Conventional Mechanical Testing Research Articles

Failure analysis of an offshore drilling casing under harsh working conditions

An N80 casing in a certain oil well was broken. After the casing was pulled out, many cracks, sand holes, and corrosion and rust marks were observed in the casing fracture. To test the cause of the fracture, failure simulation using ANSYS software was carried out. Metallographic analysis test, chemical composition analysis test, and conventional mechanical performance test of the casing body were designed, and finally the failure analysis of the casing fracture was completed. The results revealed several large-scale oxide metallurgical inclusions in the casing near the upper end of the wellhead, which reduced the strength of the casing material and caused the casing to crack at the maximum stress position. In addition to harsh service environment, the casing was subjected to strong stress, which exceeded the strength limit of the casing and eventually caused the casing to break. The casing material met the standard requirements at all parts except the fracture areas. A calculation method is proposed for the ocean current and wind force; the method has high accuracy and can be used for analyzing similar offshore conditions. To prevent accidents, it is recommended to strictly control the heat treatment process of the casing material, optimize its microstructure, test its performance before deployment, and establish a real-time analysis system. Timely adjustments should be made to the operating schedule when operating in harsh environments.

Optimization on the Johnson-Cook parameters of Ti-6Al-4V used for high speed cutting simulation

The Johnson-Cook (J-C) parameters obtained from the conventional mechanical tests are usually adopted directly for the high-speed cutting simulations. However, the conventional J-C parameters can not describe the exact plastic deformation under the coupling effect of large strain and high strain rate occurred in high speed cutting. In this paper, the response surface approximation method was used to optimize the Ti-6Al-4V’s J-C parameters for high speed cutting simulation, and the experimental results obtained from our previous work were further adopted to validate the optimized parameters. The simulated chip size error obtained at the cutting speed of 15 m/s could reduce from 16% with using the conventional J-C parameters to 8% with using the optimized J-C parameters. Furthermore, the simulated chip morphologies achieved based on the optimized J-C parameters were compared with the experimental results with cutting speed ranging from 0.05 m/s to 86.5 m/s. The results show that the simulated chip morphologies could give good agreements with the experimental results, and the chip morphology transitions can be well predicted with using the optimized J-C parameters.

Deformation mechanisms during continuous cooling compression of WE54 magnesium alloy

A great potential is opening up for WE grade magnesium alloys to be used in industrial applications. To design a proper thermomechanical process, toward yielding an optimized mechanical properties, it is crucial to develop a deep understanding of dominant deformation mechanisms. The contribution of different deformation mechanisms complicates the knowledge on the deformation behavior of WE grade magnesium alloys. Moreover, the results gathered from conventional mechanical testing are applicable only to a certain initial microstructure. In this work, continuous cooling compression testing method was employed to study the flow behavior and active deformation mechanisms in a WE magnesium alloy at a wide temperature range of 550 to 200 °C. The critical points on the true stress-temperature curve were determined and then discussed relying on the microstructural observations. The results implied that precipitation of second phase particles and accompanying flow hardening may occur in two stages at 525 and 360 °C, while dynamic recrystallization and related work softening was observed at 435 °C. During the continuous cooling deformation route, the transition of dominate deformation mechanism from slip to twinning was identified to take place at 300 °C. Moreover, a secondary work hardening effect owing to twinning was recognized at 250 °C, which was explained by Basinski-type hardening arising from transmutations of dislocations.

Benchmark study of undrained triaxial testing of Opalinus Clay shale: Results and implications for robust testing

