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Basalt fabric composite, with different twill wave reinforcements, i.e. twill 2/2 and twill 1/3, have been studied in this work by means of experimental tests and numerical finite element (FE) simulations. As fabric reinforcements show repeating undulations of warp and fill yarn, simple mixtures law cannot be applied.
As a consequence, the mesoscopic scale, lying between the microscopic and the macroscopic one, has to be taken into account to mechanically characterize a fabric reinforced composite. The aim of this work is to evaluate the stiffness of a fabric reinforced composite in warp and fill direction. In particular a numerical FE
model, assuming elliptical sections and sinusoidal shape of the yarns, has been implemented and experimental tests have been carried out in order to validate the proposed model. Finally, the strength and the failure modes le orientation, have been experimentally investigated.
Purpose:
A prepreg production device in laboratory scale is used to develop the production process of unidirectionally reinforced prepregs.
Design/methodology/approach:
The aim of the prepreg production device is to impregnate different types of reinforcement fibers with an arbitrarily selectable thermoset matrix system that completely satisfies the requirements for autoclave processing. As the prepreg production device is designed and built up modularly every module corresponds one step in the process.
Findings:
To identify the parameters of the production process and investigate its sensitivity on the material quality of both the prepreg as an uncured semi-finished product and the composite as the cured material experimental investigations regarding the resin flow, fiber volume content, mass per unit area and void content are carried out. Overall four material combinations have been investigated, where in each case the selected impregnation temperature and the width of the impregnation gap has been reproducibly varied in selected steps.
Research limitations/implications:
The experimental characterization of the prepregs and of the composite material is carried out according to German standards.
A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by analytical and numerical investigations. Due to the definition of plain representative sequences of balanced plain-weave fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. The mesomechanic kinematic can be observed in both the analytic model and the FE-analyses. The analytic model yields hyperbolic correlations due to the strongly simplifying presumptions that neglect elasticity. In contrast the FE-analyses yield linear correlations in much smaller amounts due to the consideration of elastic parts, yet distinctly.
Musculoskeletal simulations of lumbar spine loading rely on a geometrical representation of the anatomy. However, this data has an inherent inaccuracy. This study evaluates the influence of defined geometrical parameters on lumbar spine loading utilising five parametrised musculoskeletal lumbar spine models for four different postures. The influence of the dimensions of vertebral body, disc, posterior parts of the vertebrae as well as the curvature of the lumbar spine was studied. Additionally, simulations with combinations of selected parameters were conducted. Changes in L4/L5 resultant joint force were used as outcome variable. Variations of the vertebral body height, disc height, transverse process width and the curvature of the lumbar spine were the most influential.
These parameters can be easily acquired from X-rays and should be used to morph a musculoskeletal lumbar spine model for subject-specific approaches with respect to bone geometry. Furthermore, the model was very sensitive to uncommon configurations and therefore, it is advised that stiffness properties of discs and ligaments should be individualised.
Purpose:
The present work deals with the experimental investigation concerning the energy dissipation capacity of different kinds of reinforcement fibres in monolithic and hybrid layups under high velocity impact loads. The investigated kinds of fibres are carbon, glass and basalt. Design/methodology/approach:
The test panels have been impregnated with thermoset resin. Curing was done by autoclave processing. In order to obtain comparable fibre volume contents of approx. 60 % in the different layups (monolithic and hybrid without and with separating layer), curing cycles adapted to the type of layup have been identified. The resulting fibre volume content of the test panels has been determined both by weighing and experimentally by chemical extraction and calcination. The impact load was applied by an instrumented experimental setup. Thereby both commercially available bullets and bearing balls accelerated with weighted propellant in a sabot have been used as impactors. The measured values are the velocities of the bearing balls as the impactor before and after penetration of the test panels.
Findings:
In both cases the results show the energy dissipation capacity of each single kind of fibre in case of the monolithic layups as well as the enhanced properties of the hybrid stacked layups without and with the separating layer as a core material. Typical failure modes on the impact surface and on the outlet areas are identified.
Research limitations/implications:
The influence of the respective kind of impactors, namely bullets and bearing balls, on the evaluated results is identified. Thereby the bearing balls exhibited a higher degree of reproducibility due to several reasons.
Originality/value:
Fibre reinforced plastics with hybrid stacking sequences can be used as load-bearing structures and at the same time as safety structures for passengers in automotive or aerospace applications. Moreover, with the hybrid stacked composites lightweight concepts can efficiently be realized regarding energy saving issues.
Purpose:
A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by numerical investigations.
Design/methodology/approach:
Due to the definition of plain representative sequences of balanced plain-weave and twill-weave 2/2 fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation.
Findings:
The mesomechanic kinematic can be observed in the FE analyses for both kinds of fabric constructions.
Research limitations/implications:
The FE analyses consider elasticity and contraction due to Poisson effects, respectively, of the model under selected longitudinal strains. Practical implications: The results are evaluated at relevant positions on the centre-line of the ondulated warp-yarn of the plain representative model. A direct and linear coupling in case of the transversal kinematic behaviour, and thereby a corresponding definite reduction of the evaluated longitudinal strains in terms of the difference of the applied and determined longitudinal strains is identified.
Originality/value:
Both characteristic purely kinematic reactions due to geometric constraints directly depend on the introduced degree of ondulation. This non-dimensional parameter relates amplitude and length of one complete ondulation, and thus represents the intensity of the ondulation of the respective fabric construction.
This paper describes the results of tensile tests and finite element (FE) calculations with representative volume elements (RVEs) of basalt fibre reinforced plastic with two different types of fabric reinforcements. As fabric reinforcements show repeating ondulations of warp and fill yarn, simple mixtures laws reach their limits. That is the reason why the mesoscopic dimension, lying between the microscopic and the macroscopic dimension, has to be taken into account when a mechanical characterization of fabric reinforced composites is carried out. The aim of this work is to determine the stiffness of a fabric reinforced composite in warp and fill direction with numerical investigations. The simulations are based on FE-calculation with two different RVEs. The tensile tests and the FE-calculations have been carried out for two different types of basalt fabrics, namely twill 2/2 and twill 1/3. The comparison between the experimental data and the results of the FE-calculations are provided in order to support the validity of the proposed model.
Structural mechanic properties of fiber reinforced plastics depend on the single components’ properties, namely matrix and fiber [5]. Simple micromechanic homogenization theories reach a limit when a laminate consists of fabric reinforced layers instead of unidirectional layers. The ondulations of warp and fill yarn caused by the textile semi-finished product are the reason why the mesoscopic scale, which is in between the microscopic and the macroscopic scale, has to be taken into account when mechanically characterizing fabric reinforced composites [3]. In this scale a mesomechanic kinematic can be derived analytically. Especially, when considering free damped vibrations of structures the repeated acting of the kinematic correlation significantly affects the damping behaviour to higher values compared to theoretically predicted damping ratios. The model is investigated using Finite-Element-Analyses and basically validated experimentally.