Ultimate Tensile Strength Of Material Research Articles

On the fatigue strength of 3D-printed polylactide (PLA)

This paper aims to review quantitatively our understanding of the fatigue behavior of additively manufactured (AM) polylactide (PLA). A number of data sets were selected from the technical literature and statistically re-analyzed in terms of S-N curves to define a reference value both for the negative inverse slope and the endurance limit extrapolated at 2·106 cycles to failure. The experimental results being post-processed suggest that, as far as AM PLA is concerned, the mean stress effect in fatigue can be modelled by simply using the maximum stress in the cycle. Further, since the printing direction appears to have little effect on the overall fatigue behavior of AM PLA, the stress/strength analysis can be performed effectively by treating this polymer as a homogenous, isotropic and linear-elastic material. According to the statistical re-analysis discussed in the present paper, when appropriate experimental results cannot be generated, the fatigue assessment (for a probability of survival larger than 95%) can be performed by using a reference fatigue curve with negative inverse slope equal to 5.5 and endurance limit (at 2·106 cycles to failure) equal to 10% of the material ultimate tensile strength.

Explosion welding of Al + Cu bimetallic joints for electrical contacts

The manufacture of aluminium + copper electrically conducting bimetallic materials for electrical contacts and adapters by explosion welding was investigated. It is shown that the damping layer can be used efficiently for the protection of the surface of the flyer plate in the manufacture of the M1 + AD1 bimetal. The conditions of explosion welding of the bimetal using an explosive substance consisting of a mixture of porous ammonium nitrate with diesel fuel at a ratio of 96:4 are investigated. The effect of the structure on the physical and mechanical characteristics of the bimetallic material (ultimate tensile strength, shear and bending resistance, specific electrical conductivity) is studied.

Measuring fracture toughness in biological materials.

Many biological materials fail by cracking. Examples are bone fractures, contact damage in eggs, splits in bamboo culm and defects in cartilage. The mechanical property that best describes failure by cracking is fracture toughness, which quantifies the ease with which cracks propagate and defines a material's tolerance for pre-existing cracks and other stress concentrating features. The measurement of fracture toughness presents some challenges, especially for biological materials. To obtain valid results requires care and, in many cases, considerable ingenuity to design an appropriate specimen and test protocol. Common mistakes include incorrect interpretation of the mechanics of loading in unusual specimen designs, and failures occurring at the material's ultimate tensile strength as a result of specimens or cracks being too small. Interpretation of the resulting toughness data may also present challenges, for example when R-curve behaviour is present. In this article, examples of good and bad practice are described, and some recommendations made.

Acoustic emission analysis for characterisation of damage mechanisms in glass fiber reinforced polyester composite

This study assesses the progression of damage occurring on glass fiber reinforced polyester composite specimens using acoustic emission (AE) parameters. Its aims are to improve understanding of the particular characteristics of AE signals; and also to determine the relationship between AE signals and the failure of the material. Time and frequency domain trends were analysed at four different applied loads (60.97, 67.75, 74.52 and 81.30 MPa) representing 45–60% of the ultimate tensile strength of material. The relevant AE parameters were analysed both in the early stages of the test and as the material neared the fracture zone. The results showed a high degree of correlation between the root mean square and number of hits AE values and the number of cycles to failure, of 92.99 and 92.19%, respectively. This correlation, as well as AE basic parameters, suggests that AE can be a valuable tool to predict the fatigue life and detect the onset of damage in such composite materials.

Time domain series system definition and gear set reliability modeling

Time-dependent multi-configuration is a typical feature for mechanical systems such as gear trains and chain drives. As a series system, a gear train is distinct from a traditional series system, such as a chain, in load transmission path, system-component relationship, system functioning manner, as well as time-dependent system configuration. Firstly, the present paper defines time-domain series system to which the traditional series system reliability model is not adequate. Then, system specific reliability modeling technique is proposed for gear sets, including component (tooth) and subsystem (tooth-pair) load history description, material priori/posterior strength expression, time-dependent and system specific load-strength interference analysis, as well as statistically dependent failure events treatment. Consequently, several system reliability models are developed for gear sets with different tooth numbers in the scenario of tooth root material ultimate tensile strength failure. The application of the models is discussed in the last part, and the differences between the system specific reliability model and the traditional series system reliability model are illustrated by virtue of several numerical examples.

