Nonhomogeneous Materials Research Articles

Thermal stress analysis of a thermosensitive functionally graded rectangular plate due to thermally induced resultant moments

Purpose The purpose of this paper is to determine the temperature distribution of a thin rectangular plate made of thermosensitive functionally graded (FG) material. By finding out thermal deflection and stress resultants, the thermal stresses have been obtained and analyzed. Design/methodology/approach Initially, the rectangular plate is kept at the surrounding temperature. The upper, lower and two parallel sides (y=0, b and z=0, c) are thermally insulated, while other parallel sides (x=0, a) are given convective-type heating, that is, the rate of change of the temperature of the rectangular plate is proportional to the difference between its own temperature and the surrounding temperature. The non-linear heat conduction equation has been converted to linear form by introducing Kirchhoff’s variable transformation and the resultant heat conduction equation is solved by integral transform technique with hyperbolic varying point heat source. Findings A mathematical model is prepared for FG ceramic–metal-based material, in which alumina is selected as the ceramic and nickel as the metal. The thermal deflection and thermal stresses have been obtained for the homogeneous and nonhomogeneous materials. The results are illustrated numerically and depicted graphically for comparison. During this study, one observed that variations are seen in the stresses, due to the variation in the inhomogeneity parameters. Research limitations/implications The paper is constructed purely on theoretical mathematical modeling by considering various parameters and functions. Practical implications This type of theoretical analysis may be useful in high-temperature environments like nuclear components, spacecraft structural members, thermal barrier coatings, etc., as the effect of temperature and evaluation of temperature-dependent and nonhomogeneous material properties plays a vital role for accurate and reliable structural analysis. Originality/value In this paper, the authors have used thermal deflection and resultant stresses to determine the thermal stresses of a thin rectangular plate with temperature- and spatial variable-dependent material properties which is a new and novel contribution to the field.

Variability on ethyl glucuronide concentrations in hair depending on sample pretreatment, using a new developed GC–MS/MS method

Quantitative determination of ethyl glucuronide in keratin matrix, particularly in hair samples, provides a significant contribution to the evaluation of the extent of ethanol intake. The first-choice method to carry out this analysis is LC–MS/MS, but other techniques may be used. The aim of this work is: a) to develop and validate a GC–MS/MS method for ethyl glucuronide determination in hair; b) to compare GC–MS/MS and LC–MS/MS in analysis of real samples; c) to compare EtG concentration obtained after hair cutting and pulverization.About 30 mg hair samples were washed, pulverized and soaked in 1 ml deionized water. After incubation, the solution was purified through a SPE anion exchange cartridge; the eluate was dried under nitrogen stream, derivatized with PFPA and reconstituted in n-hexane. Then, the sample was injected in the GC–MS/MS system, operating in negative chemical ionization mode and in selected reaction monitoring. The two most intense transitions were used to monitor ethyl glucuronide and deuterated internal standard. All the validation parameters fulfilled the international acceptance criteria. LOD and LOQ were set at 2.0 and 3.0 pg/mg respectively.This method was applied to 194 hair samples collected from teetotallers and alcohol consumers and represents a suitable alternative to LC–MS/MS for the determination of EtG in hair samples, in particular when scarce quantity of hair is available. This study confirmed that pulverization of hair increases the concentration of EtG, but some variability of EtG levels remains probably due to the presence of non-homogeneous material even though pulverization.

Contact problem of a graded layer supported by two rigid punches

This paper considers the frictionless contact plane problem of an infinitely graded layer supported by two rigid cylindrical punches and subjected to a concentrated normal force by means of a rigid cylindrical punch. The layer is made of non-homogeneous material with an isotropic stress–strain law with exponentially varying properties. Rather than assuming vanishing displacements or stresses at the bottom of the geometry, this study examines the effect of supports on the graded layer. Using standard Fourier transform and the related boundary conditions, the plane elasticity equations are converted analytically to a system of singular integral equations in which the unknowns are the contact stresses and areas. Gauss–Chebyshev integration formulas are then employed to discretize and solve numerically the derived integral equations. Numerical results for the contact stresses and areas are provided for various dimensionless quantities including material inhomogeneity, distance between the punches, external load and upper and lower punch radii.

