Compression-compression Loading Research Articles

Fiber fracture behavior of high-pressure resin transfer molded (HP-RTM) carbon/epoxy multidirectional laminates under compression-compression fatigue loading

The influence of different stress levels on the fatigue life and fracture behavior of laminated composites have been evaluated under compression-compression (C–C) loading conditions. Carbon/epoxy multidirectional (MD) laminate specimen was designed with eight layers [0°, ± 45°, 0°]s of unidirectional plies. The preforms were molded by a high-pressure resin transfer molding (HP-RTM) process. As part of the study, a static compression test was performed. The C–C fatigue loads were applied at −260 MPa, −280 MPa, −300 MPa, and −320 MP compression stress until failure or two million cycle loadings. The fatigue limit has been obtained at −265 MPa stress by stress-cycle number (S-N) curve analysis, which is 51.4 % of static compression strength. The damage behavior was identified after C–C fatigue tests. By using optical and scanning electron microscopy, fiber fracture, matrix cracking, and fiber/matrix interface debonding were observed. Under the C–C fatigue loading conditions, fiber fracture modes were characterized by rough cross-sections, shear, and line-shaped edges.

Accelerated fatigue life diagram characterization of CFRP

There are several ways to obtain the fatigue life behavior of composite materials, such as the application of classical theories or complex progressive damage models. Recently, constant life diagrams have demonstrated good effectiveness in predicting the fatigue life of CFRPs. Nevertheless, the large number of tests required, and the time necessary for the characterization, makes this method very expensive in terms of time and resources. The aim of this work is the evaluation of accelerated characterization techniques in addiction with statistical methods, to obtain constant fatigue life diagrams of CFRPs, with a reduced number of tests and a shorter characterization time. The results show that, combining universal and accelerated testing techniques with statistical methods, it is possible to obtain constant life diagram for the whole range of tension-tension, tension-compression, and compression-compression loading modes, with a reduced number of tests. Moreover, it is observed that, the accelerated characterization techniques show a fatigue life limit similar to the conventional ones.

Anti-buckling device for biaxial testing with cruciform specimens

The use of an anti-buckling device is proposed to avoid the appearance of undesired instabilities during biaxial testing with cruciform specimens in which the compressive loads are applied directly on the arms of the sample by means of compression plates. The device consists on a cross-shaped accessory that restricts out-of-plane displacements and a L-shaped support that forces the alignment of the fixture, the specimen and the testing machine. In addition, recommendations about the test methodology and the conditioning of the cruciform sample are given. For this purpose, analytical and numerical studies are developed to design the experiments and to describe both the global buckling of the cruciform specimen and the local instability of the central region subjected to biaxial loading. The risk of instability in the arms of the sample is reduced under tension-compression and compression-compression loading cases whenever the device is used, ensuring that the results are not affected by premature buckling of the specimen and favoring the appearance of appropriate failure modes.

Long-term mechanical properties of a novel low-modulus bone cement for the treatment of osteoporotic vertebral compression fractures

In spite of the success of vertebroplasty (VP) and balloon kyphoplasty (BKP), which are widely used for stabilizing painful vertebral compression fractures, concerns have been raised about use of poly(methyl methacrylate) (PMMA) bone cements for these procedures since the high compressive modulus of elasticity (E) of the cement is thought to be one of the causes of the higher number of adjacent-level vertebral fractures. Therefore, bone cements with E comparable to that of cancellous bone have been proposed. While the quasi-static compressive properties of these so-called “low-modulus” cements have been widely studied, their fatigue performance remains underassessed. The purpose of the present study was to critically compare a commercial bone cement (control cement) and its low-modulus counterpart on the basis of quasi-static compressive strength (CS), E, fatigue limit under compression-compression loading, and release of methyl methacrylate (MMA). At 24 h, mean CS and E of the low-modulus material were 72% and 77% lower than those of the control cement, whereas, at 4 weeks, mean CS and E were 60% and 54% lower, respectively. The fatigue limit of the control cement was estimated to be 43–45 MPa compared to 3–5 MPa for the low-modulus cement. The low-modulus cement showed an initial burst release of MMA after 24 h followed by a plateau, similar to many other commercially available cements, whereas the control cement showed a much lower, stable release from day 1 and up to 1 week. The low-modulus cement may be a promising alternative to currently available PMMA bone cements, with the potential for reducing the incidence of adjacent fractures following VP/BKP.