Mechanical Properties of Hemp (Cannabis Sativa) Biomass

In Latvia approximately of 14.6% of unfarmed agricultural land can be used for herbaceous energy crop growing. Herbaceous energy crops would be as the main basis for solid biofuel production in agricultural ecosystem in future. Herbaceous energy crops as hemp (Cannabis sativa) are grown in recent years and can be used for solid biofuel production. Experimentally stated hemp stalk material ultimate tensile strength the medium value is 85 ± 9 N mm-2. The main conditioning operation before preparation of herbaceous biomass compositions for solid biofuel production is shredding. Therefore hemp stalks were used for cutting experiments. Cutting using different types of knives mechanisms had been investigated. Specific shear cutting energy for hemp samples were within 0.02 – 0.04 J mm-2. Hemp stalk material density was determined using AutoCAD software for cross-section area calculation. Density values are 325 ± 18 kg m-3 for hemp stalks. Specific cutting energy per mass unit was calculated on basis of experimentally estimated values of cutting energy and density.

The Theory of Critical Distances to Model the Short- to Long-crack Transition in Geological Materials Subjected to Mode I Static Loading

The Theory of Critical Distances postulates that, in cracked materials subjected to static loading, breakage takes place when a distance dependent effective stress exceeds the material tensile strength. Such an effective stress is equal to the stress calculated either at a certain distance from the notch tip (Point Method), averaged over a line (Line Method), over an area (Area Method) or, finally, averaged in a finite volume (Volume Method). The necessary characteristic length is a material property which can directly be determined by combining the material ultimate tensile strength with the plane strain fracture toughness. In the present investigation, by re-analysing a large number of experimental results taken from the literature, it is shown that the Theory of Critical Distances is successful in modelling the transition from the short- to the long-crack regime in geological materials subjected to Mode I static loading.

Comparison of material properties: Steel 20MnCr5 and similar steels

Starting from the fact that the experimental data are real data, and that the assessment of their values is of great importance in a design of the structure, this article seeks to draw attention to the designers of experimental data related to steel 20MnCr5 (1.7147, AISI 5120). In this sense, this paper presents the experimental results involving material ultimate tensile strength, yield strength, creep behavior, total fracture strain, reduction in the area as well as Charpy impact energy. All of the mentioned tests were conducted at room temperature and at elevated temperatures. Considerable tensile testing referring to determination of ultimate tensile strength as well as 0.2 offset yield strength resulted in engineering stress–strain diagrams, while those tensile testing regarding creep behavior resulted in creep curves. Also, modeling of material creep behavior using rheological models and an equation proposed by the authors can be found in this paper. Using Charpy impact energy tests, an assessment of fracture toughness was made. In addition to this, the paper presents a comparison of the material properties of 20MnCr5 steel with material properties of other similar (structural/constructional) steels.

Effect of Preheating and Post-Curing Time on the Mechanical Properties of Epoxy Resin

The purpose of this study is to compare the mechanical properties in the form of ultimate tensile strength, ultimate tensile strain and Young's modulus of an epoxy resin at different curing cycles. The work carried out consisted of investigating the effect of preheating time and then the effect of post-curing time at the same temperature. Five repeats of static tensile tests were then carried out using universal test machine. Results indicated that compared to a shorter epoxy resin preheat duration of 15 min at 80°C, a longer duration of 30 min at 80°C of preheating degrades the material ultimate tensile strength and ultimate tensile strain leading to a suffer material. However, compared to no further post-curing of the epoxy resin, a two-hour post-cure duration at 80°C slightly increased the ultimate tensile strength and significantly decreased the ultimate tensile strain making the material even suffer than in the case of preheating. The implication is that in-house cure cycle tests should be carried out to characterize the resin instead of exclusively relying on resin manufacturer proposed cure cycles.

