Mini Specimens Research Articles

INFLUENCE OF ROUGH AS-BUILT SURFACES ON SMOOTH AND NOTCHED FATIGUE BEHAVIOR OF L-PBF AlSi10Mg

Near-net shape metal parts of great geometrical complexity are fabricated by the Laser Powder Bed Fusion (L-PBF) technology directly from a CAD model. Therefore, parts can be lightweight, less expensive in terms of material use and with shapes that may be impossible to produce by conventional technology. The fatigue behavior of L-PBF part in as-built condition is negatively affected by poor surface quality. Surface finishing after fabrication may be either unacceptably costly or impossible because the surface is inaccessible. Fatigue performance can be further reduced by the notch effect due to local geometrical variations. Among the Al-alloys, AlSi10Mg is readily processed with L-PBF and it is of interest for different industrial sectors.In this contribution two aspects, that is: i) the directional smooth fatigue behavior of as-built AlSi10Mg, and ii) the notch fatigue behavior with as-built surfaces are investigated. Eight sets of un-notched and notched miniature specimens of AlSi10Mg were produced as a single batch by L-PBF and tested in the as-build state under cyclic plane bending loading. The smooth fatigue behavior was determined as very sensitive to applied stress direction with respect to the build direction. The directional nature of the fatigue behavior was confirmed by notch fatigue data. Therefore, four notch fatigue factors that depend on the PBF technology were introduced and determined. The fatigue behavior of L-PBF AlSi10Mg obtained here was compared satisfactorily against recent data obtained with standard specimen geometries and test methods. The present methodology using mini specimens under cyclic bending efficiently determines the fatigue response of L-PBF metals.

Microstructural characterization and mechanical properties of mini specimen of research reactor fuel cladding

Mini specimens of 5052 alloy have been used to study the mechanical behaviour for cladding materials of research reactor. The problem that arises in the manufacture of the mini specimens is the deformation effect after shear cutting process. The objective of this research is to obtain characteristics of mini specimens of 5052 alloy, i.e. microstructure, hardness and tensile strength. The results have showen that microstructureof fresh 5052 alloy is not homogeneous, but that of as-rolled 5052 alloy is non-homogeneous for elongated flat along the roll direction. In the 250 C heat treatment, the grain structure of as-rolled 5052 alloys is increasingly homogeneous with slight grain size changes as the heating time increases. The hardness of 5052 alloy as-rolled after heat treatment ranges from 39.67 - 40.55 VHN. The hardness of as-rolled 5052 alloy is higher than that of fresh 5052 alloy without and post heat treatment. Tensile strength of as-rolled 5052 alloy after heat treatment is relatively the same, i.e. 159.50 – 160.27 MPa with a strain of 31.67 – 34.58%. Tensile strength of 5052 alloy after mechanical treatment has higher tensile strength than fresh and as-rolled 5052 alloys. The mechanical treatment of as-rolled 5052 alloy could eliminates the shear cutting effect on the surface of mini specimens.

A Displacement Controlled Fatigue Test Method for Additively Manufactured Materials

A novel adaptive displacement-controlled test setup was developed for fatigue testing on mini specimens. In property characterization of additive manufacturing materials, mini specimens are preferred due to the specimen preparation, and manufacturing cost but mini specimens demonstrate higher fatigue strength than standard specimens due to the lower probability of material defects resulting in fatigue. In this study, a dual gauge section Krouse type mini specimen was designed to conduct fatigue tests on additively manufactured materials. The large surface area of the specimen with a constant stress distribution and increased control volume as the gauge section may capture all different types of surface and microstructural defects of the material. A fully reversed bending (R = −1) fatigue test was performed on simply supported specimens. In the displacement-controlled mechanism, the variation in the control signal during the test due to the stiffness variation of the specimen provides a unique insight into identifying the nucleation and propagation phase. The fatigue performance of the wrought 304 and additively manufactured 304L stainless steel was compared applying a control signal monitoring (CSM) method. The test results and analyses validate the design of the specimen and the effective implementation of the test bench in fatigue testing of additively manufactured materials.