Dynamika zużycia płytek skrawających podczas toczenia niejednorodnego materiału na przykładzie polimerobetonu

The article presents the results of studies on the dynamics of wear of five different cutting inserts (for machining difficult-to-cut materials, for finishing cast iron machining, for roughing cast iron machining, for steel machining and for stainless steel machining) during turning a non-homogeneous material such as polymer concrete. Polymer concrete is a difficult-to-cut, anisotropic, composite material. During the tests, a record of the components of the cutting force in real time was made. After each machining pass, the Ra and Rz surface roughness values were measured in the direction perpendicular to the machining marks and photos were taken under the microscope of the inserts corners, on the basis of which the width of major flank wear land and the width of minor flank wear land were measured. The view of each insert after the tests was also presented. Finally, the conclusions about the dynamics of wear of inserts taking part in the study as well as their applicability during polymer concrete turning were formulated.

Tool wear monitoring in rock drilling applications using vibration signals

Tool wear highly influences the safety, productivity, and overall performance of rock drilling operations. Since rock is a brittle, non-homogeneous, and anisotropic material whose physico-mechanical properties usually vary substantially in the cutting zone, tool wear monitoring could potentially be a very difficult task. Nevertheless, the need for wear monitoring in a fully automated drilling environment is essential. Its function is not only to monitor and diagnose the cutting process but also to provide precise information that enables real-time adjustment of machining parameters. Therefore, a preliminary experimental study of the rock drilling process was performed on limestone and marble in order to determine whether vibration signals can usefully classify the level of drill wear. Accordingly, signals were measured on all three orthogonal axes and tool wear features were extracted from the frequency spectrum in the form of energies related to different bandwidths. Feature extraction and selection was performed using a new proposed methodology. Selected features were finally processed using an artificial neural network classifier. Results confirm the potential usefulness of signal analysis and the proposed methodology to classify tool wear levels during rock drilling.

Transient Dynamic Stress Intensity Factor of FGM Plates Using the State Space and MLPG Methods

In this paper, a new effective method named state-space is extended and utilized to analyze FGM dynamic fracture problems, discretized by the meshless local Petrov–Galerkin method. Both the moving least square and the direct method have been applied to estimate the shape function and to impose the essential boundary conditions. The visibility criterion is used to simulate the displacement and stress field around the crack tip. Normalized dynamic stress intensity factors are calculated using the path-independent integral, J*, which is formulated for the non-homogeneous material. Two methods commonly used in solving such discretized problems, namely, the central difference method and the Newmark method, are compared with the proposed method. Both homogeneous and non-homogeneous (FGM) center-cracked plates under uniform tensile impact load are used to examine the accuracy and the computational time of the new method. The results of the implementation of these methods are compared with existent solutions. The results show that the state-space method saves substantial computational time for a given accuracy. The center-cracked plate made of FGM with two different material gradations (along and normal to the crack length) and four different FGM zones under the effect of uniform tensile impact load are considered, and the dynamic stress intensity factors are studied under the influence of various non-homogeneity ratios.

On Gc, Jc and the characterisation of the mode-I fracture resistance in delamination or adhesive debonding

We focus on the mode-I quasi-static crack propagation in adhesive joints or composite laminates, where inelastic behaviour is due to damage on a relatively thin interface that can be effectively modelled with a cohesive-zone model (CZM). We studied the difference between the critical energy release rate, Gc, introduced in linear elastic fracture mechanics (LEFM), and the work of separation, Ω, i.e. the area under the traction-separation law of the CZM. This difference is given by the derivative, with respect to the crack length, of the energy dissipated ahead of the crack tip per unit of specimen width. For a steady-state crack propagation, in which that energy remains constant as the crack tip advances, this derivative vanishes and Ω=Gc. Thus, the difference between Ω and Gc depends on how far from steady-state the process is, and not on the size of the damage zone, unlike what is stated elsewhere in the literature. Therefore, even for very ductile interfaces, Gc=Ω for a double cantilever beam (DCB) loaded with moments and their difference is extremely small for a DCB loaded with forces. We also show that the proof that the critical value of the J integral, Jc, is equal to the nonlinear energy release rate is not valid for a non-homogeneous material. To compute Gc for a DCB, we use a method based on the introduction of an equivalent crack length, aeq, where the solution is a product of a closed-form part, which does not require the measurement of the actual crack length, and of a corrective factor where the knowledge of the actual crack length is required. However, we also show that this factor is close to unity and therefore has a very small effect on Gc.

