Examinando por Autor "Salazar, Alicia"

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Aging effects on the structural integrity of carboxyl terminated polybutadiene propellants
(Elsevier, 2025-04) Martínez, Mario; López, Raúl; Rodríguez, Jesús; Salazar, Alicia
Structural integrity of composite solid propellants (CSPs) is one of the main concerns when considering the performance of CSP motors. The development of cracks in the propellant’s grain, caused by aging during the service life of the motor, is the main reason for its catastrophic failure. In addition, the fracture characterization of these viscoelastic and highly filled materials is not fully solved yet and hardly addressed for aged CSP. This manuscript presents a broad and comprehensive study on the fracture behavior of aged CSPs, where Schapery’s viscoelastic fracture mechanics (VEFM) methodology is used to effectively characterize the fracture behavior of a composite solid propellant with carboxyl-terminated polybutadiene (CTPB) binder. For that, stress relaxation, fracture and tensile tests have been performed on non-aged and aged CSP. Three different accelerated aging methods were employed (mechanical, thermal and ozone) that are related to the phenomena that deteriorate the material during the lifespan of the motor. Two main contributions are derived from this work. The first one is the understanding of the fracture processes developed in aged CSP, under different types of aging. The second most relevant contribution is that the cohesive stress, as the fracture parameter inferred from the VEFM approach, is observed to be correlated to the dewetting stress, a material measurable parameter. The results have potential implications for the design and longevity of future solid rocket propellants
Effect of the orientation on the fatigue crack growth of polyamide 12 manufactured by selective laser sintering
(EMERALD GROUP PUBLISHING LTD, 2019-01-07) Cano, Alberto Jesús; Salazar, Alicia; Rodríguez, Jesús
Purpose – Polyamide 12 (PA12) properties meet specific requirements for various applications in the automotive and aerospace industries. Bulk specimens made of PA12 and processed via the additive manufacturing technique such as selective laser sintering (SLS) present a layered structure. In case of structural applications, the fatigue performance of SLS PA12 parts is of vital importance and fatigue response studies in these type of materials are still scarce. Therefore, the purpose of this paper is to analyse the effect of the applied load orientation on the fatigue crack propagation behaviour of the layered structure of SLS PA12. Design/methodology/approach – With the aim of understanding the effect of the applied load with respect to the layer orientation on the fatigue crack growth of SLS PA12, fatigue crack growth tests were carried out at two orientations. The specimens called PARA were orientated in such a way that the applied force direction belongs to the layer plane while in the group called PERP, the tensile force direction is coincident with the build direction, that is, perpendicular to the slice. Besides, special attention has been paid to the analysis of the fracture surfaces of the specimens, linking the micromechanisms of failure with the microstructure of the material. Findings – The SLS PA12 specimens tested with the load applied parallel to the layered structure show a little better fatigue response than those tested at perpendicular orientation. The fracture surfaces of the specimens tested at perpendicular orientation are slightly smoother than those tested at parallel orientation. Crazes are the main micromechanism of failure with a crater size of 50 microns, which coincide with the spherulite size. This indicates that the void nucleation of the crazes takes places between lamellae inside the spherulites, and consequently, the craze growth and rupture occurs mainly in a transspherulitic mode. Originality/value – PA12 parts manufactured via SLS are becoming more valuable in structural elements in the automative and aeronautical fields. In such applications, fatigue performance is vital for design. Fatigue studies are scarce in literature and even more when dealing with fatigue crack growth behaviour. The value of this work is the analysis of the fatigue crack growth response of these materials taking into account the anisotropic microstructure and to get a better understanding, this behaviour is explained taking into account the micromechanisms of failure and the microstructure of the material.
Evaluation of different crack driving forces for describing the fatigue crack growth behaviour of PET-G
(ELSEVIER, 2017-10-21) Cano, Alberto Jesús; Salazar, Alicia; Rodríguez, Jesús
To predict the fatigue crack growth in full-scale components made of polymeric materials, a methodology to transfer laboratory crack-growth data to structures is needed. This requires the similitude hypothesis to be applicable using a valid crack driving force, which allows the description of the R-ratio effect on the crack growth behavior. Whereas in metals it is common to use the range in the applied stress intensity factor, ΔK, as the crack driving force, in polymeric materials and composites the use of the energy release rate G has been considered and Δ G has been proposed as the crack driving force to ensure the similitude principle. Therefore, the aim of this paper is to assess the validity of Δ G as a proper crack driving force and to explore the way of practical application in an amorphous thermoplastic copolyester Polyethylene terephthalate glycol (PET-G).
