blasted surface was simulated, and the surface ripple patterns that typically form during the erosion of aluminum alloys were observed. The predicted volumetric erosion rates at different impact angles were, on average, within 7% of those measured in erosion experiments. An investigation of the simulated trajectory of the impacting particles revealed the cooperative contribution of overlapping impacts to material loss, and solid particle erosion mechanisms such as the micromachining of chips, the ploughing of craters, and the formation, forging and knocking off of crater lips. The results indicate that numerical simulation of the solid particle erosion of ductile metals by realistic angular particles is possible.
► Overlapping impacts of 3D irregular shaped particles were studied. ► A coupled finite element/smoothed particle hydrodynamics model was developed. ► Predicted erosion rates compared well with those obtained using blasting tests. ► Cooperative effects of multiple impacts on material removal were discussed.
Delamination is a common defect when abrasive waterjet (AWJ) cutting composite laminates. This paper presents experimental and numerical results used to characterize delamination when AWJ cutting a ...carbon-fiber/epoxy laminate. A fluid-structure interaction model was used to simulate the AWJ cutting. The structural domain used cohesive zone modeling to predict delamination along the ply interfaces. The numerical results showed that cutting delamination of the carbon-fiber/epoxy was primarily dependent on the normal interlaminar stress, with relatively large damage zones occurring ahead of the cutting front. This trend was also observed in X-ray micro-tomographs of an AWJ cut. To distinguish between side-wall and cutting-front forces, the loading generated by the jet was measured using a strain gage. This showed that the loads applied to the cutting front were larger than those generated on the side walls, and thus the likelihood of delamination was greater on the cutting front. The amount of delamination during AWJ cutting was measured using a moisture uptake methodology that was implemented with a six-factor (pressure, stand-off distance, abrasive flow rate, traverse speed, mixing-tube size, and fiber orientation) Taguchi experimental design. The trends evident in these data were consistent with the extent of delamination predicted by the numerical models, and show that traverse speed, abrasive flow rate, and mixing tube size had the most significant effect on delamination.
Surface roughness is a valuable metric when assessing abrasive waterjet machining (AWJM) cut quality. This paper presents 2D and 3D models capable of predicting the surface roughness during abrasive ...waterjet (AWJ) trimming of composite substrates. The composites used were a carbon-fiber laminate with an epoxy resin and a random oriented carbon-fiber/vinyl ester. The models were based on an earlier rigid-plastic erosive particle indentation model capable of predicting crater sizes using the particle impact and substrate properties. In the 2D model, single particle impact craters were aligned to form multi-particle impact profiles that were iteratively superimposed until a steady-state surface roughness was achieved. The 3D model generated conical craters that were individually superimposed until a steady-state surface roughness was achieved. The models were capable of predicting the surface roughness with an average error of 10% and 16%, for the 2D and 3D models, respectively. The models show that the surface roughness decreased with an increase in particle velocity, a decrease in kerf taper, and an increase in the dynamic hardness of the target.
•An analytical 2D and 3D surface roughness model for AWJM of composite materials is proposed.•The 2D and 3D models are shown to have an average error of 10% and 16%, respectively.•The models are based on a fundamental rigid-plastic impact model for single particle erosion and superposition of craters.•A sensitivity analysis provides extended insight on the mechanisms of surface roughness when AWJM.