A Novel Thermgoraphic Methodology to Predict Damage Evolution of Impacted CFRP Laminates Under Compression-Compression Fatigue Based on Inverted Weibull Model

A novel thermographic methodology is proposed in this work to predict damage evolution of impacted CFRP laminates under compression-compression fatigue loading based on inverted weibull model. To this goal, the inverted weibull model is firstly mathematically proposed. Then, several specimens are subjected to impact testing, followed by fatigue testing and monitored by infrared thermography. Afterwards, the thermal image and the surface temperature of specimens are analyzed. Finally, taking the surface temperature as damage variables, the inverted weibull model is introduced to predict the damage evolution. The obtained results show that the inverted weibull model can be used for damage evolution prediction with the predicted error less than 10%.

Fatigue Behaviour of Triaxial Braided Composites under Tension-Tension and Compression-Compression Loading

The fatigue behaviour of [0°/±45°] triaxial braided composites is investigated. Tension-tension and compression-compression loading is chosen to study main damage mechanisms and their effect on the stiffness degradation. In both cyclic loading cases a high stiffness degradation can be observed shortly after the start of cyclic loading. Inter-fibre fractures in the braid yarns with subsequent delaminations are responsible for this behaviour during tension-tension loading. Compression-compression loading leads to kink band formation in the axial yarns favoured by yarn undulations. In consequence of the observed material degradation, S-N curves based on a defined level of stiffness degradation are proposed for fatigue dimensioning instead of load cycles to fracture.

Influence of Reversed Fatigue Loading on DamageEvolution of Cross-Ply Carbon Fibre Composites.

Microcrack formation and delamination growth are the main damage mechanisms in the fatigue of composites. They lead to significant stiffness loss, introduce stress concentrations and can be the origin of subsequent damage events like buckling or fibre breakage, especially in case of shear and compression stresses during load reversal. Fatigue experiments of carbon fibre reinforced laminates were conducted at several stress ratios and analysed in terms of crack and delamination growth. These investigations were accompanied by microscopic imaging, digital image correlation and finite element modelling to take into account the effects of residual stresses and crack closure. It was found that residual stresses significantly change the local stress ratio in off-axis layers and lead to residual crack opening of inter fibre cracks. These cracks remain open and close under high compression loadings only. Furthermore, crack formation under pulsating compression loading turned out to be driven by residual stresses leading to perpendicular cracks as observed under pure tension loading. The experimental findings further confirm the severe detrimental effect of tension-compression loading on crack formation and delamination growth compared to pulsating tension-tension or compression-compression loads.

Two simplified methods for fatigue crack growth prediction under compression-compression cyclic loading

Submersibles and submarines are subject to cyclic compressive sea loading during their service life, which is quite different from the ships and platforms under tensile and bending loading. It is important to study the fatigue crack propagation under cyclic compression in order to assess the fatigue life of the submersible and submarine. An extended McEvily model is proposed for the fatigue crack growth prediction under cyclic compression-compression loading. First, Finite Element Method (FEM) simulation and a simplified stress estimation method are proposed for efficient fatigue crack growth analysis. In the Finite Element Method simulation, the crack opening loads of different crack lengths are calculated individually instead of plastic wake calculation behind crack tip with node releasing technique, which will save a lot of calculating time. Afterwards the fatigue life under cyclic compression is predicted based on new fatigue crack growth rate curve model for cyclic compression. Meanwhile the analytical method is an engineering estimation for fatigue crack growth under constant amplitude compression. In this method, the crack opening load is estimated based on the symmetry of compression and tension. Then the fatigue life under cyclic compression is also predicted based on a new model for cyclic compression. Finally, fatigue life prediction of a double edged specimen under cyclic compressive loading is taken for example to illustrate the analysis procedure of two simplified methods. By comparing the predicted results with the test data, it is found that the a-N curve and final crack length by two methods are in good agreement with the test data, so the Finite Element Method and analytical method are reasonable and feasible for fatigue crack growth prediction of deepwater structure under cyclic compression.

Biomechanical in vitro comparison of radiofrequency kyphoplasty and balloon kyphoplasty.