Evaluation of the structural integrity of solid rocket propellant by means of the viscoelastic fracture mechanics approach at low and medium strain rates
(Elsevier, 2021) Martínez, Mario; López, Raúl; Rodríguez, Jesús; Salazar, Alicia
This work analyzes the influence of the displacement rate on the tensile properties and the fracture parameters, determined through a viscoelastic Fracture Mechanics approach, of carboxyl-terminated polybutadiene (CTPB) based solid composite propellants. Low and medium displacement rates attained in an electromechanical testing machine were inspected. From the true stress-true pseudo strain curves, the Young’s modulus was not influenced by the displacement rate with value almost identical to the instantaneous modulus obtained from stress relaxation tests. The same trend was achieved for the Poisson’s ratio, with a behavior close to incompressibility. On the other hand, the yield stress increased with the displacement rate rise. Regarding the fracture behavior, a strong dependency of the resistance curves in terms of both the viscoelasic J-integral and the viscoelastic crack tip opening displacement, CTOD, on the displacement rate was proved, being greater the fracture resistance as the displacement rate increases. Moreover, a linear relationship between the viscoelasic J-integral and the viscoelastic crack tip opening displacement was demonstrated. These results were confirmed by the fracture surfaces analysis. At low displacement rate, the damage nucleation and propagation occurred in the matrix while at high displacement rates, dewetting phenomena gave rise to rougher surfaces with damage initiation and growth mainly through the matrix – particle oxidizer interface.
Evaluation of the structural integrity of solid rocket propellant by means of the viscoelastic fracture mechanics approach at low and medium strain rates
(ELSEVIER, 2022-01-05) Martínez, Mario; López, Raúl; Rodríguez, Jesús; Salazar, Alicia
This work analyzes the influence of the displacement rate on the tensile properties and the fracture parameters, determined through a viscoelastic Fracture Mechanics approach, of carboxyl-terminated polybutadiene (CTPB) based solid composite propellants. Low and medium displacement rates attained in an electromechanical testing machine were inspected. From the true stress-true pseudo strain curves, the Young’s modulus was not influenced by the displacement rate with value almost identical to the instantaneous modulus obtained from stress relaxation tests. The same trend was achieved for the Poisson’s ratio, with a behavior close to incompressibility. On the other hand, the yield stress increased with the displacement rate rise. Regarding the fracture behavior, a strong dependency of the resistance curves in terms of both the viscoelasic J-integral and the viscoelastic crack tip opening displacement, CTOD, on the displacement rate was proved, being greater the fracture resistance as the displacement rate increases. Moreover, a linear relationship between the viscoelasic J-integral and the viscoelastic crack tip opening displacement was demonstrated. These results were confirmed by the fracture surfaces analysis. At low displacement rate, the damage nucleation and propagation occurred in the matrix while at high displacement rates, dewetting phenomena gave rise to rougher surfaces with damage initiation and growth mainly through the matrix – particle oxidizer interface.
Fatigue crack propagation behaviour of carboxyl-terminated polybutadiene solid rocket propellants
(Springer Link, 2020-02-10) López, Raúl; Salazar, Alicia; Rodríguez, Jesús
The fatigue crack growth behavior of composite solid carboxyl-terminated polybutadiene (CTPB) base propellants from a two stage-rocket has been analyzed. Both motors presented similar compositional percentage of the different constituents but while the booster motor presented aluminum as fuel and fine oxidizer particles, the sustainer motor presented nitroguanidine as fuel and coarse rigid inorganic particles. The fracture characterization revealed that the critical energy release rate values obtained from the grains of the booster motor were higher than those computed from the sustainer motor. The fatigue crack growth behavior of the propellant grains under study was comparable to that shown in rubber and the fatigue crack growth curves obtained from the booster motor were below those from the sustainer motor. The micromechanism of failure in both motors was microvoid nucleation and growth till the formation of a macro-crack capable of subcritical advancement. In the grains from the booster motor, the nucleation and progression of damage occurred through the matrix with fracture surfaces plain and with no trace of oxidizer particles. Instead, in the propellant grains from the sustainer motor, the damagewas generated in the particle–binder interface and the progression occurred along these interfaces leading to an abrupt fracture surface with discernible oxidizer particles. The mechanism of failure in the booster motor led to a better fatigue crack growth behavior and the irregular crack advancement in the sustainer motor implied a lower exponent of the crack growth rate to the energy release rate power law.