Drilling Strategy for Thick Carbon Fiber Reinforced Polymer Composites (CFRP): A Preliminary Assessment

Carbon fiber reinforced polymer or CFRP composites are the epitome of high-performance materials in lightweight design. However, their machinability can be problematic due to non-homogenous and anisotropic material properties. This preliminary assessment emphasizes drilling strategy by using mechanical drilling and laser machining on 25.4 mm thick CFRP, which has not been investigated so far. In mechanical drilling, three drilling strategies were applied with the same parameters in order to assess the feasibility of drilling thick CFRP. The laser machining experiments were conducted to identify the potential of fiber laser machines to cut thick CFRP due to their superior laser beam quality. The results showed that choosing the appropriate drilling strategy in mechanical drilling is essential for reducing damage when drilling thick CFRP. Significant damage occurred in all experiments. The results are useful to define the relationships between machining parameters related to mechanical/laser drilling and hole/cut quality.

Free vibration of fully functionally graded carbon nanotube reinforced graphite/epoxy laminates

This study provides the first-known vibration analysis of fully functionally graded carbon nanotube reinforced hybrid composite (FFG-CNTRHC) laminates. CNTs are non-uniformly distributed to reinforce the graphite/epoxy laminates. Some CNT distribution functions in the plane and thickness directions are proposed to more efficiently increase the stiffening effect. The rule of mixtures is modified by considering the non-homogeneous material properties of FFG-CNTRHC laminates. The formulation of the location dependent stiffness matrix and mass matrix is derived. The effects of CNT volume fraction and distribution on the natural frequencies of FFG-CNTRHC laminates are discussed. The results reveal that the FFG layout may significantly increase the natural frequencies of FFG-CNTRHC laminate.

Robust non-destructive measurement system for extraction of ultrasonic wave parameters using the prism technique

Abstract In this paper we propose a measurement system to evaluate the elastic constants of materials using only one experiment. This measurement system is based on the ultrasonic prism technique for the nondestructive measurement of both compressional and shear waves, and on the matching pursuit combined with genetic algorithms (MP-GA) to estimate these two backscattered echo waves. Under this framework, samples are realized in prism-shaped forms using a special molding box. Then, the MP-GA method is used to derive the time of flight of the measured data by a deconvolution process. The backscattered echoes are constructed using a parametric model-based vector for which the corresponding parameters are closely related to the physical properties of the ultrasonic signal propagating through the investigated material. The effectiveness of the measurement system is approved by estimating the elastic properties of homogeneous and non-homogeneous solid materials. Further, several tests have shown that this measurement system works well even for low SNR levels.

Dominance of debonding defect of CFST on PZT sensor response considering the meso-scale structure of concrete with multi-scale simulation

Abstract Piezoelectric-lead-zirconate-titanate(PZT)-based interface debonding defects detection for concrete filled steel tubulars (CFSTs) has been proposed and validated through experiments, and numerical study on its mechanism has been carried out recently by assuming that concrete material is homogenous. However, concrete is composed of coarse and fine aggregates, mortar and interface transition zones (ITZs) and even initial defects and is a typical nonhomogeneous material and its mesoscale structure might affect the wave propagation in the concrete core of CFST members. Therefore, it is significantly important to further investigate the influence of mesoscale structure of concrete on the stress wave propagation and the response of embedded PZT sensor for the interface debonding detection. In this study, multi-physical numerical simulation on the wave propagation and embedded PZT sensor response of rectangular CFST members with numerical concrete core considering the randomness in circular aggregate distribution, and coupled with surface-mounted PZT actuator and embedded PZT sensor is carried out. The effect of randomness in the circular aggregates distribution and the existence of ITZs are discussed. Both a local stress wave propagation behavior including transmission, reflection, and diffraction at the interface between concrete core and steel tube under a pulse signal excitation and a global wave field in the cross-section of the rectangular CFST models without and with interface debonding defects under sweep frequency excitation are simulated. The sensitivity of an evaluation index based on wavelet packet analysis on the embedded PZT sensor response on the variation of mesoscale parameters of concrete core without and with different interface debonding defects under sweep frequency voltage signal is investigated in details. The results show that the effect of the interface debondings on the embedded PZT measurement is dominant when compared to the meso-scale structures of concrete core. This study verified the feasibility of the PZT based debonding detection for rectangular CFST members even the meso-scale structure of concrete core is considered.