Balloon kyphoplasty (BK) has emerged as a popular method for treating osteoporosis vertebral compression fractures (OVCFs). In response to several shortcomings of BK, alternative methods have been introduced, among which is radiofrequency kyphoplasty (RFK). Biomechanical comparisons of BK and RFK are very sparse. The purpose of this study was to perform a biomechanical study in which BK and RFK are compared. Each of the two study groups comprised six specimens prepared from two functional spinal units (FSUs) cut from fresh-frozen cadaveric spines (3 of T9-T11 and 3 of T12-L2). VCFs (A1.2 type) were created in the middle VB of each of the FSUs, with a height loss of 30% of the VB. After that, the specimens were subjected to cyclic compression-compression loading. The following parameters were determined: range of motion (ROM), height of the middle VB, augmentation time, cement interdigitation and cement distribution. Also, the cement layer, the trabecular bone in the augmented VB and the bone-cement interface were examined for cracks. All of these parameters were determined at various stages, namely in the intact middle VB and after its fracture, cement augmentation and subject to the cyclic loading protocol. Fractures caused a significant increase in median ROM and a significant reduction in the height of fractured VB. Cement augmentation significantly stabilized the fractures and led to partial height restoration. ROM and vertebral height, however, were not restored to the intact levels. Cyclic loading led to a further significant increase in ROM and a significant height reduction. There were no significant differences between BK and RFK in terms of any of these parameters. BK and RFK achieved similar results for fracture stabilization and restoration of the height of the fractured VB. RFK involved shorter cement augmentation time and less damage to the trabecular bone.

Compression-compression fatigue behavior of CuZr-based bulk metallic glass composite containing B2 phase

The fatigue behavior of Cu47.5Zr48Al4Co0.5 bulk metallic glass composite (BMGC) containing B2 phase was investigated under uniaxial compression-compression loading modes at 80 Hz with a 0.1 R ratio. The Cu46.5Zr46.5Al7 bulk metallic glass (BMG) was selected as a reference materials. It was found that the BMGC exhibits a lower fatigue limit (1300 MPa) than that of its reference BMG (1500 MPa), which is due to the lower yield strength of the BMGC. The fatigue limit is characterized by the stress range, σr=(σmax-σmin), where σmin and σmax are the applied minimum and maximum stresses, respectively. However, the fatigue ratio (the maximum stress range/yield strength) of the BMGC is higher than that of the BMG, because the “blocking effect” and “martensitic transformation effect” of B2 phase can effectively impede the propagation of fatigue crack and enhance the yield strength of the BMGC. Briefly, B2 phases can obviously improve the fatigue ratio of the CuZr-based BMGCs and thus improve its fatigue behavior, though it can not improve its fatigue limit.

The Stress-Strain Behaviors of High Density Aluminum Foam under Monotonic and Cyclic Loading

The stress-strain behaviors were investigated by monotonic and cyclic stressing tests for high density aluminum foam at room temperature. The cyclic accumulations of deformation for the material were measured in varied loading levels. The effects of mean stress and stress ratio on the ratcheting strain were discussed. The experimental results show that tension response is different from the compressive response. There is obvious cyclic accumulations of deformation (i.e., ratcheting effect) under compression-compression cyclic loading even if the holistic stress-strain response is linear. And the ratcheting of aluminum foam greatly depends on mean stress and stress ratio in asymmetric stress cycling. The experimental rules and data are significant for constitutive description and numerical simulation of aluminum foam.

A New S-N Curve Model of Fiber Reinforced Plastic Composite

Based on an amount of fatigue experimental data of fiber reinforced plastic composite, a new three-parameter S-N curve model is proposed to describe the relationships between the loads and fatigue life under constant amplitude cyclic loading. As the logistic curve behaves as sigmoidal which is the similar with previous S-N models, and from this comparability, an S-N equation with logistic’ form has been established. The model can assess the fatigue behaviors of FRP under various loading conditions, such as, tension-tension (T-T), tension-compression (T-C) or compression-compression (C-C) loading under different stress ratios of the whole region of fatigue life. Several examples are employed to illustrate that the model has ability to fit several different sets of experimental data accurately.