Influence of the notch sharpening technique on the fracture toughness of bulk ethylene¿propylene block copolymers
(Elsevier, 2010) Salazar, Alicia; Rodríguez, Jesús; Segovia, Angélica; Martínez, Antonio
Mechanical and fatigue behaviour of polyamide 12 processed via injection moulding and selective laser sintering. Analysis based on Kitagawa-Takahashi diagrams
(PERGAMON-ELSEVIER SCIENCE LTD, 2022-09-24) Salazar, Alicia; Cano, Alberto Jesús; Rodríguez, Jesús
This work deals with the mechanical and fatigue behaviour of polyamide 12 processed via Selective Laser Sintering and Injection Moulding. Apart from the analysis regarding the influence of the manufacturing technique, the effect of the layer orientation with respect to the direction of the applied load will be also analysed, since the additive manufacturing technique is a layer-wise technology that can induce anisotropy in the material. An extensive experimental program was carried out to determine the tensile, fracture, fatigue life and fatigue crack growth behaviours. The main novelty of this work lies, for the first time in polymers, in the use of the perspective of the Kitagawa-Takahashi diagrams for infinite fatigue life and by analogy their extension to failure.
Mechanical and fatigue behaviour of polyamide 12 processed via injection moulding and selective laser sintering. Analysis based on Kitagawa-Takahashi diagrams
(Elsevier, 2022) Salazar, Alicia; Cano, Alberto Jesús; Rodríguez, J.
This work deals with the mechanical and fatigue behaviour of polyamide 12 processed via Selective Laser Sintering and Injection Moulding. Apart from the analysis regarding the influence of the manufacturing technique, the effect of the layer orientation with respect to the direction of the applied load will be also analysed, since the additive manufacturing technique is a layer-wise technology that can induce anisotropy in the material. An extensive experimental program was carried out to determine the tensile, fracture, fatigue life and fatigue crack growth behaviours. The main novelty of this work lies, for the first time in polymers, in the use of the perspective of the Kitagawa-Takahashi diagrams for infinite fatigue life and by analogy their extension to failure.
Metallisation of additive manufactured polyamide 12 by low pressure cold spray
(Elsevier, 2024-03-15) Verdi, Davide; Merino-Millán, David; Salazar, Alicia
Cold Spray is a solid deposition process that can expand the field of application of polymeric materials thanks to the build-up of a metallic coating that improves their electrical properties and the wear resistance, among others. The novelty of the Cold Spray deposition on polymers has as drawback the lack of processing models that allow to choose the manufacturing parameters and forecast the coatings and substrates properties. In this work, the influence of the processing parameters for Aluminium-Zinc coating build-up via Low Pressure Cold Spray on polyamide 12 additively manufactured via Fused Filament Fabrication was investigated. Several sets of processing parameters combinations were systematically modified to establish the deposition window, leading to a final set that allowed to determine the physical, microstructural, and mechanical properties of the coatings, and the physical and thermal properties of the polymeric substrate. For the fixed gas pressure of 0.45 MPa and gas temperature of 500 °C, the scanning speed and the powder mass flow rate had a strong influence. Thick coatings (around 850 μm in size) were achieved at high powder mass flow rate (26 g/min) at the expense of low bond strength (between 1 and 3 MPa). The surface roughness acquired the highest values in those samples where erosion took place, occurring this phenomenon at small standoff distances and low powder mass flow rate, and no finding any relationship with the transverse gun speed. The generation of an interface layer of mixed metallic particles polymeric substrate plays a key role in the subsequent metallic coating growth, with thicknesses that ranged from 30 μm to 200 μm. In the substrate, the crystallinity degree of the polyamide underneath the coating increased, evidence of a heat affected zone where temperatures around the crystallisation temperature were reached, that also promoted stretching of the polymeric substrate due to dilatational phenomena. All this accompanied of an overall decrease in the thickness of the PA12 coupon after coating build up deposition with the high powder mass flow rate. This evidence indicates that a large plastic deformation of the polymeric substrate at the most energetic combination of processing parameters took place
On the failure assessment diagram methodology in polyamide 12
(PERGAMON-ELSEVIER SCIENCE LTD, 2022-05-21) Martínez, Mario; Cano, Alberto Jesús; Salazar, Alicia; Rodríguez, Jesús
