Wide Range Of Loading Rates Research Articles

Characterization of fracture behavior under impact-like loading conditions of elastomeric grades for high-pressure gas applications

Rapid gas decompression (RGD) is a major concern for elastomeric sealing components in cyclic gas exposure conditions as it generates cracks and can even cause total mechanical damage threatening the sealing integrity. Therefore, to analyze the fracture behavior of elastomeric grades under impact-like loading conditions, a test methodology was developed using a single edge notch in tension (SENT) specimen. To gain more insights into the behavior of differently formulated four nitrile butadiene rubber (NBR) grades (carbon black (CB) or Silica-filled, with different curing characteristics), tests were conducted at a wide range of temperatures, −20, 23, and 80 °C and under a wide range of loading rates (0.2–5 m/s). The single fracture parameters, strain energy release rate (G) at stable crack initiation and G at maximum load, as well as multiple fracture parameters from crack resistance curves (R-curves), G–Δa and crack growth rate vs crack extension curves, da/dt–Δa, were derived. All the grades showed distinct temperature and loading rate sensitivity on fracture behavior, however, the effect was more pronounced in sulfur-cured grades. Higher cross-link density, delivered a lower resistance to fracture and a uniform higher crack growth rate, conversely higher filler loading improved the fracture resistance. Within the tested conditions, the component-level instrumented tests on RGD failure revealed a similar ranking to the tested grades and it emphasizes the importance and relevance of intrinsic fracture properties. The generated information on single fracture parameters and crack growth kinetics is vital in phenomenological modeling attempts of the actual failure of components as well.

Dynamic mode II fracture mechanism of rocks using a novel double-edge notched flattened Brazilian disc specimen in the split Hopkinson pressure bar tests

The dynamic mode I fracture behaviors of rocks have been extensively investigated during recent decades, while the dynamic mode II fracture mechanism of rocks and its comparison with dynamic mode I fracture are poorly understood. In this study, a novel double-edge notched flattened Brazilian disc (DNFBD) specimen is introduced for dynamic mode II fracture toughness tests of rocks in the split Hopkinson pressure bar (SHPB) tests. First, using the finite element method (FEM), the stress distribution of the DNFBD specimen is analyzed and the stress intensity factors (SIFs) and the T-stress at the crack tips are determined. Then, dynamic mode II fracture tests are conducted on sandstone using the DNFBD specimen with proper specimen geometry configuration. High-speed photography and digital image correlation (DIC) results show that the shear crack initiates from the notch tips and propagates along the shear ligament of the DNFBD specimen, which demonstrates the reliability of the DNFBD-SHPB method for dynamic mode II fracture tests of rocks. Experimental results show that the dynamic mode II fracture toughness KIIC of rocks generally increases with increasing loading rate, exhibiting significant loading-rate dependence. For comparative investigation, dynamic mode I fracture tests using the notched semi-circular bend (NSCB) specimen are conducted on the same rocks. The results indicate that the mode II fracture toughness KIIC values are always higher than the mode I fracture toughness KIC values of rocks over a wide range of loading rates. The microscopic fracture mechanism of sandstone is interpreted based on the thin section observations. Under quasi-static loading, trans-granular (TG) fractures are more popular in the mode II fracture tests, while inter-granular (IG) fractures dominate the failure of mode I fracture. However, with the increase of loading rate, TG fracture becomes increasingly prevalent in both the dynamic mode II fracture and the dynamic mode I fracture of rocks. The results of this study are of great significance for understanding the dynamic mode II fracture mechanism of rocks.

Development of LaSAT and bonding strength evaluation of epoxy adhesive over a wide range of loading rates

ABSTRACT This study improved laser shock-wave adhesion test (LaSAT) to evaluate the bonding strength of an aluminum alloy/epoxy resin adhesive, since the bonding strength is dependent on loading rate. In this method, strong shock wave due to laser ablation induces interfacial fracture, and the critical stress is computed using numerical simulations of the FEM. To accurately evaluate the bonding strength, the input waveform caused by laser ablation was identified for FEM computation. Such ablation impact (pressure vs. time) and its spatial distribution of ablation impact were experimentally investigated, and this study computed stress-wave propagation in the specimen. It is found that numerical simulation with FEM reproduced well the wave propagation. A wide range of loading rates was achieved by the quasi-static tensile test, split Hopkinson pressure bar (SHPB) test, and LaSAT. As a result, bonding strength exhibited a significant dependence on the strain rate, similar to that of bulk resin materials in general.