Triaxial testing of argillaceous rocks and shales is significantly more challenging than conventional rock mechanical testing. The challenges are mainly related to the very low permeability of these geomaterials, and their sensitivity to exposure of atmosphere and brines, which induces variations of water content, suction and effective stress. There are currently no international standards to guide service laboratories for robust testing procedures for shales. A benchmark study of undrained triaxial testing was therefore initiated with three leading service laboratories in shale testing, performing 13 tests and using two different methods of establishing sample saturation prior to deformation. Both methods paid particular attention to minimize volume expansion of the specimens during saturation, and the loading rate during the shear phase in all tests was selected based on intrinsic sample properties and drainage configurations to ensure pore fluid pressure equilibration across the specimen. Opalinus Clay shale core material from the Mont Terri underground research laboratory was used for testing specimens, and intervals on cores were pre-selected on the basis of computer tomography to minimize material heterogeneity. A detailed diagnostic analysis of all tests was performed, and a comparison of the testing results is presented. Good reproducibility of the effective stress paths was achieved by the different laboratories for tests at identical or near-identical initial effective stress conditions. In particular, the test results over a larger range of effective stresses indicate very similar evolution of the fluid pressure during testing and a consistent picture for the derivation of global material properties. On the example of Opalinus Clay, the study demonstrates that robust triaxial testing results can be achieved for shales if some key challenges are adequately addressed.

Temperature Dependence of Elastic–Plastic Properties of Fine-Pitch SAC 0307 Solder Joint Using Nanoindentation Approach

This paper highlights the advantages of using the nanoindentation approach over the conventional method for the mechanical characterization of components used in electronic packaging. The limitation of the conventional method has become more critical with the miniaturization of electronic packages, giving inadequate information regarding the mechanical properties of metallurgical interconnections. The load–displacement approach via nanoindentation was used in this study to determine the micromechanical properties of a fine-pitch solder joint subjected to aging for 1000 hours. This approach is more advantageous than tensile testing, as it focuses on the elastic behavior unlike that in conventional mechanical testing. The nanoindentation analysis results showed that the elastic–plastic behavior before failure can be assessed in a wide range of temperatures and thus help study the temperature dependence on the mechanical properties of fine-pitch solder joints. The characterization was done beyond the elastic range beforehand of conventional method. The modulus and hardness of the fine-pitch SAC 0307 solder joint decreased while its plastic and elastic behaviors became pronounced at higher aging temperatures. This implies that solder joints become weaker and less resilient with increasing temperature, at least for a duration of 1000 hours.

Characterizing the non-linear mechanical behavior of native and biomimetic engineered tissues in 1D with physically meaningful parameters

It is common practice to evaluate the mechanical performance of a scaffold for tissue engineering using concepts from linear elasticity theory (i.e. Young's modulus), or variations thereof, and uniaxial testing data. In some cases the non-linear nature of tissue stress-strain behavior has prompted development of empirical approaches to obtain a more comprehensive description of the observed mechanical behavior. Such approaches constitute improvements over singular stiffness measures but the lack of an appropriate non-linear theoretical foundation renders them somewhat arbitrary and potentially incomplete. Recently, a constitutive model for non-linear tissues was developed based on first principles in physics. The Freed-Rajagopal 1-D Fiber Model incorporates physically meaningful parameters that provide a unique and comprehensive characterization of non-linear tissue behavior for the class of tissues with strain limiting behavior in 1D. The physical interpretation that these parameters provide suggests they may serve as useful design targets for tissue engineering applications. In this study, the Freed-Rajagopal model is employed with conventional uniaxial mechanical testing data obtained from experiments with collagen scaffolds for hernia repair grafts and the healthy native tissue counterpart. Results from the Freed-Rajagopal analysis revealed that tissue-engineered constructs that qualify as “biomimetic” according to linear elasticity theory, or variations thereof, are not truly biomimetic, as they do not mimic the non-linear mechanical behaviors observed in their native tissue counterparts. Most importantly, the Freed-Rajagopal model was easy to employ (it can be done using a standard uniaxial testing system, with minimal additional effort) and revealed specific design improvements that could be targeted to improve the biofidelity of these constructs. A performance comparison with conventional non-linear models (including Fung's 1D Law and a one-dimensionalized version of the Holzapfel, Gasser, Ogden model), was then conducted and revealed the Freed-Rajagopal model produced results that correlated exceptionally well with experimental data and better describes material behavior at low strains as compared to competing models.

