Non-standard Specimens Research Articles

Evaluation of crush performance of extruded aluminum alloy tubes based on finite element analysis with ductile fracture modeling

In this study, the crush performance of four aluminum extrusions are investigated through analysis based on finite element (FE) simulation incorporating experiment-numerical hybrid ductile fracture modeling. Tensile tests on standard and non-standard specimens, coupled with digital image correlation and FE analyses, are employed to establish constitutive models for the materials. The evaluation of crush performance is performed based on both axial crush test and corresponding 3-dimensional FE simulation, which could validate the employed plasticity and fracture laws and predict crush performance indicators with reliable accuracy. Additionally, FE modeling enables thorough analysis of highly non-proportional loading paths and potential crack initiation sites, with the crack formation mechanism elucidated through the evolution of a proposed damage variable. Furthermore, the modified crush performance indicators are newly suggested, which could explain the dependence on both the absorbed energy of tubular extrusion and properties of ductile fracture.

A novel method to calculate the load vs. crack extension curve based on the load vs. load-line displacement curve

In order to obtain the crack growth resistance curve, a typical fracture test must measure the load vs. crack extension (F-Δa) curve. Apart from the basic measurement of the load vs. load-line displacement (F-vLL) curve, additional instruments or tedious test operations such as partial unloading are necessary to measure the amount of crack extension. This paper proposed a novel method of calculating the F-Δa curve directly from the F-vLL curve, in which no additional instrument or test operations are required. The proposed method can be easily applicable to these non-standard specimens. Several examples of C(T) and M(T) specimens are adopted to verify this method. Thus, this method is expected to simplify these available standards for measuring crack length.

Mechanics of woven roving/ mat laminate failure in a quasi-static tensile test

Based on tensile tests of non-standard specimens with large dimensions, an attempt was made to explain the mechanics of failure of woven roving/mat laminates with different numbers of layers. The need to use non-standard specimens in tests resulted from the impossibility of interpreting the processes taking place in tensile specimens in specimens with standard dimensions, the results of which are published in the scientific literature. In the tensile tests, four loading phases were observed, in which in the last two the structure of matrix was failed by micro- and macro-cracks, and finally by delamination through the laminates. To describe the fracture mechanics of the discussed laminates, the principle of energy equivalence was used in the transformation of elastic strain energy into binding energy. Although the processes of laminate destruction occur in the matrix, depending on the number of layers, it was found that two different processes of destruction of the internal structure with three variants of elastic strain energy distribution lead to the final delamination of the laminates. The use of energy to describe the failure of laminates in the third phase of specimen loading leads to the definition of such concepts as the dominance of failure stresses and the dominance of failure strains in the process of cracking the laminate structure. Experimental studies indicate a gradient distribution of binding energy towards the center of unloaded specimens, assumed on the basis of a literature review.

Influence of specimen slenderness and stacking on the experimental strength of solid fired clay bricks

This study evaluates the effect of the specimen’s slenderness and stacking on the experimental measurement of the compressive strength of solid fired clay units. The experimental campaign has focused on two different types of solid fired clay bricks, namely mechanically extruded and handmade, with a total amount of 382 specimens tested. The research considers different standard and non-standard specimens with varying width (40, 50, 60, 70, 80, 90, and 100 mm) and height (40, 80, and 120 mm). The experimental results evidence the influence of the stacking procedure on the compressive strength, with different results depending on the manufacturing process of the unit. The influence of specimen’s slenderness on the compressive strength is more evident and regular in handmade brick specimens than in extruded ones.

