A Computational Study of Interfacial Stress Distribution in Unidirectional Composites and Its Use in Prediction of Brittle Failure

Aerospace ◽  
2003 ◽  
Author(s):  
Xiaoming Chen ◽  
Thanasis D. Papathanasiou
Keyword(s):  
Brittle Failure ◽  
Composite Structures ◽  
Computational Study ◽  
Tensile Load ◽  
Interfacial Stress ◽  
Uniaxial Tensile ◽  
Unidirectional Composites ◽  
Material Parameters ◽  
Specific Shape ◽  
Random Composite

A computational investigation has been conducted to examine the effect of key microstructural and material parameters, namely the minimum inter-fiber spacing (δ) and the fiber/matrix stiffness ratio (Ef/Em), on the interfacial stress distributions in unidirectional composites subjected to transverse uniaxial tensile load. Representative Volume Elements (RVE’s) containing 144 fibers are constructed using a Monte-Carlo (MC) algorithm, imitating random composite structures. The boundary element method is then used to solve the multi-region elasticity problem on these microstructures. We pay particular attention to the statistics of the distribution of the maximum interfacial stresses computed on each fiber; these are found to follow a Weibull distribution, whose specific shape depends on both microstructural and material parameters. Following the weakest-link theory of Batdorf and Crose [1], we derive a statistical formula for the prediction of brittle failure of composite structures caused by interfacial failure. The limitations and possible extensions to the proposed approach are discussed as well.

scholarly journals Effect of Defects on Progressive Failure Behavior of Plain Weave Textile Composites

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4363
Author(s):  
Kyeongsik Woo ◽  
Jae Hyuk Lim ◽  
Cheolheui Han
Keyword(s):  
Failure Mode ◽  
Composite Structures ◽  
Progressive Failure ◽  
Tensile Load ◽  
Textile Composites ◽  
Unit Cell ◽  
Structural Safety ◽  
Uniaxial Tensile ◽  
Failure Behavior ◽  
Plain Weave

Various types of internal defects occur during manufacturing and handling of composite materials. It is practically impossible to manufacture composite structures without defects, making it crucial to understand the effect of defects on their failure behavior to maintain structural safety. In this work, the effect of pre-defects on the failure behavior of plain weave textile composites was studied. Unit cell configurations with symmetric, in-phase, and shifted fiber tow arrangements were considered. Inter-laced warp and fill tows and matrix pockets of plain weave unit cells were modeled in three-dimensional finite elements, and cohesive elements were inserted between all bulk elements to account for the fracture modes of the fiber and matrix direction failure of warp and fill tows, matrix pocket failure, and interface failure. Unit cell models containing pre-defects of voids, tow-matrix pocket separation, warp-fill tow separation, and cracks in the warp and fill tows were analyzed, and their effects on progressive failure behavior were investigated in terms of the interaction between fiber tow arrangements and defects. Results indicated that initial failure occurred in matrix-direction failure mode in fill tows, whereas fiber tow-matrix pocket separation was the major failure mode under uniaxial tensile load. Furthermore, failure behavior was found to be highly dependent on the fiber tow arrangement pattern and the location of pre-defects.

Influence of grain direction on the time-dependent behavior of wood analyzed by a 3D rheological model. A mathematical consideration

Holzforschung ◽  
2018 ◽  
Vol 72 (10) ◽  
pp. 889-897 ◽  
Author(s):  
Sabina Huč ◽  
Staffan Svensson
Keyword(s):  
Rheological Model ◽  
Tensile Load ◽  
Longitudinal Direction ◽  
Material Behavior ◽  
Time Dependent ◽  
Sustained Load ◽  
Uniaxial Tensile ◽  
Material Parameters ◽  
Dependent Behavior ◽  
Natural Time

AbstractA three-dimensional (3D) rheological model for an orthotropic material subjected to sustained load or deformation under constant climate has been mathematically formulated. The elastic and viscoelastic compliance matrices are symmetric, where the mathematical derivation of the latter is shown. The model is linear and requires constant numerical values for the elastic and viscoelastic material parameters. The model’s ability to predict the natural time-dependent response in three material directions simultaneously is demonstrated on a Douglas fir (Pseudotsuga menziesii) specimen subjected to a constant uniaxial tensile load. The material extends in a longitudinal direction and contracts in the transverse directions with time. The required material parameters are taken from the literature when possible, otherwise they are assumed. Furthermore, the influence of misalignment between the directions of observation and wood material directions on induced time-dependent strains is analyzed. The analyses show that the misalignment has a large effect on the material behavior. In some cases, the specimen under constant uniaxial tension even extends in the perpendicular transverse direction with time. The obtained results clearly demonstrate the high importance of considering the alignment of material directions precisely in order to be able to interpret the time-dependent behavior of wood correctly.