Optimization of crane setup location and servicing schedule for urgent material requests with non-homogeneous and non-fixed material supply

Abstract Reducing hook movement distances could decrease crane operation times to deliver heavyweight materials in construction sites. Conventional scheduling methods include first-in-first-serve (FIFS), shortest-job-first (SJF), nearest-neighbor-first (NNF), and Traveling salesman problem (TSP). A new optimization model to optimize crane setup location, hook movement sequences and servicing schedules serving all supply and demand locations is proposed. Proposed model is able to model homogeneous and non-homogeneous material supply. Initial hook location can be given as input for optimization. Fixed material supply and demand location pairs are relaxed as model variables. Maximum crane lifting capacity is considered and multiple hook movement trips between material supply and demand locations are modeled if requested material weights exceed this maximum crane lifting capacity. Users may place “urgent” material demand requests and the proposed optimization model can optimize a servicing sequence to prioritize all urgent requests. The problem is formulated as a Binary-Mixed-Integer-Linear-Program (BMILP) which is solved by standard branch-and-bound techniques. Significant reduction in total operation time is achieved while comparing to other conventional scheduling strategies.

Effects of Cyclic Loading on the Mechanical Properties of Mature Bedding Shale

We investigated the mechanical properties of mature bedding shale under cyclic loading conditions, with an application to the design of hydraulic fracturing in shale gas wells. Laboratory experiments were conducted on shale samples under two principal loading orientations. Testing results showed that accumulated fatigue damage occurs in a three‐stage process. Analysis of fatigue damage at different maximum stress levels shows that fatigue life increases as a power‐law function with maximum stress decreasing. And the maximum stress significantly affects the fatigue life. Further, the elastic part of shale rock deformation was recovered in the unloading process, whereas the irreversible deformation remained. The irreversible deformation, growth trend, and accumulation of the total fatigue were directly related to the fatigue damage. This process can be divided into 3 stages: an initial damage stage, a constant velocity damage stage, and an accelerated damage stage, which accounted for about one‐third of the fatigue damage. Shale rock is a nonhomogeneous material, and the bedding is well developed. Its fatigue life differs greatly in two principal loading orientations, even under the same loading conditions. All of these drawn conclusions are of great importance for design of hydraulic fracturing in shale gas wells.

РАЗРУШАЮЩИЕ ТЕРМОУПРУГИЕ НАПРЯЖЕНИЯ ИЗ-ЗА ТЕПЛОВЫДЕЛЕНИЯ В ГАЗОВЫХ ВКЛЮЧЕНИЯХ В КОМПОЗИЦИОННЫХ МАТЕРИАЛАХ

The paper considers such important phenomenon in radio components as the cleavage in multicomponent materials. Composite materials are the important class of radio materials, thus the improvement of complex of their properties has the important fundamental and applied significance and is the up-to-date sector of the material science. The improvement of composite materials contributes to their wider application and production of new radio components. Alongside with the composite materials properties’ improvement, the compounds where other elements, for example, rare-earth (alloys with praseodymium or samarium) are applied are of considerable interest. The paper studies the influence of thermoelastic stresses on the performance capacity of radio components containing composite materials, identifies physical factors influencing most greatly the operational suitability of the products with the composite materials. The author had an objective to study the mechanisms of initiation and behavior of a thermoelastic breakdown in a composite material containing the inclusions, in particular, air inclusions. For example, metal-based composite material contains dozens of inclusions of various compositions. As a rule, composite materials contain air inclusions the influence of which should be taken into account as well. The electrical strength and the service life of the details produced from the non-homogeneous composite materials within the strong electric fields depend on the content of air inclusions and their shape. The paper presents the calculation of the electric field strength in the inclusions and near them. The author considered the process taking place in an ellipsoidal inclusion under the influence of strong electric field and analyzed the relative influence of large inclusions’ shape on the hardening mechanism. The processes for small and large inclusions in a composite material and their influence on the destruction of the details caused by the discharges in the inclusions are considered separately. The influence of complex external action (different temperatures, etc.) is studied. It is identified that the heat generation caused in the strong high-frequency fields by the ionization in air inclusions in composite materials can be significant and, under the strong external actions, the destructive stresses can occur. The uneven heating of a composite material leads to the appearance of destructive thermoelastic stresses and to the cleavage of radio components caused by the heat generation in large inclusions.