Relationship between Rock Porosity and Infrared Cooling Rate in Non-Standard Specimens of Tuffs Used in the Hungarian Cultural Heritage

This paper is focused on the application of Infrared Thermography to non-standard rock specimens, in terms of size and deterioration conditions, of Hungarian tuff to monitor their cooling process and to look for a relationship between the rock Cooling Rate Index and the porosity. Literature data agree on the potential of Infrared Thermography for the indirect estimation of rock porosity in fresh specimens through the IRTest, but this technique has never been tested on non-standard specimens. To this purpose, tests on three varieties of Hungarian tuffs were carried out. These materials were selected for their cultural importance linked to their usage as building stones and in other historical applications in Northern Hungary. Tuff specimens underwent a fixed number of salt crystallization cycles. The Cooling Rate Index (CRI) for each specimen was calculated according to the literature experience and correlated to their porosity estimated by water, helium, and mercury intrusion. The results show that the rock cooling process is related to porosity since more porous rocks are characterized by faster cooling. Positive linear trends were achieved for weathered specimens considering 20 min monitoring (CRI20), which is double the time suitable for untreated rocks. The reason should be searched in salt crystallization’s effects on the rock texture, paving the way to further studies on this pioneering branch of technological application.

Assessment of Additive Manufactured IN 625's Tensile Strength Based on Nonstandard Specimens.

The study aimed to evaluate the tensile strength of additively manufactured (AMed) IN 625 using sub-sized test pieces and compare them to standard specimens. Cylindrical round coupons of varying diameters were manufactured along the Z-axis using the laser powder bed fusion technique and subjected to heat treatment. The simulation of the alloy solidification predicted the formation of several intermetallics and carbides under equilibrium conditions (slow cooling), apart from the γ phase (FCC). Sub-sized tensile specimens with different gauge diameters were machined from the coupons and tensile tested at ambient temperature. The results showed that sub-sized specimens exhibited lower tensile and yield strengths compared to standard specimens, but still higher than the minimum requirements of the relevant ASTM standard for AMed IN 625. The lower strength was attributed to the "size effect" of the test specimens. Fracture surfaces of the sub-sized test specimens exhibit a mixed character, combining cleavage and microvoid coalescence, with improved ductility compared to standard test pieces. The study highlights the importance of adapting characterization methods to the particularities of manufactured parts, including reduced thicknesses that make sampling standard-size specimens impractical. It concludes that sub-sized specimens are valuable for quality control and verifying compliance with requirements of AMed IN 625 tensile properties.

Experimental study on size of aggregates, size and shape of specimens on strength characteristics of pervious concrete

Pervious concrete has a wide range of applications including pervious pavements, rigid drainage layers and water-free floor. In this paper, the influence of aggregate size, shape, and size of specimens on the mechanical properties of pervious concrete has been investigated. Tests on pervious concrete include direct compression on cubes and cylinders, splitting tension, and flexural tests on respective cylinders and prisms were carried out on three different mixes with aggregate sizes of 10, 12.5, and 20 mm. The height of specimens was kept as the primary variable whereas the aspect ratio was kept constant. Experimental results indicated that when aggregate size and height of specimen increases, compressive, splitting tensile and flexural strength decreases. Using Size effect models such as Linear model, Bažant's Size Effect Law and Modified Size Effect law, an approach is proposed to predict non-standard specimen strength from known standard specimen strength with high accuracy.

Size Effect on the Post-Necking Behaviour of Dual-Phase 800 Steel: Modelling and Experiment

This work investigated the feasibility of using a miniaturised non-standard tensile specimen to predict the post-necking behaviour of the materials manufactured via a rapid alloy prototyping (RAP) approach. The experimental work focused on the determination of the Lankford coefficients (r-value) of dual-phase 800 (DP800) steel and the digital image correlation (DIC) for some cases, which were used to help calibrate the damage model parameters of DP800 steel. The three-dimensional numerical simulations focused on the influence of the size effect (aspect ratio, AR) on the post-necking behaviour, such as the strain/stress/triaxiality evolutions, fracture angles, and necking mode transitions. The modelling showed that although a good correlation can be found between the predicted and experimentally observed ultimate tensile strength (UTS) and total elongation. The standard tensile specimen with a gauge length of 80 mm exhibited a fracture angle of ∼55°, whereas the smaller miniaturised non-standard specimens with low ARs exhibited fractures perpendicular to the loading direction. This shows that care must be taken when comparing the post-necking behaviour of small-scale tensile tests, such as those completed as a part of a RAP approach, to the post-necking behaviours of standard full-size test specimens. However, the modelling work showed that this behaviour is well represented, demonstrating a transition between the fracture angles of the samples between 2.5 and 5. This provides more confidence in understanding the post-necking behaviour of small-scale tensile tests.