Autowave nature of the Lüders deformation in a substitutional FCC alloy

Lüders deformation in an aluminum-magnesium alloy was studied in a wide range of loading rates. It was found that the deformation is always accompanied by the propagation of deformation fronts, which move either continuously or intermittently depending on the strain rate. The kinetics of fronts is determined by the reaction of active deformable media to an external mechanical action and is determined by the autowave nature of plastic deformation.

Tensile properties of 2D-C/SiC composites at temperatures up to 1873 K at wide-ranging strain rates

We determined the tensile properties of 2D-C/SiC composites at temperatures up to 1873 K with a wide range of loading rates (10−3 s−1 and 400 s−1) in argon and air. We developed a high-temperature Hopkinson tensile bar with tensile strength based on the loading rate, temperature, and oxidation. Under high loading rates, tensile strength was influenced by the nucleation of multiple cracks and the improvement of C-fiber pull-out length and interface strength. In argon, material component performance and thermal residual stress influenced the 2D-C/SiC high-temperature tensile properties. In air, oxidation damage significantly affected the tensile properties of 2D-C/SiC regardless of loading rate or temperature. This led to lower tensile strength and higher strain rate sensitivity. Our observations can enhance the understanding of the failure mechanism of thermo-chemo-mechanical coupling in 2D-C/SiCs and will provide guidance for safe application in extremely high-temperature conditions.

Теория нагружения синтетических рыболовных материалов

An important task of mechanics of synthetic fishing twisted rope and string products and braided cords is to create a fundamental basis for describing their fracture processes during deformation in operation, i.e. to develop a framework for fracture mechanics (building models and algorithms for calculating structures and technological processes at large plastic deformations, taking into account fracture). There is considered the necessity of developing and introducing the simple and at the same time effective criteria of destruction, allowing to estimate reliably the conditions of safe operation of twisted rope and string products, threaded products and braided cords and especially the structures of industrial fishing gear. Determination of stress concentrations, is an obvious task in connection with the creation of new fishing trawls, purse seines and grips with complex shape-changing geometry. This problem is actual for many branches of industry, including transport and machine-building, where at the designing stage it is necessary to take into account possible emergency situations caused by intensive dynamic effects in twisted rope and string, threaded products and braided cords. Components and structures of twisted rope and string products, threaded products and braided cords should withstand the specified loads in a wide range of loading rates. In particular, the theory allows to solve nonlinear problems, taking into account changes in geometry of deformable twisted rope and string products, threaded products and braided cords, as well as to obtain analytical solutions of various problems.

Mesh objectivity in dynamic fracture analyses with rate dependent continuum damage models

This paper is aimed at investigating the mesh objectivity in dynamic fracture analyses employing strain rate dependent damage evolution as the localization limiter. Specifically, the goal is investigating and understanding the limits of applicability across various loading rates. For this purpose, dynamic fracture of a brittle material is simulated using a rate dependent scalar damage model. Dynamic fracture scenarios under a wide range of loading rates are considered, which yield various fracturing patterns ranging from localized to branched/diffused. The rate dependent damage model is seen to yield mesh objective predictions only at higher loading rates, which correspond to branched/diffused fractures. Results are not mesh objective at lower loading rates, which correspond to localized fractures. The regularization effect, at higher rates, is due to an intrinsic length-scale induced by the rate dependent damage law, and is related to the strain rate sensitivity parameter. For these cases, the predicted fracture patterns consist of thickened damage bands, spanning multiple element widths, and are wider than the intrinsic length-scale induced by the model. Thus, this feature can be viewed as a physical manifestation of the intrinsic length-scale. Wave propagation and dispersion in a one-dimensional version of the present damage model is analyzed further to explain the results. It is demonstrated that the group and phase velocity are finite and approach the elastic wave speed at higher loading rates, helping retain mesh objectivity. However they approach infinity at lower loading rates, causing the regularizing effect to vanish. Thus, the rate dependent damage model does not yield mesh objective results across all loading rates, and must be employed with caution.