Tensile strength and failure simulation of simplified spot weld models

A simple model for spot weld joints is desirable in body-in-white automotive structures which contains thousands of them. Hence, comparative performance and failure prediction study of six simplified spot weld models in terms of their geometric and constitutive properties are presented in this paper. The stiffness characteristics of these models under tensile loading condition were compared with the experimental results. It was found that the current spot weld modelling practice in the automotive industry predict the strength with 45.33% of error. To simulate the joint failure a material damage criterion correlating ultimate tensile strength of material was implemented in the developed models. The comparative study with respect to the accuracy was also related with the computational cost incurred by the different models. Hence, suitable modelling conditions to design a finite element model for spot welded joints are established which is very simple to develop, relatively cheap in terms of computational costs but yet predicts reasonably accurate results.

On the estimation of the material fatigue properties required to perform the multiaxial fatigue assessment

ABSTRACTTo accurately perform the fatigue assessment of engineering components subjected to in‐service multiaxial fatigue loading, the adopted design criterion must properly be calibrated, the used information usually being the fatigue strength under both pure uniaxial and pure torsional fatigue loading. Because of the complex fatigue response of metallic materials to multiaxial loading paths, the only reliable way to generate the necessary pieces of calibration information is by running appropriate experiments. Unfortunately, because of a lack of both time and resources, very often, structural engineers are requested to perform the multiaxial fatigue assessment by guessing the necessary fatigue properties. In this complex scenario, initially, the available empirical rules suitable for estimating fatigue strength under both pure axial and pure torsional fatigue loading are reviewed in detail. Subsequently, several experimental results taken from the literature and generated by testing metallic materials under a variety of proportional and non‐proportional multiaxial loading paths are used to investigate the way such empirical rules affect the accuracy in estimating fatigue strength, the damage extent being evaluated according to the modified Wöhler curve method. Such a systematic validation exercise allowed us to prove that under proportional loading (with both zero and non‐zero mean stresses), an adequate margin of safety can be reached even when the necessary calibration information is directly estimated from the material ultimate tensile strength. On the contrary, in the presence of non‐proportional loading, the use of the empirical rules reviewed in the present paper can result, under particular circumstances, in a non‐conservative fatigue design.

Gradient enriched linear-elastic crack tip stresses to estimate the static strength of cracked engineering ceramics

According to Gradient Mechanics (GM), stress fields have to be determined by directly incorporating into the stress analysis a length scale which that takes into account the material microstructural features. This peculiar modus operandi results in stress fields in the vicinity of sharp cracks which are no longer singular, even though the assessed material is assumed to obey a linear-elastic constitutive law. Given both the geometry of the cracked component being assessed and the value of the material length scale, the magnitude of the corresponding gradient enriched linear-elastic crack tip stress is then finite and it can be calculated by taking full advantage of those computational methods specifically devised to numerically implement gradient elasticity. In the present investigation, it is first shown that GM’s length scale can directly be estimated from the material ultimate tensile strength and the plane strain fracture toughness through the critical distance value calculated according to the Theory of Critical Distances. Next, by post-processing a large number of experimental results taken from the literature and generated by testing cracked ceramics, it is shown that gradient enriched linearelastic crack tip stresses can successfully be used to model the transition from the short- to the long-crack regime under Mode I static loading.