Manufacturing of testing specimens from tough HDPE-100 pipe: Turning parameters optimization

Numerous machining operations are required in order to manufacture standard and non-standard specimens for mechanical testing of polymers. The present work focuses on the machinability of HDPE-100 pipe to prepare the utmost regular filaments with specified thickness and width. The study is set to establish mathematical correlations between surface quality (total roughness; Rt), cutting temperature (T°), filament uniformity (L) and corresponding cutting conditions. The latter include Vc (cutting speed), f (feed rate) and ap (depth of cut), combined with tool geometry (i.e., rake angle: γ and cutting-edge angle: κr). A mixed Taguchi L18 plan is adopted to organize and process the experimental runs. ANOVA and RSM (Response Surface Methodology) are employed to construct prediction models and optimize subsequent machining results. It is found that T (cutting temperature) and surface roughness criteria (Ra, Rt) are strongly affected by f and Vc. In addition, ANOVA results related to the height of filament bends (L) are likewise studied as a function of tool angles γ and κr. It is noted that cutting process is influenced by κr as it explains ~19% contributions of the total variation of parameter L, while γ, Vc and f show a little influence. It is deduced that optimum input parameters, represented by Vc, f, ap, γ and κr, are respectively 160 m/min, 0.5 mm/rev, 4 mm, (-6°) and 90° when turning tough HDPE material.

A deep learning-based fatigue crack growth rate measurement method using mobile phones

This paper proposes a fatigue crack growth rate (FCGR) measure method based on deep learning. Crack data sets of different scales are first collected by a camera, and are then used to train the faster region-based convolutional neural network (Faster R-CNN), respectively. A novel global and local dual-scale Faster R-CNN is further constructed and integrated into the mobile phone to predict the crack length during the entire loading cycle. The fatigue crack growth rate constants are finally obtained by integrating fracture mechanics. The proposed method can effectively measure the propagating small cracks during cyclic loading and extend to non-standard specimens.

Experimental investigation of crack initiation and crack propagation in aluminum demonstrator specimens

The reliable application of complex simulation models to represent crack initiation and propagation in structural components requires an in-depth experimental investigation of the failure behavior. As part of these analyses, the applicability of standard methods of the linear-elastic fracture mechanics to non-standard specimen geometries was investigated. Furthermore, crack growth gauges were used to detect crack initiation and crack growth. Thus, the failure behavior of a demonstrator specimen of an aluminum alloy (EN AW-2024-T351), which is widely used in metal construction and mechanical engineering, could be investigated.

The development of miniature tensile specimens with non-standard aspect and slimness ratios for rapid alloy prototyping processes

This work aims to evaluate the use of miniaturized tensile specimen (MTS) to characterise the mechanical properties of alloys developed through rapid alloy prototyping (RAP), where high throughput tests are required on relatively small amounts of material. Tensile tests were conducted at a variety of strain rates and with increasingly smaller specimen sizes, ranging from larger specimens conforming to ASTM/ISO standards, down to small non-standard specimens. The gauge lengths of the specimens ranged from 50 to 80 mm for the standard specimens down to 5–10 mm for the non-standard specimens. To generalize the non-standard MTS designs, three alloys, DP800, DP600 and 316L stainless steel, were adopted. The results obtained from non-standard designs were compared with those from standard designs. The results show that non-standard designs can give repeatable results for yield strength (YS), ultimate tensile strength (UTS) and uniform elongation (eU). The maximum result differences of YS, UTS and eU are 7.37%, 7.71% and 11.9%, respectively, for DP alloys comparing standard and non-standard dimensions. These values are 13.56%, 14.03% and 19.5%, respectively 316L steel. The total elongation (ef) increases as the specimen dimension decreases. The geometrically dependent constants (n) are 0.2, 0.31 and 0.11 for DP800, DP600 and 316L, respectively. However, the Young's modulus is hard to determine precisely from the miniaturized designs. The conclusion from this work is that miniaturized tensile testing can be used with confidence as a high throughput means of predicting standard mechanical properties across a range of steels.