Rate‐dependent mechanical response of polypropylene nonwovens

AbstractMost nonwoven products are subjected to a variety of loading rates ranging from low‐speed quasi‐static loads to high‐speed dynamic loads during their life cycles. Understanding their response to a wide range of loading rates is critical to proper usage and effects how rapidly one can process them. In this work quasi‐static to high strain rate experiments (10−3 to 100 to 400 strain/s) are investigated. The results from analyzing the rate‐dependent properties show an increase in the strength and modulus accompanied by a reduced strain to failure in nonwovens as the strain rate increases. Higher basis weight samples showed more prominent rate‐dependent properties across all loading rates and fiber orientations. Ductile to brittle transition in the material failure mechanisms were observed. The specimens with rectangular and circular bonding patterns show higher strain localization than the specimens with the diamond bonding pattern due to the higher fiber reorientation. The rate dependent response at higher loading rates does not follow the typical rate dependent models of Johnson–Cook and Cowper–Symonds. This is a vital understanding as the material greatly stiffens up at higher rates and has a much lower strain to failure than one would expect.

Finite element modeling of dynamic fracture in concrete through the initial fracture toughness-based criterion and field variable transference technique

Objective of the present study is to model the mode I dynamic crack propagation of concrete three-point bending (TPB) beams by using an initial fracture toughness-based criterion, and to evaluate the contribution of the rate and the inertia effects to the dynamic responses of concrete beams during crack growth. Firstly, the theory and implementation of the initial fracture toughness-based criterion are described in detail. Specifically, a field variable transference (FVT) technique is introduced to realistically reflect the coupling effect of the moving cracks and stress waves. Then, analysis procedures for static and dynamic crack growth are established. The comparison between the simulated and experimental impact and reaction forces indicates that, the initial fracture toughness-based criterion can accurately predict the mode I dynamic crack extension in concrete TPB beams. Moreover, the effects of the inertia and rate effects on dynamic responses (i.e., load, deformation, crack propagation velocity, and energy evolution and partition) are evaluated by performing numerical experiments on the mode I crack growth of TPB beams under a wide range of loading rates from 0.0002 mm/s to 2000 mm/s. It is concluded that, for the adopted concrete TPB beams, the inertia effect can be neglected and only the rate effect needs to be taken into account if the loading rate does not exceed 2 mm/s. Otherwise, if the loading rate exceeds 500 mm/s, only the inertia effect needs to be considered. In addition, the effect of damping on dynamic responses is investigated, and it is found that the damping effect can be ignored at high loading rates.

Dynamic shear fracture behavior of rocks: insights from three-dimensional digital image correlation technique

The influence of the loading rate on the mode I fracture property of rocks has been extensively investigated through experiments. However, the rate-effect of the dynamic mode II fracture has rarely been reported. This study employed the modified split Hopkinson pressure bar (SHPB) system to conduct a series of dynamic mode II fracture tests under a wide range of loading rates using the modified short-core-in-compression (SCC) method. The complete dynamic fracture processes of rock were observed using the three-dimensional high-speed digital image correlation (3D HS DIC) technique. The results reveal that the dynamic mode II fracture toughness increases with the loading rate at a power relationship. By virtue of the evolution of the surface principal strain and displacement, the dynamic fracture and damage process and the deformation characteristic of the SCC specimen were analyzed in detail. The dynamic fracture processes are divided into the elastic stage, plastic deformation stage, unstable crack growth stage, and post fracture stage. The crack propagation path of the SCC specimen was obtained under impact loading. It was found that new cracks first initiate from two notch tips and then propagate toward the central area in the expected shear fracture band (ESFB); the path is nearly independent of the loading rate. Additionally, the macro–micro fracture surface morphology of the SCC specimen was measured using a 3D optical scanner as well as scanning electron microscope (SEM) respectively. It was found that the roughness and curvature in the fracture surface created by shearing generally decrease as the loading rate increases, in accordance with fractal theory. The SEM result indicates intergranular fracture occurs more frequently on the shear fracture surface under static loading, while transgranular fracture is more common on the shear fracture surface at high loading rates.