In situ computed tomography for the characterization of the fatigue damage development in glass fiber-reinforced polyurethane

Abstract Fiber-reinforced polymers show a continuous material degradation under cyclic loading, which is why damage development has to be investigated for an exact assessment of fatigue properties. In order to obtain information on damage in the internal volume, conventional mechanical test methods require accompanying support by further developed techniques. In this study, a methodology for in situ computed tomography has been developed and applied to glass fiber-reinforced polyurethane. Polyurethane has advantages over epoxy in terms of impact strength, damage tolerance and abrasion, which are important for various applications. Fatigue properties, on the other hand, are largely unknown. Optimized imaging parameters for computed tomography have been established in order to obtain detailed 3D volume images suitable for analysis. The 3D volumes of the damage state were recorded according to defined fatigue load steps and used to evaluate and correlate the damage development with the mechanical properties. The results confirm known damage characteristics of fiber-reinforced composites but also show material and structure-related differences in crack formation and propagation.

New In Situ Imaging-Based Methodology to Identify the Material Constitutive Model Coefficients in Metal Cutting Process

A great challenge of metal cutting modeling is the ability of the material constitutive model to describe the mechanical behavior of the work material under the deformation conditions that characterizes this process. In particular, metal cutting generates a large range of state of stresses, as well as strains and strain rates higher than those generated by conventional mechanical tests, including the Split-Hopkinson pressure bar tests. A new hybrid analytical–experimental methodology to identify the material constitutive model coefficients is proposed. This methodology is based on an in situ high-resolution imaging and digital image correlation (DIC) technique, coupled with an analytical model of orthogonal cutting. This methodology is particularly suitable for the identification of the constitutive model coefficients at strains and strain rates higher than those found in mechanical tests. Orthogonal cutting tests of nickel aluminum bronze alloy are performed to obtain the strains and strain rates fields in the cutting zone, using DIC technique. Shear forces derived from stress integrations are matched to the measured ones. Then, the constitutive model coefficients can be determined, which is performed by solving a sequential optimization problem. Verifications are made by comparing the strain, strain rate, and temperature fields of cutting zone from experiments against those obtained by finite element simulations using the identified material constitutive model coefficients as input.

Lime putty versus hydrated lime powder: Physicochemical and mechanical characteristics of lime based mortars

The aim of this work is to study the influence of calcium hydrated lime (lime putty or hydrated lime powder) to the chemical and physico-mechanical characteristics of lime mortars. The mortars were designed with the same mixing ratio of lime/aggregates and evaluated till 18 months of curing. The carbonation rate is evaluated via DTA/TG, the pore structure by mercury intrusion porosimetry and the hygric properties via capillary rise and water immersion tests. Mortars’ shrinkage and apparent density were also measured along with mechanical strength and static and dynamic modulus of elasticity that were evaluated by using conventional mechanical tests and ultrasonic technique. The obtained results revealed that lime powder mortars present a higher carbonation rate and higher values of compressive strength compared to lime putty mortars. Lime powder mortars also exhibit a unimodal pore size distribution (while lime putty mortars present a bimodal one) and higher capillary rise coefficient and porosity accessible to water in respect to lime putty mortars.

Advances in Damage Monitoring Techniques for the Detection of Failure in SiCf/SiC Ceramic Matrix Composites

From a disruptive perspective, silicon carbide (SiC)-based ceramic matrix composites (CMCs) provide a considerable temperature and weight advantage over existing material systems and are increasingly finding application in aerospace, power generation and high-end automotive industries. The complex structural architecture and inherent processing artefacts within CMCs combine to induce inhomogeneous deformation and damage prior to ultimate failure. Sophisticated mechanical characterisation is vital in support of a fundamental understanding of deformation in CMCs. On the component scale, “damage tolerant” design and lifing philosophies depend upon laboratory assessments of macro-scale specimens, incorporating typical fibre architectures and matrix under representative stress-strain states. This is important if CMCs are to be utilised to their full potential within industrial applications. Bulk measurements of strain via extensometry or even localised strain gauging would fail to characterise the ensuing inhomogeneity when performing conventional mechanical testing on laboratory scaled coupons. The current research has, therefore, applied digital image correlation (DIC), electrical resistance monitoring and acoustic emission techniques to the room and high-temperature assessment of ceramic matrix composites under axial tensile and fatigue loading, with particular attention afforded to a silicon carbide fibre-reinforced silicon carbide composite (SiCf/SiC) variant. Data from these separate monitoring techniques plus ancillary use of X-ray computed tomography, in-situ scanning electron microscopy and optical inspection were correlated to monitor the onset and progression of damage during mechanical loading. The benefits of employing a concurrent, multi-technique approach to monitoring damage in CMCs are demonstrated.

