Stiffness Evaluation for Solids Containing Dilute Distributions of Inclusions and Microcracks

1995 ◽  
Vol 62 (1) ◽  
pp. 71-77 ◽  
Author(s):  
Y. Huang ◽  
K. X. Hu ◽  
A. Chandra
Keyword(s):  
Crack Opening ◽  
Matrix Material ◽  
Numerical Approach ◽  
Stiffness Evaluation ◽  
Growing Crack ◽  
Crack Interactions ◽  
The Matrix ◽  
Additional Strain ◽  
Self Similar ◽  
Nonuniform Stress Field

Materials, such as ceramics, intermetallics, and rocks, contain varying amounts of inhomogeneities, and the matrix material is vulnerable to microcracking in the neighborhood around these inhomogeneities. In an attempt to model the micromechanical aspects of this type of material, a solid containing dilute inclusions surrounded by cracks is investigated in this paper. The dilute-inclusion assumption neglects any interactions among different inclusion-crack clusters, but local inclusion-crack and crack-crack interactions are taken into account fully. It is shown that additional strain due to microcracking in a solid containing inclusions can be represented by an integral of crack opening displacements weighted by a nonuniform stress field induced by inclusions alone (in the absence of microcracking). An effective numerical approach is then developed to evaluate the effective moduli and additional macroscopic strain due to microcracking in composites. It is found that an increase in the number of hard inclusions may not always lead to expected strengthening of the materials, if the matrix material is vulnerable to microcracking around inclusions and a relatively large microcracking zone develops. The limited calculations show that a quasi-static crack-growing process can lead to an actively growing crack being arrested or to a stationary crack starting to grow. This suggests that self-similar crack growth may not be enough to describe the behavior of microcracked composites.

scholarly journals Notch (In)Sensitivity of Aluminum Matrix Syntactic Foams

Materials ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 574 ◽  
Author(s):  
Attila Szlancsik ◽  
Bálint Katona ◽  
Dóra Károly ◽  
Imre Orbulov
Keyword(s):  
Fracture Toughness ◽  
Crack Opening ◽  
Matrix Material ◽  
Hollow Spheres ◽  
Aluminum Matrix ◽  
Syntactic Foams ◽  
Complex Investigation ◽  
Pressure Infiltration ◽  
Three Point Bending ◽  
The Matrix

Aluminum alloy (Al99.5 or AlSi12)-based metal matrix syntactic foams (MMSFs) were produced by pressure infiltration with ~65 vol % Globocer filler (33 wt % Al2O3, 48 wt % SiO2, 19 wt % Al2O3∙SiO2). The infiltrated blocks were machined by different geometry tools in order to produce notched samples. The samples were loaded in three-point bending, and the loading force values were recorded against the cross-head displacements and the crack opening displacements. To measure up the notch sensitivity and toughness of the MMSFs, the fracture energies and the fracture toughness values were determined. The results showed that the mentioned quantities are needed to describe the behavior of MMSFs. The fracture energies were shown to be notch-sensitive, while the fracture toughness values were dependent only on the matrix material and were insensitive to the notch geometry. The complex investigation of the fracture surfaces revealed strong bonding between the hollow spheres and the Al99.5 matrix due to a chemical reaction, while this bonding was found to be weaker in the case of the AlSi12 matrix. This difference resulted in completely different crack propagation modes in the case of the different matrices.

Polishing process effect on the image of dispersed precipitates

1984 ◽  
Vol 42 ◽  
pp. 534-535
Author(s):  
C.T. Hu ◽  
C.W. Allen
Keyword(s):  
Matrix Material ◽  
Specimen Preparation ◽  
Second Phase ◽  
Precipitate Particle ◽  
Polishing Process ◽  
Second Phase Particles ◽  
The Matrix ◽  
Surface Profiles ◽  
Thinning Process

One important problem in determination of precipitate particle size is the effect of preferential thinning during TEM specimen preparation. Figure 1a schematically represents the original polydispersed Ni3Al precipitates in the Ni rich matrix. The three possible type surface profiles of TEM specimens, which result after electrolytic thinning process are illustrated in Figure 1b. c. & d. These various surface profiles could be produced by using different polishing electrolytes and conditions (i.e. temperature and electric current). The matrix-preferential-etching process causes the matrix material to be attacked much more rapidly than the second phase particles. Figure 1b indicated the result. The nonpreferential and precipitate-preferential-etching results are shown in Figures 1c and 1d respectively.