Effect of correlated input parameters on the failure probability of pipelines with corrosion defects by using FITNET FFS procedure

The paper presents a probabilistic methodology considering the correlations between the input variables for the failure probability evaluation of corroding pipelines based on the corrosion module of the FITNET FFS procedure. A computer program based on this method is developed to calculate the failure probability of pipelines by considering different numbers of defects and different elapsed times. In case of one defect, the correlation between the initial defect depth and the initial defect length has the most significant impact on the failure probability of the pipeline. If the correlations between these two parameters for an individual defect are not considered, the prediction results are nonconservative when the failure probability is below 40% and conservative when it is above 40%. In case of multiple defects, the independent assumption of variables generally leads to a conservative estimate of the failure probability. The conservatism increases if the elapsed time and/or the actual correlation coefficients of the variables increase. The correlation of the operating pressure, the initial defect depth and material ultimate tensile strength at the location of different defects has a larger impact on the failure probability than the correlation of other parameters at different defects. The upper bound failure probability calculated by engineering method corresponds to that calculated using the presented method without considering the correlation between input parameters. This confirms the validity of the presented model.

Finite Element Analysis of Diesel Engine Cylinder Head Stress and Deformation with Thermal-Mechanical Coupling

Considering the structure of some diesel engine cylinder head, its 3-D solid model and the finite element model is built, and after the load and constraint of is deal with, the stress and deformation the cylinder head with thermal-mechanical coupling is calculated with FEA ( Finite Element Analysis) software ABQUS. Analysis results find that: (1) the first main stress maximum value of cylinder head is up to 199.6MPa, which is less than 250MPa of the HT250 material ultimate tensile strength; (2) the deformation area is mainly in the flame face surface and fuel injector coxcombing, and the deformation of flame face is general symmetrical broadways and slightly large near the exhaust passage longways, while the deformation of fuel injector coxcombing is general symmetrical broadways and longways; (3) the structure design and strength of the cylinder head satisfy the design requirements.

Contact pressure evolution and its relation to wear in sheet metal forming

For a given sheet metal forming process, an accurate determination of the contact pressure distribution is an essential step towards the estimation of tool life. This investigation utilizes finite element (FE) analysis to model and explain the evolution and distribution of contact pressure over the die radius, throughout the duration of a channel forming process. It was found that a typical two-peak steady-state contact pressure response exists for the majority of the process. However, this was preceded by an initial transient response, characterized by extremely large and localized contact pressures, which were more than double the magnitude of the steady-state peak pressure. The validity of the predicted contact pressure behavior was assessed via detailed numerical analysis and by examining the wear response of an experimental stamping operation. The experimental results revealed that the high contact pressure zones of the transient response corresponded to a severe galling wear mechanism. Therefore, the transient response may be of primary significance to the tool wear response; thus questioning the applicability of traditional bending-under-tension wear tests for sheet metal stamping processes. Finally, a parametric study was conducted, examining the influence of the major process parameters on the steady-state and peak transient contact pressures, using the developed FE model. It was found that the bend ratio and the blank material ultimate tensile strength had the most influence on the peak contact pressures. The main process-related parameters, friction coefficient and blank holder force, were found to have only a minor influence.

Work-piece length of the effect on stress and analysis of cracking-criterion under equal channel angular pressing

Finite-element method (FEM) and experimental investigation of 2024 Al subjected to equal-channel angular pressing (ECAP) has been carried out. The maximum equivalent normal stress and the maximum shear stress at an optionally given displacement of ECAP have been obtained through FEM for various given initial length of ECAP samples. The cracking criterion for the materials subjected to ECAP is further discussed with the help of experimental investigation. It is observed that at all given displacement of ECAP, the maximum equivalent normal stress is always less than the ultimate tensile strength of materials for all ECAPed samples with various initial length, while the maximum shear stress is always present at the angular channel zone of ECAP die, and its value decreases with the decrease of initial length of ECAPed samples. When the used initial length is small enough, the computed maximum shear stress becomes less than the shear strength of the materials, which is in very good agreement with the experimental observation that the frequency of sample cracking is decreased greatly. It is concluded that the non-cracking criterion of the materials subjected to ECAP could be expressed as "the maximum shear stress is less than the shear strength of materials". It is also suggested that a rational research should be involved in the actual measurement of stress-strain curve and the optimization in the configuration of ECAP die, the technology of materials pretreatment and the length of samples based on the above-motioned non-cracking criterion.