Finite element analysis of fretting contact for nonhomogenous materials

Fretting problem arises in the case of relatively small sliding motion between contacting surfaces. Fatigue life of the components that are in contact with each other, especially in rotorcraft may be significantly reduced due to fretting. The purpose of this study is to investigate material inhomogeneity near the contact region on the fretting problem in a cylindrical on flat contact configuration. A finite element (FE) model was constructed by using commercial finite element package ABAQUSTMto study partial sliding and stress concentrations. In order to investigate the effect of material inhomogeneity, the fretting contact is analyzed by introducing voids near the contact region. The void size and an array of voids is introduced into the substrate. The results are compared in terms of pressure, shear traction, tangential stress magnitudes and relative slip between the contacting materials.

Study on the side milling properties of metal - composite co-cured materials

Satellite attitude control flywheel is the important component of the attitude control system in military light agile satellite. At present, a main trend has arisen with using high performance composite material to satisfy the lightweight, large moment and long life of the attitude control flywheel. However, defects such as delamination, splitting, resin burn, and subsurface damage may be likely to occur during the cutting process owing to the anisotropic and non-homogeneous material structure of CFRP. In this paper, the single factor milling experiment was conducted. Invar-M30 composite co-curing materials were milled with different cutting speeds and feeds. The milling force and surface integrity, including the surface topography, defects and the bonding condition of the machined surface, were emphatically tested and analyzed to further study surface defects and its causes, and research the main factors affecting the quality of the processing surface. Finally, based on the cutting force and surface integrity detected on the experiment, the cutting parameters of the Invar-M30 composite co-cured material were optimized, which may supply experimental support for the manufacture of the attitude control flywheel.

A numerical method for the thermal-shock crack problems of nonhomogeneous materials with inclusions based on an interaction energy integral method

Nonhomogeneous materials, especially for particulate composites, usually contain defects such as voids and debonding introduced during manufacturing process. Due to existence of defects, nonhomogeneous materials are prone to fracture failure under thermal shock loading. This paper aims to develop a set of methods for analysing the thermal-shock crack problems of nonhomogeneous material plates (NMPs) with inclusions. A modified domain-independent interaction energy integral method (IEIM) is developed to obtain the mixed-mode transient thermal stress intensity factors (TSIFs). Then the IEIM, the extended finite element method (XFEM) and the finite difference method (FDM) are combined together to address a thermal-shock crack problem of a NMP with an inclusion. With the methods, the influences of the inclusion on the transient mixed-mode TSIFs are investigated. The results show that the present method can be applied to solve the thermal shock crack problem effectively. Furthermore, the relations between the mixed-mode TSIFs and model parameters including material constants as well as locations of the inclusion are established. It is found that the thermal expansion coefficient and Young’s modulus of the inclusion affect the mixed-mode TSIFs in a dominant manner in comparison with other factors such as the specific heat, heat conductivity and density of the inclusion affect the TSIFs slightly. Specifically, the critical normalized distance, beyond which the influence of the inclusion on the mixed-mode TSIFs is negligible, is revealed. The present work will be significant for fracture mechanics analysis and design of nonhomogeneous materials with inclusions.

Auxetics and Other Systems of Anomalous Characteristics

Auxetics and Other Systems of Anomalous Characteristics

A mesh-free Monte-Carlo method for simulation of three-dimensional transient heat conduction in a composite layered material with temperature dependent thermal properties

A new solution for the three-dimensional transient heat conduction from a homogeneous medium to a non-homogeneous multi-layered composite material with temperature dependent thermal properties using a mesh-free Monte-Carlo method is proposed. The novel contributions include a new algorithm to account for the impact of thermal diffusivities from source to sink in the calculation of the particles’ step length (particles are represented as bundles of energy emitted from each source), and a derivation of the three-dimensional peripheral integration to account for the influence of material properties around the sink on its temperature. Simulations developed using the proposed method are compared against both experimental measurements and results from a finite element simulation.

On the impossibility of arbitrary deformations in nonlinear elasticity

We employ partly Sobolev classes to obtain a necessary condition for mappings of $$W^{1,p}$$ -class to be deformations of nonlinearly elastic bodies that can be induced by $$L^{q}$$ -forces, $$1\le p,\,q <\infty $$ . This condition is useful for studying continuous deformations of non-homogeneous materials and for obtaining stable numerical methods for nonlinear elasticity.