scholarly journals Numerical Analysis of the Perforated Steel Sheets Under Uni-Axial Tensile Force

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 632 ◽  
Author(s):  
Ahmed M. Sayed
Keyword(s):  
Load Capacity ◽  
Tensile Force ◽  
Three Dimensional ◽  
Tensile Load ◽  
Experimental Tests ◽  
Strain Engineering ◽  
Uniaxial Tensile ◽  
Fe Model ◽  
Stress Strain ◽  
Steel Sheets

The perforated steel sheets have many uses, so they should be studied under the influence of the uniaxial tensile load. The presence of these holes in the steel sheets certainly affects the mechanical properties. This paper aims at studying the behavior of the stress-strain engineering relationships of the perforated steel sheets. To achieve this, the three-dimensional finite element (FE) model is mainly designed to investigate the effect of this condition. Experimental tests were carried out on solid specimens to be used in the test of model accuracy of the FE simulation. Simulation testing shows that the FE modeling revealed the ability to calculate the stress-strain engineering relationships of perforated steel sheets. It can be concluded that the effect of a perforated rhombus shape is greater than the others, and perforated square shape has no effect on the stress-strain engineering relationships. The efficiency of the perforated staggered or linearly distribution shapes with the actual net area on the applied loads has the opposite effect, as it reduces the load capacity for all types of perforated shapes. Despite the decrease in load capacity, it improves the properties of the steel sheets.

scholarly journals Investigating the Effect of Interface Morphology in Adhesively Bonded Composite Wavy-Lap Joints

2021 ◽  
Vol 5 (1) ◽  
pp. 32
Author(s):  
Roya Akrami ◽  
Shahwaiz Anjum ◽  
Sakineh Fotouhi ◽  
Joel Boaretto ◽  
Felipe Vannucchi de Camargo ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Composite Structures ◽  
Failure Modes ◽  
Mechanical Performance ◽  
Tensile Load ◽  
Lap Joints ◽  
Load Level ◽  
Displacement Curve ◽  
Interface Morphology ◽  
Angle Variation

Joints and interfaces are one of the key aspects of the design and production of composite structures. This paper investigates the effect of adhesive–adherend interface morphology on the mechanical behavior of wavy-lap joints with the aim to improve the mechanical performance. Intentional deviation from a flat joint plane was introduced in different bond angles (0°, 60°, 90° and 120°) and the joints were subjected to a quasi-static tensile load. Comparisons were made regarding the mechanical behavior of the conventional flat joint and the wavy joints. The visible failure modes that occurred within each of the joint configurations was also highlighted and explained. Load vs. displacement graphs were produced and compared, as well as the failure modes discussed both visually and qualitatively. It was observed that distinct interface morphologies result in variation in the load–displacement curve and damage types. The wavy-lap joints experience a considerably higher displacement due to the additional bending in the joint area, and the initial damage starts occurring at a higher displacement. However, the load level had its maximum value for the single-lap joints. Our findings provide insight for the development of different interface morphology angle variation to optimize the joints behavior, which is widely observed in some biological systems to improve their performance.

Nondestructive Photoelastic and Machine Learning Characterization of Surface Cracks and Prediction of Weibull Parameters for Photovoltaic Silicon Wafers

2021 ◽  
pp. 1-40
Author(s):  
Logan Rowe ◽  
Alexander J. Kaczkowski ◽  
Tung-Wei Lin ◽  
Gavin Horn ◽  
Harley Johnson
Keyword(s):  
Machine Learning ◽  
Learning Algorithm ◽  
Tensile Load ◽  
Silicon Wafers ◽  
Uniaxial Tensile ◽  
Support Vector ◽  
Weibull Parameters ◽  
Bulk Stress ◽  
Wire Motion

Abstract A nondestructive photoelastic method is presented for characterizing surface microcracks in monocrystalline silicon wafers, calculating the strength of the wafers, and predicting Weibull parameters under various loading conditions. Defects are first classified from through thickness infrared photoelastic images using a support vector machine learning algorithm. Characteristic wafer strength is shown to vary with the angle of applied uniaxial tensile load, showing greater strength when loaded perpendicular to the direction of wire motion than when loaded along the direction of wire motion. Observed variations in characteristic strength and Weibull shape modulus with applied tensile loading direction stem from the distribution of crack orientations and the bulk stress field acting on the microcracks. Using this method it is possible to improve manufacturing processes for silicon wafers by rapidly, accurately, and nondestructively characterizing large batches in an automated way.