Application of cross correlation to HREM images of surfaces

1987 ◽  
Vol 45 ◽  
pp. 754-755
Author(s):  
D. E. Luzzi ◽  
L. D. Marks ◽  
M. I. Buckett
Keyword(s):  
Cross Correlation ◽  
A Priori ◽  
Matrix Material ◽  
Correlation Method ◽  
Accurate Knowledge ◽  
Complex Image ◽  
Fourier Filtering ◽  
The Matrix ◽  
Low Pass ◽  
Data Reduction Technique

As the HREM becomes increasingly used for the study of dynamic localized phenomena, the development of techniques to recover the desired information from a real image is important. Often, the important features are not strongly scattering in comparison to the matrix material in addition to being masked by statistical and amorphous noise. The desired information will usually involve the accurate knowledge of the position and intensity of the contrast. In order to decipher the desired information from a complex image, cross-correlation (xcf) techniques can be utilized. Unlike other image processing methods which rely on data massaging (e.g. high/low pass filtering or Fourier filtering), the cross-correlation method is a rigorous data reduction technique with no a priori assumptions.We have examined basic cross-correlation procedures using images of discrete gaussian peaks and have developed an iterative procedure to greatly enhance the capabilities of these techniques when the contrast from the peaks overlap.

Impact Strength, Flexural Modulus and Wear Rate of PMMA Composites Reinforced by Eggshell Powders

2020 ◽  
Vol 38 (7A) ◽  
pp. 960-966
Author(s):  
Aseel M. Abdullah ◽  
Hussein Jaber ◽  
Hanaa A. Al-Kaisy
Keyword(s):  
Impact Strength ◽  
Wear Rate ◽  
Flexural Modulus ◽  
Matrix Material ◽  
Weight Fraction ◽  
Pure Pmma ◽  
Calcination Process ◽  
The Matrix ◽  
The Impact ◽  
Interface Bond

In the present study, the impact strength, flexural modulus, and wear rate of poly methyl methacrylate (PMMA) with eggshell powder (ESP) composites have been investigated. The PMMA used as a matrix material reinforced with ESP at two different states (including untreated eggshell powder (UTESP) and treated eggshell powder (TESP)). Both UTESP and TESP were mixed with PMMA at different weight fractions ranged from (1-5) wt.%. The results revealed that the mechanical properties of the PMMA/ESP composites were enhanced steadily with increasing eggshell contents. The samples with 5 wt.% of UTESP and TESP additions give the maximum values of impact strength, about twice the value of the pure PMMA sample. The calcination process of eggshells powders gives better properties of the PMMA samples compared with the UTESP at the same weight fraction due to improvements in the interface bond between the matrix and particles. The wear characteristics of the PMMA composites decrease by about 57% with increases the weight fraction of TESP up to 5 wt.%. The flexural modulus values are slightly enhanced by increasing of the ESP contents in the PMMA composites.

scholarly journals Self-Reinforced Nylon 6 Composite for Smart Vibration Damping

Polymers ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1235
Author(s):  
Bidita Salahuddin ◽  
Rahim Mutlu ◽  
Tajwar A. Baigh ◽  
Mohammed N. Alghamdi ◽  
Shazed Aziz
Keyword(s):  
Matrix Material ◽  
Nylon 6 ◽  
Vibration Damping ◽  
Vibration Energy ◽  
Damping Factor ◽  
Passive Vibration Control ◽  
Reinforced Composite ◽  
Coiled Structure ◽  
The Matrix ◽  
3D Printed

Passive vibration control using polymer composites has been extensively investigated by the engineering community. In this paper, a new kind of vibration dampening polymer composite was developed where oriented nylon 6 fibres were used as the reinforcement, and 3D printed unoriented nylon 6 was used as the matrix material. The shape of the reinforcing fibres was modified to a coiled structure which transformed the fibres into a smart thermoresponsive actuator. This novel self-reinforced composite was of high mechanical robustness and its efficacy was demonstrated as an active dampening system for oscillatory vibration of a heated vibrating system. The blocking force generated within the reinforcing coiled actuator was responsible for dissipating vibration energy and increase the magnitude of the damping factor compared to samples made of non-reinforced nylon 6. Further study shows that the appropriate annealing of coiled actuators provides an enhanced dampening capability to the composite structure. The extent of crystallinity of the reinforcing actuators is found to directly influence the vibration dampening capacity.