Fatigue life prediction of aluminium profiles for mechanical engineering

The study presents a method to determine the a −N curve (high cycle fatigue) for profiles made of AW-6063 T6 aluminium alloy. Experimental material data for a mini specimen taken directly from the tested item and selected empirical correlations allowing for a size effect have been used. A model yielding the lowest relative error of estimating the fatigue life is presented.

Creep test with use of miniaturized specimens

Application of the mini samples methods is very common especially for residual service life assessment of the components operating in the energy sector. Residual lifetime of operating device can be evaluated using standard tests, but these usually cannot be performed due to limited material amount that can be extracted from the components. It is possible to use in these cases a semi destructive sampling of materials and testing methods employing miniature specimens. This article deals with comparison of the creep results obtained with the use of on standard test bars and sub sized samples such as Small Punch Test and newly proposed miniature samples that are axially loaded. The experiment was performed on steam line steel CSN 15 128 after operation. Emphasis was put to practical use of the test results and therefore residual life was assessed with the use of standard and new mini specimens. The results obtained for standard and mini samples exhibit very good agreement without necessity of any correlation as in the case of SPT and thus much more straight forward approach can be applied even for “unknown materials”.

Level of soluble programmed death-1 ligand 1 in peripheral blood of patients with advanced epidermal growth factor receptor mutated lung adenocarcinoma and its clinical implications

Objective: To analyze the expression of soluble programmed death ligand 1 (sPD-L1) in the serum of patients with advanced epidermal growth factor receptor (EGFR) mutated lung adenocarcinoma and to explore its clinical implications. Methods: Seventy-two patients with EGFR mutated advanced lung adenocarcinoma (EGFR mutation group) were included from the Department of Respiratory Diseases in The Second Affiliated Hospital of Soochow University from May 2015 to July 2016. Thirty-one patients with advanced EGFR wild type (WT) lung adenocarcinoma [EGFR WT group, diagnosed via mini specimens from bronchoscopy or transthoracic needle aspiration biopsy (TNAB), matching in sex, age and tumor stage with EGFR mutation group] were also enrolled as controls. The sPD-L1 protein expression in serum was determined by enzyme-linked immunosorbent assay (ELISA) kit. According to the clinical response of two-month EGFR-tyrosine kinase inhibitor (TKI) treatment, all patients were divided into two groups: 36 cases in disease progression groups (PD group) and 36 cases in disease control group (DC group). The sPD-L1 level in peripheral blood between the two groups was analyzed. In EGFR mutation group, the relationship of serum sPD-L1 with TNM staging was analyzed. At the same time, the value of serum sPD-L1 and cancer embryo antigen (CEA) in clinical evaluation of advanced EGFR mutated lung adenocarcinoma was evaluated by analyzing the receiver operating characteristic (ROC) curve. Results: A lower level of sPD-L1 level in EGFR mutation group [0.75(0.15-2.78) μg/L] was found compared with the control group [1.56(0.85-3.29) μg/L] (P<0.001). The expression of sPD-L1 in PD group was significantly higher than that in DC group [1.175(0.62-2.78) μg/L vs 0.625(0.15-2.27) μg/L, P<0.001]. High expression of sPD-L1 in the serum of patients with advanced EGFR mutated lung adenocarcinoma was closely correlated to lymph node metastasis and distant metastasis (χ2=10.985, 4.662; both P<0.05). The area under ROC curve of serum sPD-L1 and CEA was 0.893 (95%CI: 0.830-0.956) and 0.745(95%CI: 0.652-0.839) respectively. Youden index was the maximum when the cutoff value of sPD-L1 was set to 0.815 μg/L, and the sensitivity and specificity were 77.8% and 91.4%, respectively. Conclusions: After EGFR-TKI treatment, the level of sPD-L1 in the serum of patients with advanced EGFR mutated lung adenocarcinoma is lower, which suggests that sPD-L1 expression may depend on the regulation of EGFR signaling pathway. The level of sPD-L1 can reflect the clinical response of EGFR mutated lung adenocarcinoma to EGFR-TKI.