The Prediction Model of the Correction Coefficient of Concrete Strength is Tested based on the Method of SPSS Regression Analysis

With the regression analysis of SPSS software, the diameter and the ratio of height to diameter were included into the control variables, and the prediction model of the correction coefficient between the non-standard specimen and the standard specimen was established when the C25 pumping concrete was used to test the strength of concrete by drilling core method.

Effect of Specimen Geometry on Selected Physical and Mechanical Properties of Epoxy-Based Building Materials

The paper deals with problematics of the influence of size and shape of test specimens prepared according to the valid standard procedures in comparison to specimens prepared according to the standards used for different types of materials (grouts, coatings). The aim of this paper is to verify the possibility of using non-standard specimen sizes to reduce the economic demands of the development of building materials. The issue is tested on the polymer composites prepared in three different amounts of the filler. The polymer composite based on epoxy resin serves as a representative and homogenous material which achieves the same results under various curing temperatures and humidity. The porous structure of prepared samples was also studied and its effect on the selected mechanical properties was observed. It was shown that the specimen shape and size had impact on the mechanical properties of epoxy-based composites.

A virtual fields method for identifying anisotropic elastic constants of fiber reinforced composites using a single tension test: Theory and validation

A novel inverse identification method using only a single tensile specimen for obtaining four anisotropic elastic constants of fiber reinforced composites sheet is proposed in this study. The method is based on virtual fields method (VFM) for solving weak form equilibrium equation with an optimized tension-type non-standard specimen specially designed with an elliptic hole at the center of the specimen (though not limited to this special shape). Full-field strain measured by a digital image correlation (DIC) technique is applied as experimental strain fields which are used as inputs of the VFM. For optimizing the tension-type VFM specimen, finite element (FE) analysis is conducted as a virtual experiment to generate ideal strain fields. The determined tension-type VFM specimen has an elliptic hole with 45° inclined to the loading direction, which is optimized from the error analysis between the FE input and VFM calculated material constants. For the validation of the proposed approach, experiments are performed with unidirectional carbon fiber reinforced plastic (UD-CFRP) sheets. The comparison of VFM identified anisotropic constants to those determined from the standard tensile tests with three different orientated samples shows satisfactory accuracy ranging between −5.94 and 0.71%, errors which confirm the validity of the new inverse method for the characterization of anisotropic elasticity of composites sheets.

Characterization of sticky-rice lime binders from old masonry relics in north China: The primary contribution for conservation

The application of traditional organic-inorganic composite lime-based materials, particularly sticky-rice lime binder, in sustainable restoration for old buildings, has attracted increasing attention in last decades. In present study, series of sticky-rice lime binders, sampled from thirteen old masonry relics involved three regions in 16–19th century, were fully characterized as primary. Specifically, micro-mineralogical and chemical characterization were determined by conducting XRD, FTIR, DSC-TG, SEM, iodine-starch and acid test, also mechanical-physical properties based on non-standard specimens including SH, UPV, CS, Po, Ccc D1 and D2. Furthermore, direct or inexplicitly relationships between organic content and enhanced physical-mechanical indicators were established. Finally, characterization results were analyzed and compared with deep gathering datasets from literature respecting characteristics of these binders of 6–19th century. Those analysis results provide valuable information for composite lime materials to expanding the database for formulating lime-based binders used in repairing intervention.

Performance of 316L Stainless Steel Diffusion Welding during High Temperature Creep

The creep and rupture test were carried out on a non-standard specimen of 316L stainless steel (316L-SS) diffused bonding joint. And the θ-projection model was used to analyze the minimum creep strain rate and the remaining life at 500°C/6 MPa when the creep strain is 0.2%. According to the test results, design criterion for the diffusion bonding component at high temperature is established. The rupture experimental results show that the remaining life extrapolated by Larsen-Miller equation is relatively consistent with that calculated by the θ project concept method.