Investigation on the Influence of Pressure Terms in a Volume-Averaged Energy Balance in the Modelling of Liquid Composite Moulding Processes

2019 ◽  
Vol 809 ◽  
pp. 480-486
Author(s):  
Rohit George Sebastian ◽  
Christof Obertscheider ◽  
Ewald Fauster ◽  
Ralf Schledjewski
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Energy Balance ◽  
Matrix Material ◽  
Energy Balance Equation ◽  
Manufacturing Processes ◽  
Composite Manufacturing ◽  
Liquid Composite Moulding ◽  
The Matrix ◽  
Computational Fluid Dynamics Cfd

The growing use of composite materials has generated interest in improving and optimising composite manufacturing processes such as Liquid Composite Moulding (LCM). In LCM, dry preforms are placed in a mould and impregnated with the matrix material. The efficiency of filling the moulds can be improved by using Computational Fluid Dynamics (CFD) filling simulations during the design of the mould. As part of an on-going effort to develop a CFD tool for the simulation of LCM processes, a volume averaged energy balance equation has been derived and implemented in a custom OpenFOAM solver. The energy balance is implemented in a custom OpenFOAM solver with and without the pressure terms for comparison with results from RTM experiments. It is found that the pressure terms do not significantly influence the results for LCM processes.

Stochastic Aspects of Matrix Cracking in Brittle Matrix Composites

1993 ◽  
Vol 115 (3) ◽  
pp. 314-318 ◽  
Author(s):  
S. M. Spearing ◽  
F. W. Zok
Keyword(s):  
Matrix Cracking ◽  
Matrix Composites ◽  
Brittle Matrix ◽  
Tensile Response ◽  
Brittle Matrix Composites ◽  
Crack Interactions ◽  
The Matrix ◽  
Interface Slip ◽  
Bridging Fibers

A computer simulation of multiple cracking in fiber-reinforced brittle matrix composites has been conducted, with emphasis on the role of the matrix flaw distribution. The simulations incorporate the effect of bridging fibers on the stress required for cracking. Both short and long (steady-state) flaws are considered. Furthermore, the effects of crack interactions (through the overlap of interface slip lengths) are incorporated. The influence of the crack distribution on the tensile response of such composites is also examined.

scholarly journals A Numerical Approach for Evaluating the Time-Dependent Distribution of a Quasi Birth-Death Process

2021 ◽  
Author(s):  
Michel Mandjes ◽  
Birgit Sollie
Keyword(s):  
Continuous Time ◽  
Real Life ◽  
Numerical Approach ◽  
Time Dependent ◽  
Death Process ◽  
Continuous Time Markov Chain ◽  
Likelihood Estimator ◽  
Real Life Data ◽  
The Matrix ◽  
Birth Death

AbstractThis paper considers a continuous-time quasi birth-death (qbd) process, which informally can be seen as a birth-death process of which the parameters are modulated by an external continuous-time Markov chain. The aim is to numerically approximate the time-dependent distribution of the resulting bivariate Markov process in an accurate and efficient way. An approach based on the Erlangization principle is proposed and formally justified. Its performance is investigated and compared with two existing approaches: one based on numerical evaluation of the matrix exponential underlying the qbd process, and one based on the uniformization technique. It is shown that in many settings the approach based on Erlangization is faster than the other approaches, while still being highly accurate. In the last part of the paper, we demonstrate the use of the developed technique in the context of the evaluation of the likelihood pertaining to a time series, which can then be optimized over its parameters to obtain the maximum likelihood estimator. More specifically, through a series of examples with simulated and real-life data, we show how it can be deployed in model selection problems that involve the choice between a qbd and its non-modulated counterpart.

Localized Necking in a Round Tensile Bar with HCP Material Considering Tension-Compression Asymmetry in Plastic Flow

2013 ◽  
Vol 535-536 ◽  
pp. 164-167
Author(s):  
Jonghun Yoon ◽  
Oana Cazacu ◽  
Jung Hwan Lee
Keyword(s):  
Yield Criterion ◽  
Matrix Material ◽  
Ductile Failure ◽  
Material Behavior ◽  
Strength Differential ◽  
The Matrix ◽  
Void Evolution ◽  
Hcp Materials ◽  
Spherical Voids ◽  
Tension Compression Asymmetry

In spite of this progress in predicting ductile failure, the development of macroscopic yield criteria for describing damage evolution in HCP (hexagonal close-packed) materials remains a challenge. HCP materials display strength differential effects (i.e., different behavior in tension versus compression) in the plastic response due to twinning. Cazacu and Stewart [1] developed an analytic yield criterion for a porous material containing randomly distributed spherical voids in an isotropic, incompressible matrix that displays tension-compression asymmetry. The matrix material was taken to obey the isotropic form of the Cazacu et al. [2] yield criterion, which captures the tension-compression asymmetry of the matrix material. In this paper, finite element calculations of a round tensile bar are conducted with the material behavior described by the Cazacu and Stewart [1] yield criterion. The goal of these calculations is to investigate the effect of the tension-compression asymmetry on the necking induced by void evolution and propagation.

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