Weibull statistical analysis of Krouse type bending fatigue of nuclear materials

A bending fatigue mini-specimen (Krouse-type) was used to study the fatigue properties of nuclear materials. The objective of this paper is to study fatigue for Grade 91 ferritic-martensitic steel using a mini-specimen (Krouse-type) suitable for reactor irradiation studies. These mini-specimens are similar in design (but smaller) to those described in the ASTM B593 standard. The mini specimen was machined by waterjet and tested as-received. The bending fatigue machine was modified to test the mini-specimen with a specially designed adapter. The cycle bending fatigue behavior of Grade 91 was studied under constant deflection. The S–N curve was created and mean fatigue life was analyzed using mean fatigue life. In this study, the Weibull function was predicted probably for high stress to low stress at 563, 310 and 265 MPa. The commercial software Minitab 17 was used to calculate the distribution of fatigue life under different stress levels. We have used 2 and 3- parameters Weibull analysis to introduce the probability of failure. The plots indicated that the 3- parameter Weibull distribution fits the data well.

Study about Stress-Strain Properties with Mini Specimen and Microstructure of Nuclear Fuel Element Cladding of Al-Alloy (98% Al + 1% Fe + 1% Ni) after Being Tempered at Temperatures between (100 – 650) °C

Stress-strain properties with mini specimen and micro structure of nuclear fuel elements cladding of Al-alloy (98% Al + 1% Fe + 1% Ni) after tempered at temperatures (100-650) °C, for 1 hour have been studied. Al-alloy (98% Al + 1% Fe + 1% Ni) was made for cladding nuclear fuel elements of research reactor. Al-alloy (98% Al + 1% Fe + 1% Ni) as cladding material has been on the rollers and then made a mini specimen tensile test samples. The mini specimen tensile test samples were tempered at temperatures of (100-650) °C, respectively 1 hour. Samples were tested to determine properties of tensile stress-strain with a mini-tensile test specimen. The tensile test equipment can attract maximum sample 5 kN, Shimadzu Autograph AGS-brand artificial 5kN, made in Japan. Then the samples were broken section micro structure observed by SEM (Scanning Electron Microscope). Quantitative results showed that the higher the tempering temperature, the maximum stress is decreased. The higher the tempering temperature cleavage fracture increasingly overlaps (small). This is due to the self-diffusion of Al atoms in the material when the sample tempered at (100-650) °C, for 1 hour. Observation of the microstructure by SEM (Scanning Electron Microscope) was visible presence of porosity in the sample.

Verification of selected models of the size effect based on high-cycle fatigue testing on mini specimens made of EN AW-6063 aluminum alloy

The study presents several cases where use of specimens with reduced overall dimensions, i.e. mini specimens in the course of fatigue tests is advantageous. The high-cycle fatigue tests based on a developed method have been performed on mini specimens and normative specimens (comparative tests). The tests have been conducted on EN AW-6063 aluminum alloy specimens. A correction coefficient determined as a result of monotonic tests and selected models of the size effect have been critically assessed based on the test results. A statistical Weibull's weakest link model and a monofractal approach based on a fractal dimension have been verified.

Verification of the Fatigue Test Method Applied with the Use of Mini Specimen

In special situations the fatigue properties of the construction material can be determined using non-standard specimens, for example smaller than the normative ones (the so-called mini specimens). The research presented was made for the aluminum alloy based on the high-cycle fatigue testing methodology. The verification was made by breaking down the results with own tests which involved the use of standard specimens and stands as well as with the literature reports.