The Influence of Process Parameters and Build Orientation on the Creep Behaviour of a Laser Powder Bed Fused Ni-based Superalloy for Aerospace Applications.

Additive Layer Manufacturing (ALM) is an innovative net shape manufacturing technology that offers the ability to produce highly intricate components not possible through traditional wrought and cast procedures. Consequently, the aerospace industry is becoming ever more attentive in exploiting such technology for the fabrication of nickel-based superalloys in an attempt to drive further advancements within the holistic gas turbine. Given this, the requirement for the mechanical characterisation of such material is rising in parallel, with limitations in the availability of material processed restricting conventional mechanical testing; particularly with the abundance of process parameters to evaluate. As such, the Small Punch Creep (SPC) test method has been deemed an effective tool to rank the elevated temperature performance of alloys processed through ALM, credited to the small volumes of material utilised in each test and the ability to sample material from discrete locations. In this research, the SPC test will be used to assess the influence of a number of key process variables on the mechanical performance of Laser Powder Bed Fused (LPBF) Ni-based superalloy CM247LC. This will also include an investigation into the influence of build orientation and post-build treatment on creep performance, whilst considering the structural integrity of the different experimental builds.

Characterising the fatigue performance of additive materials using the small punch test

In recent years the use of Additive Manufacturing (AM) has become increasingly widespread with numerous industries now moving towards large scale manufacture of structurally integral components. The nature of AM offers the ability to manufacture more complex and optimised geometries, such as cooling channels and honeycomb structures, which would not be possible or economically viable to manufacture using more traditional fabrication processes. However, the layer by layer build structure of AM components also introduces a complex and component specific microstructure arising from the rapid cooling rates resulting from the build parameters and geometries, which hence influence the mechanical properties. Therefore, the use of conventional mechanical test approaches to assess the performance of these materials can be limited. This paper will extend upon some of the recent research at Swansea University in applying the innovative small punch fatigue (SPF) experiment to characterise the mechanical performance of AM materials and how they compare to traditionally manufactured variants of the same alloys. Results show excellent agreement with the microstructural morphologies of the different materials, with supporting fractography evidencing the contrasting failure modes.

Experimental Investigation on the Effects of Microwave Treatment on Basalt Heating, Mechanical Strength, and Fragmentation

Microwave energy can be used to assist mechanical rock breakage for civil and mining engineering operations. To assess the industrial applicability of this technology, microwave heating of basalt specimens in a multi-mode cavity (a microwave chamber) at different power levels was followed by conventional mechanical strength and fragmentation effect tests in the laboratory. X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy were used to determine the mineral composition and distribution of the basalt, to aid interpretation of crack propagation patterns and the associated strength reduction mechanism. These analyses demonstrated that cracks mainly occurred around olivine grains, primarily as intergranular cracks between olivine and plagioclase grains and intragranular cracks within olivine grains. Strength reduction during microwave fracturing of basalt is driven by heat from enstatite (a microwave-sensitive mineral) and volumetric expansion of olivine (a thermally expansive mineral). Uniaxial compressive, Brazilian tensile, and point load strengths all decreased with increasing microwave irradiation time at rates that were positively related to the power level. For a given power level, mechanical strength reduction can be estimated from linear relationships with irradiation time. On the other hand, a power function best described burst time (the irradiation time at which the specimen burst into fragments) vs. power level (for a given specimen size) and burst time vs. specimen size (for a given power level) relationships. Microwave-induced hard rock fracturing can be an integral part of new methods for rock breakage and tunnel excavation.