Formulation and Numerical Solution of the Stability Loss Problem of Elastic-Plastic Shells of Revolution with an Elastic Filler under Combined Axisymmetric and Torsional Loadings

A dynamic statement and a method for numerically solving the buckling problems of elastoplastic shells of revolution with filler in axisymmetric and non-axisymmetric shapes under quasi-static and dynamic loading are presented within the framework of two approaches. In the first approach, the problem of elastic-plastic deformation and buckling of shells of revolution with an elastic filler under combined axisymmetric loading with torsion is formulated in a two-dimensional (generalized axisymmetric) formulation based on the hypotheses of the shells theory of the Timoshenko type and the Winkler foundation. The constitutive relations are written in the cylindrical system of Euler coordinates. For each shell element, a local Lagrangian coordinate system is introduced. Kinematic relations are recorded in the current state metric. The distribution of the displacement velocity components over the shell thickness and strain rate tensors in the local basis is written as the sum of the momentless and moment components, which, in turn, are written as the sum of the symmetric and asymmetric parts in the local and in the general basis. The elastoplastic properties of the shell material are taken into account within the framework of the theory of flow with nonlinear isotropic hardening. To take into account non-axisymmetric forms of buckling, the desired functions (both displacements and forces, moments, contact pressure) are expanded into a Fourier series in the circumferential direction. The variational equations of shell motion are derived from the general equation of dynamics. The contact between the shell and the deformable filler is modeled based on the conditions of non-penetration along the normal and free slip along the tangent. The variational equations of shell dynamics for axisymmetric and nonaxisymmetric processes are interconnected through the physical relations of the theory of plasticity. They take into account large axisymmetric shape changes and the instantaneous stress-strain state of the shell. At the initial stage of the nonaxisymmetric buckling process, the deflections are small; therefore, the equations of nonaxisymmetric buckling are obtained as linearized with respect to nonaxisymmetric forms. To initiate nonaxisymmetric buckling modes, initial nonaxisymmetric deflections are introduced. To solve the defining system of equations, a finite-difference method and an explicit time integration scheme of the “cross” type are used. The second approach is based on continuum mechanics hypotheses and implemented in a three-dimensional setting. Both approaches make it possible to simulate the nonlinear subcritical deformation of shells of revolution with an elastic filler, to determine the ultimate (critical) loads in a wide range of loading rates, taking into account geometric shape imperfections, to study the processes of buckling in axisymmetric and non-axisymmetric shapes under dynamic and quasi-static complex loading by tension, compression, torsion, internal and external pressure. The results of numerical simulation are compared with experimental data on the torsion of steel cylindrical elastoplastic shells ( R / h = 1.45) with an elastic filler.

Fracture characteristics of sustainable crumb rubber concrete under a wide range of loading rates

The dynamic mechanical properties of concrete materials significantly influences the safety of construction under impact loads. In this study, a comprehensive experiment on the crack straight-through flattened Brazilian disc specimens of crumb rubber concrete (CRC) is undertaken. Three specific experiments were performed to obtain the wide loading-rate ranges of fracture characteristics, i.e., the quasi-static test, drop-hammer impact test, and split Hopkinson pressure bar test. The measured and calculated results are also discussed. The results reveal that the fracture toughness and energy are both positively correlated with loading rate. Moreover, a transition loading rate (around 1 GPa × m1/2/s) exists between the high and low loading rates, and the enhancing effect of high loading rate on fracture toughness cannot be neglected. The analysis of the dynamic increased factor (DIF) on the fracture toughness (DIFk) and fracture energy (DIFg) of CRC shows that DIFk and DIFg are related to the rubber content. Furthermore, the analysis demonstrates that crumb rubber particles can enhance the crack resistance of concrete under dynamic loads. Accordingly, empirical models for the DIFk and DIFg of CRC are proposed based on the experimental data. In addition, the mechanisms by which the loading-rate affects the fracture characteristics were preliminarily identified by observing the failure modes under various loading-rate loads. This study is intended to help spread the application of crumb rubber in concrete materials.

Investigation on brittle-ductile transition of PMMA mode-II fracture using time-temperature superposition principle

The rate-temperature dependent brittle-ductile transition (BDT) behavior of PMMA (polymethyl methacrylate) mode-II fracture was investigated through tensile-loading shear fracture (TLSF) tests. The dimensionless ratio KJC/KIIC was chosen as the index to identify the brittle/ductile state. Assuming the fracture property to be viscosity-dominated, the time-temperature superposition principle based on the Arrhenius equation was adopted. The master curves of KJC/KIIC in a wide range of loading rate and temperature were constructed with the experimental data obtained under limited test conditions. With the derived critical BDT band from the master curve, the BDT state of PMMA’s fracture under complex loading conditions was successfully predicted and experimentally validated. The results are helpful to describe the BDT behavior and provide an equivalent approach to investigate the mode-II fracture which can substantially save the experimental cost and time.