A critical distance study of stress concentrations in bone

The Theory of Critical Distances (TCD) is a method used to study the failure of material in situations where stress concentrations, such as holes and notches, are present. This method uses two material constants: a critical length and a critical stress. The elastic stress field close to the stress concentration is examined, applying a fracture criterion. The TCD has been applied to predict brittle fracture in various different materials and various types of notches but it has not previously been applied to bone. Since bone fails by brittle fracture with limited plasticity, it is expected that the TCD will be applicable. Experimental data were obtained from the literature on the effects of sharp notches and holes loaded in various ways (tension, torsion and bending). These tests were modelled using finite element analysis. It was found that the TCD could be successfully applied to predict the load required for brittle fracture as a function of the type and size of the stress concentration feature. The critical distance was found to be almost constant, about 0.3–0.4 mm, for all types of bone studied: the critical stress was found to be related to the material's ultimate tensile strength by a constant factor of T=1.33. The results of this study will be of practical value in the assessment of stress concentration features introduced during surgery and of naturally occurring bone defects.

Improving friction stir welding of blanks of different thicknesses

Friction stir welding (FSW) appears to be a promising process even in the welding of blanks of different thicknesses. Actually, such particular tailor welded blanks (TWBs) are usually characterized by a reduction in ductility due to the utilized fusion welding process. In this paper the authors, starting from a preliminary feasibility study, investigate the possibility to improve the mechanical performances of friction stir welded blanks of aluminum alloy with different thicknesses. Both experiments and a FE analyses are developed for a few case studies with different thickness ratios between the blanks. The numerical investigations are performed with the aim to highlight the material temperature distribution during the process in order to determine process conditions for which an almost symmetric thermal flow is obtained in the two blanks of the joint. In this way, a few simple process design rules are derived and verified through experiments. In particular a thickness ratio up to 2 was considered and a joint resistance of about the 80% of the parent material ultimate tensile strength was observed.

Discrete element method for modelling solid and particulate materials

AbstractThe discrete element method (DEM) is developed in this study as a general and robust technique for unified two‐dimensional modelling of the mechanical behaviour of solid and particulate materials, including the transition from solid phase to particulate phase. Inter‐element parameters (contact stiffnesses and failure criteria) are theoretically established as functions of element size and commonly accepted material parameters including Young's modulus, Poisson's ratio, ultimate tensile strength, and fracture toughness. A main feature of such an approach is that it promises to provide convergence with refinement of a DEM discretization. Regarding contact failure, an energy criterion based on the material's ultimate tensile strength and fracture toughness is developed to limit the maximum contact forces and inter‐element relative displacement. This paper also addresses the issue of numerical stability in DEM computations and provides a theoretical method for the determination of a stable time‐step. The method developed herein is validated by modelling several test problems having analytic solutions and results show that indeed convergence is obtained. Moreover, a very good agreement with the theoretical results is obtained in both elastic behaviour and fracture. An example application of the method to high‐speed penetration of a concrete beam is also given. Copyright © 2006 John Wiley & Sons, Ltd.

Effect of Boundary Conditions of Failure Pressure Models on Reliability Estimation of Buried Pipelines

This paper presents the effect of boundary conditions of various failure pressure models published for the estimation of failure pressure. Furthermore, this approach is extended to the failure prediction with the help of a failure probability model. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with each corrosion defect in buried pipelines for long exposure periods with unit of years. The effects of random variables such as defect depth, pipe diameter, defect length, fluid pressure, corrosion rate, material yield stress, material ultimate tensile strength and pipe thickness on the failure probability of the buried pipelines are systematically investigated for the corrosion pipeline by using an adapted failure probability model and varying failure pressure model.