Assessment of Quasi-Static and Fatigue Loaded Notched GRP Laminates Using Digital Image Correlation

This paper presents the results of an experimental study carried out to assess the effects of cumulative damage on the strain response of open-hole (notched) quasi-isotropic [45/0/-45/90]4s E-glass/913 epoxy laminate specimens under quasi-static tension, and constant amplitude tension-tension, compression-compression and tension-compression cyclic loading conditions. In-plane surface strain was measured as a function of applied load and loading cycles for quasi-static and cyclic loading respectively using digital image correlation (DIC) and compared with strain gauge, fibre Bragg grating (FBG) optical sensor and contact extensometer strain measurements. DIC proved successful in monitoring local (near the hole) and global strains, providing critical information on the changes in strain distribution resulting from damage formation and growth incurred.

J0401-2-4 数種のボンドコート上にプラズマ溶射した水酸アパタイトコーティング材の疲労損傷(生体材料およびその表面改質材(2))

This paper describes the fatigue behaviors of coating composites that possesses pure titanium substrates and plasma-sprayed hydroxyapatite and titanium powder coatings. Number of cracks on the cross-section of coating in tension-tension loading is larger than that in compression-compression loading. Acoustic emission signals is also observed and these results shows the clear correlation between the total event count of AE signals and fatigue lives. The best condition of coatings, showed the least counts of AEs, is hydroxyapatite top coat and hydroxyapatite/titanium powders bond coat, each of which has 100 μm thickness.

The Influence of Residual Stresses on the Fatigue Strength of Cold-Formed Structural Tubes

Abstract Rectangular hollow sections (RHS) are widely used in load-carrying structures due to their good load transfer behavior and aesthetic form. During fabrication of a cold-formed rectangular hollow section (CFRHS), the concave inside corner surfaces experience significant compressive plastic strains. The resulting tensile residual stresses in the corner region significantly reduce the fatigue strength in some design applications. Sections cut from CFRHSs with two different wall thicknesses were studied using distortion fatigue loading and using X-ray diffraction residual stress measurements. Residual stresses and fatigue strengths were virtually identical for the two thicknesses even though the corner radius to thickness ratio was different. Residual stresses were found to significantly influence those corners subjected to compression-compression loading. Fatigue strength of these corners was improved by a stress relief heat treatment, but the treatment had no significant effect on corners subjected to tension-tension loading.

A Simple Fatigue Life Model for Three-dimensional Fiber-Polymer Composites

A simple model is proposed for predicting the fatigue life of three-dimensional (3D) fiber-polymer composite materials for certain cyclic load conditions. The fatigue life can be easily calculated using the model with three empirically determined constants: (i) the ultimate strength of the 3D composite, (ii) the ultimate strength of the two-dimensional (2D) laminate, which is identical in every respect to the 3D composite (e.g., same fiber layup pattern, fiber volume content) except for the through-thickness reinforcement, and (iii) the slope parameter (m) of the fatigue-life (S-log N) curve for the 2D laminate. It is shown that the S-log N curves for stitched composites under cyclic tension-tension and compression-compression loading and for z-pinned composites under cyclic bending loading can be accurately predicted using this model. This model can also approximate the tensile fatigue life of composite lap joints reinforced by stitches or z-pins. However, the model is not reliable in predicting the fatigue life of 3D composites in all cases. It is only accurate when the fatigue damage mechanisms and failure mode of the 3D composite are not altered significantly by the through-thickness reinforcement. Consequently, a limitation of the model is that a priori knowledge of the fatigue damage process of the 3D composite is needed before it can be used with confidence to predict fatigue life. This problem is exasperated by the paucity of information available on the fatigue mechanisms of many types of 3D composites. Until this problem is resolved, the model should only be applied to those types of 3D composites in which their fatigue processes have been determined.