Theoretical predictions of dynamic necking formability of ductile metallic sheets with evolving plastic anisotropy and tension-compression asymmetry

In this paper, we have investigated necking formability of anisotropic and tension-compression asymmetric metallic sheets subjected to in-plane loading paths ranging from plane strain tension to near equibiaxial tension. For that purpose, we have used three different approaches: a linear stability analysis, a nonlinear two-zone model and unit-cell finite element calculations. We have considered three materials –AZ31-Mg alloy, high purity α-titanium and OFHC copper– whose mechanical behavior is described with an elastic-plastic constitutive model with yielding defined by the CPB06 criterion (15) which includes specific features to account for the evolution of plastic orthotropy and strength differential effect with accumulated plastic deformation (48). From a methodological standpoint, the main novelty of this paper with respect to the recent work of N’souglo et al. (42) –which investigated materials with yielding described by the orthotropic criterion of Hill (24)– is the extension of both stability analysis and nonlinear two-zone model to consider anisotropic and tension-compression asymmetric materials with distortional hardening. The results obtained with the stability analysis and the nonlinear two-zone model show reasonable qualitative and quantitative agreement with forming limit diagrams calculated with the finite element simulations, for the three materials considered, and for a wide range of loading rates varying from quasi-static loading up to 40000 s− 1, which makes apparent the capacity of the theoretical models to capture the mechanisms which control necking formability of metallic materials with complex plastic behavior. Special mention deserves the nonlinear two-zone model, as it does not need prior calibration –unlike the stability analysis– and it yields accurate predictions that rarely deviate more than 10% from the results obtained with the unit-cell calculations.

A cyclic visco-plastic constitutive model for the ratcheting behavior of U75VG rail steel under a wide range of loading rates

The uniaxial tension, strain-controlled and stress-controlled cyclic deformation experiments of U75VG rail steel at various loading rates were carried out. Experimental results show that the U75VG rail steel shows obvious rate-dependent tension, cyclic softening feature and ratcheting behavior. Moreover, based on the rate-dependent experimental results, a new cyclic visco-plastic constitutive model was established by introducing the rate-dependent isotopic resistance and ratcheting factor into isotropic and kinematic hardening rules, respectively. Compared with the classic cyclic visco-plastic model, the proposed model can reasonably simulate the tension, strain-controlled and stress-controlled cyclic deformation behaviors at different loading rates. Finally, the prediction capacity of ratcheting behavior under a wide range of loading rates was demonstrated.

Modified cohesive zone model for soft adhesive layer considering rate dependence of intrinsic fracture energy

The cohesive zone model (CZM) has been extensively utilized to investigate the cohesive failure of the soft adhesive layer. This paper has proposed a modified CZM considering the rate dependence of the intrinsic fracture energy as well as the dissipative energy. The evolution of the intrinsic fracture energy with loading rate was established based on Chaudhury’s model, and the dissipative energy was described by the Maxwell model. After implemented into FEM, the proposed CZM was validated by the double cantilever beam (DCB) debonding test data and the effect of the rate-dependent intrinsic fracture energy on the cohesive failure of soft adhesive layer was further investigate. The limitation on the wide loading rate range was solved by introducing the rate-dependent intrinsic fracture energy. The phenomenon that the dissipative energy is affected by the evolution of the intrinsic fracture energy can be described. The experimental observable fibrillation zone of the soft adhesive layer can be taken as the criterion for whether considering the rate dependence of intrinsic fracture energy or not. The modified CZM is a promising approach for describing the cohesive failure of the soft adhesive layer.

Quasi-static and dynamic fracture toughness of a γ-TiAl alloy: Measurement techniques, fractography and interpretation

Intermetallic titanium aluminides (TiAl) offer an enormous potential for high temperature applications due to their high specific strength, creep and oxidation resistance. However, their use for structural components is limited by their low ductility and fracture toughness. During service, along with a high number of load cycles, the material may also be subjected to unexpected impact loads, which requires therefore knowledge about dynamic material parameters for a damage-tolerant component design. Here we present a feasibility study to determine the fracture toughness of a third generation TiAl-alloy over a wide range of loading rates. Quasi-static crack resistance curves (R-curves) were determined using the direct current potential drop (DCPD) technique. The dynamic experiments were performed with a drop tower with impact velocities ranging from 1 to 10 m/s on pre-cracked SENB specimens. To exclude the influence of inertial forces, the measurements were carried out with strain gauges applied in the elastic near-field of the crack tip. Despite a critical consideration of possible systematic errors of this measurement method, it was found that the dynamic fracture initiation toughness slightly increases up to loading rates of K̇I = 106 MPa√m/s. The fracture behaviour of the material and possible reasons for the toughness increase are discussed based on comprehensive fractographic investigations as well as crack path analyses within the microstructure.