A mini desktop impact test system using multistage electromagnetic launch

A miniaturized Split Hopkinson Bar (SHB) system has been developed based on electromagnetic launch. The novel and simple multistage electromagnetic launch technique has been investigated for being against the drawback of traditional pneumatic loading system, such as the need for very-high air pressures, lack of test repeatability, high operation noise, large size, and large overall weight of the apparatus. The easy and practicable multistage electromagnetic launch device and its working principle are described in details. A simple launch speed calibration technique, methods of eliminating the electromagnetic signal effect and erasing magnetism in bars are also described. With the same multistage electromagnetic launch device and main components, the system could be switched between impact compression and tension modes for mini specimen testing easily. Successful validation tests on aluminum alloy for impact compression and polyimide/SiO2 film for impact tension were carried out for verifying the feasibility and reliability of the system.

Experimental identification of yield surface of Al–Cu bimetallic sheet

Design of structures made form metal layered composite with a gradient variation of physical properties requires knowledge of their behaviour in the small of elasto-plastic strain. The aim of the research was the experimental investigation of these behaviours. Preliminary tests were carried out on standard flat specimens made from aluminium-copper layered composite, which was obtained by rolling process. Each component (layer) in the state before connecting into a composite was tested independently. The test specimens were cut from metal sheets in different directions (in the range 0–90°). The primary strength tests showed a large anisotropy of mechanical properties. Further studies, in the main part, were associated with the investigations of evolution of yield surfaces for Al–Cu bimetal and components in the range of strains from proportional limit to 0.3%. The investigations were realised by monotonic tensile tests of mini specimens, which were cut out in different directions from the large-size specimens and put to the initial deformation 0.75% in the direction of rolling. The method gave possibility to realising tests in the plane stress state and build for aluminium, copper and Al–Cu bimetal experimental yield surfaces. Evolution of yield surface with increasing levels of plastic deformation was studied. Analysis of their shape showed that aluminium, copper and Al–Cu bimetal had isotropic hardening. It was shown that the law of mixtures applied to the determination of the yield surface of Al–Cu bimetal was applicable only in a short range of elasto-plastic deformation (0.05–0.2%) and for specimens cut at an angle 0–45° from the large-size specimen.

20408 Effects of spray conditions and heat treatment on the microstructure and mechanical properties of warm sprayed titanium and Ti-6A1-4V alloy coatings

One of the most interesting applications of thermal spray titanium and its alloys is direct forming because it allows quick production of parts with minimal waste of materials. However, oxidation and porosity are major problems because they degrade mechanical properties of the formed coatings. Warm spray is a coating process developed at NIMS, by which one can control the temperature and velocity of sprayed particles. In this study effects of spray conditions on the microstructure and mechanical properties of Ti and Ti-6A14Vcoatings were investigated. Due to the limitation of available testing materials, mini specimens with total length of about g mm were used to determine their mechanical properties. Additionally, heat treatment was performed in order to enhance the mechanical properties of as sprayed coatings.

Determination of the Fatigue Properties of Aluminum Alloy Using Mini Specimen

There are situations where taking normative specimens is impossible due to the dimensions of the objects investigated (e.g. extruded sections) and one of the solutions is to use mini specimens. As for non-standard specimen testing, it is essential to define the effect of size on fatigue strength. The research methodology facilitates the determination of fatigue characteristics (S-N) for EN AW-6063 aluminum alloy. The material is used to manufacture the extruded section in the process of extrusion of the material through the extruding die. The methodology assumes the geometry of the mini specimen and the normative specimen. As for the material strength identification, a static tensile test for the specimens made directly from finished elements and preliminarily strained in cycles was carried out. As a result of the cyclic material reinforcement, an increase in yield strength Re was observed, which, in turn, rejects Re as the upper criterion of the high-cycle fatigue range. The essential fatigue tests were performed based on unilateral cyclic tension (R = 0.1). The effect of size on fatigue strength was defined. Theoretically aluminum alloy non-sensitive to changes in the size of the cross-section showed a different strength in mini and normative specimens.