For the first time, the Failure Assessment Diagrams of Polyamide 12, PA12, processed via a conventional technique as injection moulding, IM, and an additive manufacturing technique as Selective Laser Sintering, SLS, were determined via Finite Element Analysis (FEA) using a stress–strain equation more appropriate to describe the mechanical behaviour of thermoplastics. These diagrams were compared with those computed from the options of the BS 7910 standard applied for metals. The diagrams of SLS PA12 were clearly above that of IM PA12, presenting almost constant fracture ratio values for all the load ratios. This indicates the brittle behaviour, with small deviation from linearity, of SLS PA12 in comparison with IM PA12 which exhibited plasticity effects. This trend was supported by the mechanical response shown by PA12 manufactured by the different processing techniques. On the other hand, the diagrams obtained via FEA showed significant differences with the options of the BS 7910 standard, employed for the determination of the failure diagrams in metals, particularly when a Ramberg-Osgood model is used to describe the mechanical behaviour
Optimization of atmospheric low-power plasma spraying process parameters of Al2O3-50wt%Cr2O3 coatings
(ELSEVIER SCIENCE SA, 2018-09-18) Rico, Álvaro; Salazar, Alicia; Marlen Edith, Escobar; Rodríguez, Jesús; Poza, Pedro
The work is focused on the effect of the processing parameters of Al2O3-50wt%Cr2O3 coatings manufactured by low-power plasma spraying systems on the microstructure, mechanical properties, and tribological behaviour. Design of experiments followed by an optimization process using desirability functions has been applied for the selection of the processing parameters. The results indicate that power is the crucial parameter that controls the microstructure and consequently, the mechanical response of the coatings. At high powers, the highest volume of hard phases is attained, which leads to the highest hardness values and the best wear resistance at high applied loads. On the contrary, at low powers, the highest volume of spinels (tough phases) is observed, resulting in the highest indentation fracture toughness values and the best wear response at low applied loads. Therefore, the mechanical properties are directly related to the contents of the tough and hard phases.
Relevance of the femtolaser notch sharpening to the fracture of ethylene¿propylene block copolymers
(Elsevier, 2010) Salazar, Alicia; Rodríguez, Jesús; Segovia, Angélica; Martínez, Antonio
Structural Integrity of Aged Hydroxyl-Terminated Polybutadiene Solid Rocket Propellant
(Aerospace Research Central, 2017-07-04) López, Raúl; Órtega de la Rosa, Álvaro; Salazar, Alicia; Rodríguez, Jesús
The effect of aging time on the mechanical properties and fracture parameters determined via linear elastic fracture mechanics and elasto-plastic fracture mechanics approaches of an ammonium perchlorate hydroxyl-terminated polybutadiene solid propellant extracted from a stored in-service missile was evaluated. Accelerated thermal aging was carried out in air at 60°C for 3, 6, and 9 months, equivalent to natural aging at 23°C for 4, 8 and 12.5 years, respectively. For fracture tests, the in situ video imaging and the electrical resistance techniques were used for crack length measurements and the blunting line determination. The energy release rate and the J integral at crack growth initiation were identical for all the cases, evidence of an elastic nonlinear behavior. The source of the nonlinearity was caused by blunting, voiding, coalescing, and growing. The failure process zone extended 200 μm. The thermal oxidative aging process did not produce relevant changes in either the mechanical behavior or the fracture characterization, probably because the material under study was already naturally degraded. The influence was mainly observed in the slope of the blunting line determined experimentally for the long-term aged samples, which was between twice and three times higher than the unaged and short-term aged specimens. The microstructural evolution during the fracture test showed that the intergranular fracture caused by nonadherent particles was more evident with aging time.
The role of notching damage on the fracture parameters of ethylene-propylene block copolymers
(Elsevier, 2010) Salazar, Alicia; Segovia, Angélica; Martínez, Antonio; Rodríguez, Jesús
Understanding the failure of epoxy resin U-notched samples using cohesive models
(ELSEVIER, 2019-04-02) Serrano, Ana; Garrido, Miguel Ángel; Salazar, Alicia; Rodríguez, Jesús
The critical distances theory for predicting failure loads of notched solid polymers requires assuming very high values of the characteristic stress. These values have to be much higher than the nominal tensile strength without a reasonable explanation. The use of cohesive models for linear elastic materials also requires very high cohesive stress values so that the results of the models are closer to the experimental ones. This paper has analysed the failure of a batch of three-point bending specimens with different notch radii made of epoxy resin. Numerical simulations based on a cohesive model considering the elastic-plastic material have been carried out. The results are compared with previous results obtained from experimental three-point bending tests. Additionally, the effect of triaxiality on the cohesive stress values required to get good predictions of the experimental failure loads has been also analysed.