Modelling of temperature and strain rate dependent behaviour of pearlitic steel in block braked railway wheels

Block braked railway wheels are subjected to thermal and rolling contact loading. The thermal loading results in high temperatures and thermal stresses which cause slow time dependent processes such as creep, relaxation and static recovery of the wheel material. At the same time, the rolling contact loading implies a very fast mechanical load application. This paper is focused on material modeling of pearlitic steel for a wide range of loading rates at elevated temperatures. The starting point is a viscoplasticity model including nonlinear isotropic and kinematic hardening. The Delobelle overstress function is employed to capture strain rate dependent response of the material. The model also includes static recovery of the hardening to capture slower viscous (diffusion dominated) behaviour of the material. Experiments for the pearlitic wheel steel ER7 in terms of cyclic strain-controlled uniaxial tests with hold-time, uniaxial ratchetting tests including rapid cycles and biaxial cyclic tests with tension/compression and torsion are used to calibrate the material model. These experiments were performed under isothermal conditions at different temperatures. In the ratchetting tests, higher loading rates are obtained and these have been used to calibrate the high strain rate response of the viscoplasticity model. The paper is concluded with a numerical example of a block braked wheel where the importance of accounting for the viscoplasticity in modelling is highlighted.

Locating the optimal microstructural state against dynamic perforation by evaluating the strain-rate dependences of strength and hardness

Intense research efforts have been made to understand the variation of strength with strain rate, while the mechanisms governing the strain-rate dependence of hardness have been rarely studied. In this work, we conducted a comprehensive investigation on strength, hardness and failure mechanism of AISI 4340 steels with 4 different microstructural states in a wide range of loading rate. We found strain-rate hardening behavior in all 4 steels, while the degree of hardening, characterized by the normalized dynamic strength (NDS) or the normalized dynamic hardness (NDH), depends on not only materials but also loading modes. With the increase of material strength, the NDS significantly increases but the NDH decreases slightly. The inconsistency between the variations of NDS and NDH is because the hardness is governed by not only yield strength but strain-hardening ability. Although the yield strength increases as rising strain rate, the strain-hardening ability reduces obviously, particularly for high-strength materials due to shear softening under dynamic loading conditions, which also causes a transition from homogeneous deformation to shear fracture. The variations of NDS and NDH could reflect the trends for resisting not only the ductile perforation (strength limited) but also the shear plugging failure (toughness limited), allowing to propose a criterion for locating the optimal strength-toughness combination against dynamic perforation, which was further verified by the ballistic penetration testing results. Moreover, similar behaviors of NDS and NDH of various other alloys were also found, which may suggest the extensive applicability of the current approach.

Characterization of the Fatigue Behavior of SLS Thermoplastics

The selective laser sintering (SLS) is an additive manufacturing technology with clear potential for producing high quality polymeric components of various thermoplastic polymers and elastomers which can be used in demanding engineering applications under complex service loading conditions. The prerequisite for these applications is that the stiffness and the tensile strength of the SLS specimens is in the same range as for injection molded specimens using a proper parameter set of the SLS process and qualified materials. While the tensile strength of SLS printed polymers is recently determined by many researchers, hardly any data are available about the fatigue behavior of SLS polymers on specimen level and even less on component level. Cylindrical specimens with and without round notch have been designed and additively manufactured using PA12 and TPU SLS grades in two different printing directions (vertical and horizontal). The monotonic tensile behavior was characterized over a wide loading rate range (0.1 to 100 mm/s) and the tensile strength and failure strain values were determined. The fatigue behavior was characterized under cyclic loading conditions at various stress ratios (R=0.1, -1), at a constant frequency of 5 Hz at 5 stress levels. Stress vs. cycle number-to-failure, Nf points were determined for constructing conventional S-N curves for the materials investigated. A distinct anisotropy of the tensile strength and failure strain was recognized for the SLS TPU investigated.