Study on Cu particles-enhanced SnPb composite solder

The Sn-Pb solder is widely used in the electronics industry. With the development of surface mount technology and miniaturization of elements, mechanical properties of the solder are critical. Creep resistance and size stability of soldered joints are important for optical electronics. In the present work, Cu particles with a size of about 8 µm were added to the eutectic 63Sn-37Pb solder to improve the creep property of the soldering alloy. The contents of the Cu particles are 5 vol.% and 10 vol.% separately. The solder matrix is 63Sn37Pb particles with a normal size of 43 µm. The composite solder pastes are manufactured from a mixture of these particles with no-clean flux. Under reflow soldering, the metal particles were uniformly dispersed in the Sn-Pb alloy, and very thin intermetallic compounds were formed between the particles and matrix. To simulate practical soldering of printed circuit boards, a specially designed mini specimen with lap joint is used for the creep-rupture test. For the condition of ambient temperature, the creep-rupture lifetime of the soldered joint can be increased by one order quantitatively using the composite solder compared to the 63Sn37Pb eutectic solder. Other mechanical properties are measured also. In addition, the wetting property of the enhanced solder is good through the wettability test.

Fracture toughness of acrylic bone cements

Clinical experience has shown that fracture of PMMA-based bone cements is a significant factor in the failure of orthopaedic joint replacements. Earlier studies of the fracture toughness properties of bone cement have been limited to relatively large test specimens — ASTM standard test methods require the use of specimens with dimensions considerably larger that those associated with bone cement in clinical use. In this study, a miniature short-rod specimen was used to measure the fracture toughness (K IC) or two bone cements (Simplex-P and Zimmer LVC). The dimension of our mini specimens approaches the cross-section of bone cements as usedin vivo. The short-rod elastic-plastic fracture toughness test method introduced by Barker was utilized to ascertain the effect of specimen preparation and ageing in distilled water on fracture toughness. Our study indicated that slow hand-mixed specimens possess comparable fracture toughness to centrifuged specimens. After ageing in water, however, centrifuged and slow hand-mixed specimens are more fracture resistant than specimens prepared by mixing the cement quickly. An optimum void content for the bone cements studied was suggested by the experimental results; for Simplex-P bone cement it appeared to be less than 1.6% whereas it was between 1.6 and 3.6% for Zimmer LVC cement. Simplex-P bone cement also showed superior fracture toughness compared to Zimmer LVC cement after storage in water for 60 days at 37° C.

Short-rod elastic-plastic fracture toughness test using miniature specimens

The standard ASTM-E399 plane-strain fracture toughness (K IC) test requires (1) the test specimen dimensions to be greater than a minimum size and, (2) fatigue precracking of the specimen. These criteria render many materials impractical to test. The short-rod elastic-plastic plane-strain fracture toughness test proposed by Barker offers a method of testing not requiring fatigue precracking and furthermore, it appears that test specimens smaller than that stipulated by ASTM can be used to obtain validK IC values. In this study, the use of a modified miniature short-rod fracture toughness test specimen was investigated. Our miniature short-rod specimen is approximately 7 mm long and 4 mm diameter. These mini specimens are well suited for the purpose of testing biomaterials. The value of the minimum stress intensity factor coefficient (Y m * ) for the mini short-rod specimens was determined experimentally using specimens machined from extruded acrylic rod stock. An elastic-plastic fracture toughness analysis using the mini specimens gave values ofK IC for extruded acrylic (nominally PMMA) equal to 0.67 ± 0.06 MPa m1/2. The problem of testing non-flat crack growth resistance curve materials (such as PMMA) using the short-rod fracture toughness test method is discussed. A modification to the test procedure involving the use of aY * value corresponding to a short crack length is suggested as a method of overcoming this difficulty.