Mechanical characterization of the static and fatigue compressive properties of a new glass/flax/epoxy composite material using digital image correlation, thermographic stress analysis, and conventional mechanical testing

This study characterized the static and fatigue compressive properties of a new hybrid composite material made of synthetic and natural fibers with an epoxy matrix. The glass/flax/epoxy composite material was manufactured as a “sandwich structure” with a Type A configuration (i.e. [0G2/0F12/0G2] using unidirectional glass (G) and flax (F) fibers) and Type B configuration (i.e. [0G2/±45F12/0G2] using unidirectional glass (G) and ±45° oblique flax (F) fibers). Digital image correlation was used to obtain the static properties of compressive elastic modulus (Type A, 24.4 GPa; Type B, 14.7 GPa), ultimate compressive strength (Type A, 261.7 MPa; Type B, 231.9 MPa), and Poisson's ratio (Type A, 0.37; Type B, 0.58). Thermographic stress analysis was used to measure a high cycle fatigue strength (HCFS) of 53% (Type A and B) of ultimate compressive strength. Conventional experimental fatigue methods (i.e. stress vs. number of cycles to failure) yielded a HCFS of 56–61% (Type A) and 51–56% (Type B), as well as almost constant dynamic compressive moduli of 15 GPa (Type A) and 10 GPa (Type B) over the entire loading regime. This new composite material may have various potential applications, such as aerospace, automotive, biomechanics, sports, etc., based on the compressive properties measured.

Revisiting the Buckling Metrology Method to Determine the Young's Modulus of 2D Materials.

Measuring the mechanical properties of 2D materials is a formidable task. While regular electrical and optical probing techniques are suitable even for atomically thin materials, conventional mechanical tests cannot be directly applied. Therefore, new mechanical testing techniques need to be developed. Up to now, the most widespread approaches require micro-fabrication to create freely suspended membranes, rendering their implementation complex and costly. Here, a simple yet powerful technique is revisited to measure the mechanical properties of thin films. The buckling metrology method, that does not require the fabrication of freely suspended structures, is used to determine the Young's modulus of several transition metal dichalcogenides (MoS2 , MoSe2 , WS2 , and WSe2 ) with thicknesses ranging from 2 to 10 layers. The obtained values for the Young's modulus and their uncertainty are critically compared with previously published results, finding that this simple technique provides results which are in good agreement with those reported using other highly sophisticated testing methods. By comparing the cost, complexity, and time required for the different methods reported in the literature, the buckling metrology method presents certain advantages that make it an interesting mechanical test tool for 2D materials.

Novel CNTs grafting on carbon fibres through CVD: investigation of epoxy matrix/fibre interface via nanoindentation

Carbon Fibre Reinforced Polymers (CFRPs) have spread to a broad range of sectors including automobile, aeronautics and space industry the last decades. Recently, the emergence of new requirements for improved smart properties and functionalities have been main drivers to the introduction of novel methodologies and optimization of processes. A new approach of functionalizing CFs is the in-situ grafting of carbon nanotubes (CNTs) onto the surface of fibres, through chemical vapour deposition (CVD). In this study, CFRPs were manufactured via Vacuum Assisted Resin Transfer Molding (VARTM) and characterized by microscopy techniques through their cross-section. The effect of CNTs in-situ grafting onto the CFs on the mechanical behavior of the composite was studied both in micro- and macro-scale level, through instrumented indentation technique and tensile testing. The mechanical behaviour of the composite with the CNTs in-situ grafted onto the CFs was compared with CNTs-modified composites, containing CNTs in the epoxy matrix. Comparing the nanomechanical properties with conventional mechanical testing, the enhancement of mechanical behaviour was revealed for the case of the CNTs-modified composite. Additionally, an increased interfacial adhesion between the CNTs-functionalised CFs and the polymer matrix was observed, indicating that CNTs contribute to an enhanced bonding between matrix and CFs.