Effect of defects and specimen size with rectangular cross-section on the tensile properties of additively manufactured components

ABSTRACT To evaluate specimen size dependence on the tensile properties of additively manufactured (AM) components, various rectangular specimens, ranging from miniaturised to ASTM standard specimens, are machined from electron beam melted Ti-6Al-4V and used for the tensile testing. It is found that the elongation is strongly related to the sample size while the yield and ultimate tensile strengths exhibit an independent feature. Three major aspects, (i) presented location of lack of fusion, (ii) size and segregation of pores, and (iii) slimness ratio, have a synergic influence on the elongation of different specimen sizes with various cross-section area. Our findings suggest that microscale tests arise uncertainties in measurement, which must be considered in order to provide quantifiable levels of confidence when applying such tests to discriminate a material’s behaviour. The experimental results and analyses provide a guideline for the design and testing of non-standard specimens for AM components.

Performance assessment of custom-made replications of an original historic render – A study of application influences

This performance study focuses on a custom mortar designed and produced as a material and technological copy of an original. The study was carried out in order to determine mortar properties and evaluate influences on practical application. Two mixing water amounts and four different floating compaction levels were compared. The influence of a limewash coating was also studied. The assessed performance properties were related to water transport mechanisms and mechanical strength. The properties were determined on standard specimens cast in steel moulds according to the EN 1015 standard. In order to also be able to take into account the application effects, render panels 60 cm × 60 cm were prepared. The mortar was made of natural hydraulic lime slaked to powder mixed with locally dug sand in 1:1 vol ratio. The specimens were cured in laboratory conditions with regular weekly wetting, and were tested at the age of 120 days. The assessed physical properties were open porosity, 24-hour absorption, capillary absorption, unidirectional drying, water vapour permeability, compressive and flexural strength. In addition, carbonation degree was quantified by thermal analysis. XRD QPA was used to confirm the carbonation. Unhydrated hydraulic compounds were not identified by the XRD; only amorphous content was quantified. SEM observation confirmed the presence of hydraulic compounds. All tests were carried out on the standardised prisms as well as on the non-standard specimens cut from the render panels. This allowed for determination of not only the average properties but also their approximate ranges due to the various application factors. The determined properties were proportionally comparable with other NHL mortar mixes. This confirmed that the mortar designed as a material and technological copy is generally applicable for restoration works, and the results provided the basic data for the assessment of its suitability. The experiments showed that the most crucial influential factor was the initial moisture content which affected all the studied properties. The higher compaction increased the compressive strength and decreased open porosity. The compaction was applied as repeated floating of the surface, and this also had a significant effect on the reduction of plastic shrinkage cracking. The floating alone closed the surface pores and changed its properties in comparison with the rest of the mortar. It strongly affected the drying and permeability properties that were up to 4 to 5 times higher for the panels than that of the standard specimens. Curious behaviour was observed on the limewash coated surfaces. The limewash diminished the closing effect of the floating and relatively increased the drying and permeability. The results obtained on the panels differed from that of those determined on the standard specimens. The differences between the properties of standard and non-standard specimens are discussed.

The influence of torsion effect on fracture behavior of Pipe Ring Notched Bend specimen (PRNB)

Through the time, researches realize the problem of inability to measure the fracture toughness of pipe material in some cases, because of inability of producing standard specimens from pipe wall. This problem is especially expressed in thin walled pipes. In that sense, a lot of alternative procedures and nonstandard specimens are proposed but with no notable success. One of the latest and the most convenient one is Pipe Ring Notched Bend specimen (PRNB) proposed by Gubeljak and Matvienko (Patent No. RU 2564696 C1, 10.10.2015.: Matvienko Y.G. and Gubeljak N., Model for Determination of Crack – Resistance of the Pipes). Lot of research are made on the PRNB specimen and this paper presents further analysis of such a specimen. Due to the specific geometry of PRNB specimen and loading which is three – point bending, torsion effect occurs in the region of crack. This paper deals with analysis of influence of this torsion effect on fracture behavior of PRNB specimen. In order to obtain more detailed analysis of torsion effect influence, J – integral versus thickness of the specimen curves are presented for the specimen with and without torsion effect and for various a/W ratios. Further, comparison of maximal J – integral values (at half of wall thickness B/2) for specimens with and without torsion effect in relation to the a/W ratio has been analyzed.