Efecto de segundas fases no metálicas sobre el comportamiento a fatiga de componentes de acero con elevadas solicitaciones

To assess the real effect of the inclusion type on fatigue life of ultra clean high strength steels mechanical components made of l00Cr6 steel were fatigue tested and fracture surfaces analysed to determine the origin of fatigue cracks. Two heats proceeding from different steelmaking routes were taken for the tests. The material were forged into ring shape components which were fatigue tested under compression-compression loads. Failures were analysed by SFEM (Scanning Field Emission Microscopy), proving that most of failures at high loads were originated by manganese sulphides of small size (10-70 microns), while less than 40% of all fatigue cracks due to inclusions were caused by titanium carbonitrides and hard oxides. It has been demonstrated that once number and size of hard inclusions have been reduced, the hazardous effect of oxides and carbonitrides on the fatigue life decreases also. However, softer inclusions as manganese sulphides, currently considered as less hazardous, play a more relevant role as direct cause of fatigue failure and they should be taken into account in a deeper way in order to balance both machinability and fatigue life requirements in high strength steel components. Keywords Fatigue. Non-metallic inclusions. MnS. Bearing steel. 100Cr6

Fatigue and fracture behavior of bulk metallic glass

Tensile, compressive, cyclic tension-tension, and cyclic compression-compression tests at room temperature were systematically applied to a Zr52.5CU17.9Al10Ni14.6Ti5 bulk metallic glass for comprehensive understanding of its damage and fracture mechanisms. Under tensile loading, the metallic glass only displays elastic deformation followed by brittle shear fracture. Under compressive loading, after elastic deformadon, obvious plasticity (0.5 to 0.8 pct) can be observed before the final shear fracture. The fracture strength under compression is slightly higher than that under tension. The shear fracture under compression and tension does not occur along the maximum shear stress plane. This indicates that the fracture behavior of the metallic glass does not follow the Tresca criterion. The fracture surfaces show remarkably different features, i.e., a uniform vein structure (compressive fracture) and round cores coexisting with the radiating veins (tensile fracture). Under cyclic tension-tension loading, fatigue cracks are first initiated along localized shear bands on the specimen surface, then propagated along a plane basically perpendicular to the stress axis. A surface damage layer exists under cyclic compression-compression loading. However, the final failure also exhibits a pure shear fracture feature as under uniaxial compression. The cyclic compression-compression fatigue life of the metallic glass is about a factor of 10 higher than the cyclic tension-tension fatigue life at the same stress ratio. Based on these results, the damage and fracture mechanisms of the metallic glass induced by uniaxial and cyclic loading are elucidated.

On static and fatigue strength determination of carbon fibre/epoxy composites Part 1: Experiments

This work seeks to investigate the static and fatigue properties and the failure mechanisms of T300/QY8911 carbon-fibre-reinforced composite laminates with different layups to optimize the stacking sequence effect. Three different layups have been studied, namely, [45/02/-45/902/-45/0/45/90]s, [45/-45/0/-45/0/45/90/45/0/-45]s and [45/0/-45/0/-45/0/45/0/90/0]s. The results for static strength and fatigue residual strength under different fatigue stress amplitudes are evaluated and compared with each other. The damage and failure mechanisms of the composite laminates are discussed. It is observed that all tension-tension fatigue damage patterns of the notched laminates are similar while the tension-tension fatigue properties vary with the laminate layup. The reduction of stress concentration caused by the tension-tension fatigue damage leads to an improvement of the residual strength of the notched specimens in contrast to their static strength properties. The damage mechanics of the notched laminates under compression-compression loading are more complex than those of the tension-tension fatigue specimens; their damage patterns are influenced by the test clamping fixture, the layup, the size of specimens and the diameter of the hole. The residual strengths are lower than those of the specimens without fatigue damage. It is verified that in a high-temperature and moisture environment, there is a decrease in static compression strength. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of a strain-based residual strength model.

Fatigue Issues of Polymeric Foam Sandwich Core Materials in Simple Shear

Obtaining the fatigue properties of sandwich core materials is a particularly difficult issue. This work evaluates the ASTM C 394 test procedure for determining the fatigue properties of core materials using compression-compression loading. The stress concentration at the ends of the specimen where the specimen meets the fixture has been suggested to lead to premature failures. A geometric optimization of specimen ends was attempted to minimize the effects of the stress concentration. This resulted in removing a circular arc of material from the specimen ends. While this allowed the stress concentration to be shifted away from the corner interface of the specimen and fixture, it did not seem to positively influence the fatigue life for the load levels tested. Fatigue results obtained using the compression-compression loading compared well with data obtained using other test methods, including four-point bending. This suggested that the current ASTM C 394 test standard, when used with compression-compression loading, allows acceptable fatigue data to be obtained for foam core materials.