Variability of Mechanical Properties of Collagen Membranes used in Dentistry

The aim of this study is proposing a combination of measurements to assess the functional variability of collagen membranes used in Guided Bone Regeneration (GBR) and Guided Tissue Regeneration (GTR) techniques. As far as clinical applications are concerned, a proper qualification is critical when deciding, among commercially available collagen membranes, upon the most appropriate one for each specific clinical case. Two commercially available collagen membranes, namely Collprotect� and Jason�, were considered for the experimentation. After thickness and density measurements, the quasi-static behavior was studied for both membranes by means of conventional mechanical tests, i.e. tear and tensile tests, whereas their time-dependent behavior was evaluated by means of stress relaxation tests and dynamic mechanical analysis. Collagen membranes showed an elevated among samples variability. The variability within the same kind of membrane is of the same order of magnitude of the between membrane kinds variability. All the membranes showed strong time dependence both in stress relaxation and in dynamic mechanical tests. This fact should be taken under consideration for the membrane final application.

Effect of CCBP doping on the multifunctional Al-0.5 Mg-15CCBP superalloy using liquid metallurgy process for advanced application

One of the greatest challenges of metallic alloys in numerous applications is due to their structural and habitual failure in service. In an attempt to subdue this failure, Aluminium metal matrix composite was developed with the inclusion of carbonized chicken bone powder (CCBP) as the reinforcing particulate. The addition of the nano-sized CCBP was carried out at different percentage weight on an Al6063 alloy. The production of Aluminium metal matrix composite (A6063-CCBP) was achieved using stir casting comprising 0, 5, 10, and 15 wt per cent of CCBP. The electrochemical and weight loss test conducted in 0.5 M of hydrochloric acid on the composite reveal an improved corrosion resistance. Conventional mechanical tests; hardness and tensile test carried out on the composite using Vickers hardness technique and Universal tensile machine respectively showed that the composite now exhibits better mechanical properties. The comparison of the electrical properties from the electrical test carried out pointed to the fact that incorporation of CCBP into Al6063 provided some level of insulation. Also, the morphological change via SEM (Scanning Electron Microscope) micrograph unveiled that the inclusion of CCBP in the A6063 metal matrix reduced cleavages, showing uniform dispersion of the reinforcement along the grain boundaries and more so, minimised brittle fracture.

Numerical investigation of evolution of earing, anisotropic yield and plastic potentials in cold rolled FCC aluminium alloy based on the crystallographic texture measurements

The mechanical anisotropy of FCC aluminium alloy is influenced by the polycrystalline orientations transformed by cold rolling. The relationship between mechanical anisotropy and evolution of crystallographic textures was established using the crystal plasticity finite element method (CPFEM) based on measured polycrystalline orientation density functions (ODFs) and used to determine the parameters of a phenomenological convex anisotropic yield function which are solved with an implicit finite element (FE) stress integration code. A multi-scale modelling system is generated by combining CPFEM and the phenomenological yield function enabling accurate simulations of forming operations without the need for conventional physical mechanical testing of the material.

High temperature nano-indentation of tungsten: Modelling and experimental validation

It is very well known that tungsten is intrinsically brittle at room temperature, and the characterization of its ductile properties by conventional mechanical tests is possible only above the ductile-to-brittle transition temperature (DBTT), i.e. above 500–700 K. However, the design of tungsten-based components often requires the knowledge of constitutive laws below the DBTT. Here, we carried out instrumented hardness measurements in the temperature range of 300–691 K by nano-indentation. The obtained results are used to extend a set of constitutive laws for the plastic deformation of tungsten, developed earlier on the basis of tensile data, which now covers the temperature range of 300–1273 K. The validation of the constitutive laws was realized by the crystal plasticity finite element method (CPFEM) model, which was applied to simulate the nano-indentation loading curves. The distribution of stress and strain under the indenter was also studied by the CPFEM to bring an insight on the extension of the plastic zone in the process of the indentation, which is of crucial importance when nano-indentation is used to resolve the microstructural features generated by e.g. irradiation by energetic particles, plasma exposure or thermo-mechanical treatment.