Prediction Model of Deflections in PET Fiber Reinforced Concrete Beams

2014 ◽  
Vol 1611 ◽  
pp. 1-6
Author(s):  
F. J. Baldenebro-Lopez ◽  
J. H. Castorena-Gonzalez ◽  
J. A. Baldenebro-Lopez ◽  
J.I. Velazquez-Dimas ◽  
J. E. Ledezma-Sillas ◽  
...  
Keyword(s):  
Reinforced Concrete ◽  
Design Theory ◽  
Load Capacity ◽  
Tensile Load ◽  
Fiber Reinforced Concrete ◽  
Reinforced Concrete Beams ◽  
Flexural Behavior ◽  
Engineering Properties ◽  
Uniaxial Tensile ◽  
Strain Diagram

ABSTRACTThe increasing use of polymeric reinforcements in concrete structures requires either the development of a new design theory or the adaptation of current designs considering the engineering properties of this type of materials. In this work a method for calculating the deflections of reinforced concrete elements is proposed, which can be used in predicting the flexural behavior of longitudinally reinforced concrete with PET strips in amounts up to 1%. The model theory assumes that concrete has a tensile load capacity different to zero, characterized by a uniaxial tensile stress-strain diagram. A series of tests were conducted to corroborate the validity of the suggested method, showing that the theory also correctly predicts the creep deformation post-cracking. The deflection results of reinforced concrete with recycled PET strips are presented. The tests are carried out by a simple beam with center-point loading, using three different amounts of reinforcement and comparing the experimental results with the theoretical results of the proposed model.

Influence of service ageing on polyester-reinforced polyvinyl chloride-coated fabrics reported through mathematical material models

2018 ◽  
Vol 89 (8) ◽  
pp. 1472-1487
Author(s):  
Krzysztof Zerdzicki ◽  
Pawel Klosowski ◽  
Krzysztof Woznica
Keyword(s):  
Polyvinyl Chloride ◽  
Constitutive Models ◽  
Uniaxial Tensile ◽  
Creep Tests ◽  
Material Models ◽  
Material Parameters ◽  
Coated Fabric ◽  
Coated Fabrics ◽  
Term Creep

In this paper the coupled service (constructional tension) and environmental (sunlight, rainfalls, temperature variations) ageing influence on the polyester-reinforced polyvinyl chloride (PVC)-coated fabric VALMEX is studied. Two cases of the same fabric have been analyzed: one USED for 20 years on the real construction of the Forest Opera in Sopot (Poland), and one kept as a spare material (NOT USED). The following tests have been conducted: uniaxial tensile, biaxial tensile and long-term creep tests. The obtained results have been used for the parameter identification of the piecewise non-linear, Burgers and Bodner–Partom models. Next, the analysis of the influence of environmental conditions on the parameters of these models has been made. It has been concluded that some parameters are more and the others are less sensitive to the exposure to environmental and mechanical conditions. The change of material parameters for fill threads (due to larger deformation) is higher. The obtained results may be useful in the durability evaluation of the textile membranes reinforced with polyester threads and PVC coated. All the constitutive models with the identified parameters may be used for the numerical analysis of structures made of fabrics at the service beginning and after long-term usage.

A study on determination of tensile properties of metals at elevated temperatures from spherical indentation tests

2019 ◽  
Vol 54 (5-6) ◽  
pp. 331-347
Author(s):  
Tairui Zhang ◽  
Shang Wang ◽  
Weiqiang Wang
Keyword(s):  
Tensile Properties ◽  
Analytical Model ◽  
Elevated Temperatures ◽  
Regression Function ◽  
Maximum Error ◽  
Analytical Models ◽  
Uniaxial Tensile ◽  
Spherical Indentation ◽  
Material Parameters ◽  
Indentation Tests

In this study, spherical indentation tests were used to determine the uniaxial tensile properties of metals at elevated temperatures (200 °C, 400 °C, and 600 °C). Taking the difference between spherical indentation tests at room and elevated temperatures into consideration, the incremental and analytical models were used to determine material parameters ( σ0, Ep, and n) and thermal softening parameters ( Eeff and m) in the Johnson–Cook constitutive equation, respectively. A discussion on the stability of the analytical model proved that despite in relative complicated forms and with three intercoupling material parameters, the analytical model is still effective for tensile property calculation. From the investigation on the relationship between pm and pi, it was found that correlating coefficient ξ is actually a function of both indentation depth and material parameters, and thus, a regression function was proposed for a more accurate description of ξ. Effectiveness of the spherical indentation tests was verified through experiments on three steels, SA508, 15CrMoR, S30408, and one titanium alloy, TC21, which proved that the spherical indentation tests can provide both proof and tensile strength calculations with a maximum error around 15% at room temperature and within 20% at elevated temperatures, and thus satisfy the demands for engineering applications.

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