An overview of mechanical and physical testing of composite materials

Northward. Saba , ... M.T.H. Sultan , in Mechanical and Concrete Testing of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites, 2019

ane.2.three.one Charpy touch on

The Charpy bear upon test was invented in 1900 by Georges Augustin Albert Charpy (1865–1945), and it is regarded every bit one of the most normally used examination to evaluate the relative toughness of a material in a fast and economic way. The Charpy bear on examination measures the energy absorbed by a standard notched specimen while breaking under an bear upon load. This examination continues to be used as an economic quality control method to decide the notch sensitivity and touch on toughness of engineering materials such equally metals, composites, ceramics, and polymers. The standard Charpy impact exam specimen is of dimension 55  mm   ×   x   mm   ×   x   mm, having a notch machined across one of the larger dimensions, as illustrated in Fig. 1.iii. The Charpy impact test measures the free energy absorbed by a standard notched specimen while breaking nether an affect load [10]. This test consists of striking a suitable specimen with a hammer on a pendulum arm while the specimen is held deeply at each terminate. The hammer strikes opposite the notch. The energy absorbed by the specimen is determined precisely by measuring the decrease in motion of the pendulum arm. The of import factors that bear upon the toughness of a textile include low temperatures, loftier strain rates (by bear upon or pressurization), and stress concentrators such as notches, cracks, and voids: http://www.wmtr.com/en.charpy.html.

Figure 1.iii. Charpy impact examination.

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Stress and reliability analysis for interconnects

Hengyun Zhang , ... Wensheng Zhao , in Modeling, Analysis, Design, and Tests for Electronics Packaging across Moore, 2020

4.2.4.1.iii Charpy touch test and analysis

The Charpy touch on test helps determine the touch on energy absorbed and failure mode. 2 different Charpy specimens of bulk Sn–Ag–Cu specimen and soldered specimen as shown in Fig. 4.ii.75 are used in the test. For soldered specimen, two copper blocks are soldered together with Sn–Ag–Cu solder after reflow procedure. Two cases are studied for soldered specimen: copper block with and without Ni/Au plating. Three samples are tested for each type of Charpy specimen. Fig. 4.2.76 shows the fracture modes for different specimens. The bulk specimen exhibits ductile failure, and soldered specimen shows all breakable interface failure. Table 4.two.fifteen lists the affect toughness for dissimilar specimens. The bulk solder specimen has the largest toughness value. The impact toughness of soldered specimen without Ni/Au plating is twice higher than that with Ni/Au plating. It implies that electronic associates with Sn–Ag–Cu solder and Ni/Au end is liable to bear upon failure compared with the case without Ni/Au finish, which is consequent with drop test results for the PBGA parcel mentioned above. Cu/Sn IMC is formed between copper block and Sn–Ag–Cu solder, while Cu-Ni-Sn IMC is formed when Ni/Au plating is used. The Charpy impact test results testify that when the drop failure style shows IMC breakable failure, bundle with ENIG lath surface finish has lower drib lifetime than that with OSP lath surface finish.

Effigy 4.2.75. Charpy impact exam specimens: (a) soldered specimen, and (b) bulk Sn–Ag–Cu specimen.

Figure four.2.76. Failure way under Charpy impact test: (a) breakable failure for soldered specimen, and (b) ductile failure for majority Sn–Ag–Cu specimen.

Table 4.2.15. Impact toughness for dissimilar specimens.

Specimens Bulk Sn–Ag–Cu Soldered sample without Ni/Au Soldered sample with Ni/Au
Impact toughness (J) 74.0 0.261 0.118

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Testing of Safe Lining

Chellappa Chandrasekaran , in Anticorrosive Rubber Lining, 2017

Charpy Touch on Examination

The Charpy impact examination, also known as the Charpy 5-notch examination, is a standardized high strain-charge per unit test that determines the amount of energy absorbed by a material during fracture. This captivated energy is a measure of a given textile'due south notch toughness and acts as a tool to written report temperature-dependent ductile–breakable transition. It is widely applied in manufacture, since it is easy to prepare and conduct and results tin can be obtained quickly and cheaply. The test was developed effectually 1900 past Due south.B. Russell (1898, American) and Georges Charpy (1901, French). The examination became known every bit the Charpy test in the early 1900s because of the technical contributions and standardization efforts past Charpy.

This test helps to determine the material resistance to affect from a swinging pendulum. This exam provides comparative values for various plastics easily and quickly. Test method: ISO 179.

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Characterization

Syed Ali Ashter , in Thermoforming of Single and Multilayer Laminates, 2014

7.two.ane Charpy

The Charpy bear on test is performed to evaluate the resistance of plastics to breakage by flexural shock according to standard test method ASTM D6110 [7]. It indicates the corporeality of free energy needed to break standard test specimens nether specific conditions of specimen, mounting, notching and pendulum velocity at affect.

As shown in Fig. 7.12, the pendulum impact machine consists of a base of operations that holds a pair of supports that holds the specimen. These supports are connected through a rigid frame and bearings, one of a number of pendulum-type hammers with a given initial energy suitable for utilize with a item specimen, a pendulum holding and release machinery and a mechanism for indicating the breaking energy of the specimen. The specimen anvil, pendulum and frame are rigid to maintain correct alignment of the hit border and specimen, both at the moment of impact and during the propagation of the fracture, and to minimize free energy losses due to vibration. The constructive length of the pendulum is betwixt 0.325 and 0.406   1000 and so that the required superlative of the striking nose is obtained by raising the pendulum to an bending between 60° and 30° above the horizontal.

Figure 7.12. Charpy impact test setup [12,thirteen].

Fig. 7.13 shows dimension of a Charpy-type examination specimen as specified in the standard test method [12]. All the specimens are notched at an bending of 45±1° with a radius of curvature at the apex of 0.25±0.05   mm. The airplane bisecting the notch angle is perpendicular to the face up of the examination specimen within 2°. The depth of the plastic material remaining in the bar nether the notch should be x.2±0.05   mm.

Figure seven.13. Dimensions of Charpy blazon test specimen [12].

Specimens of specified material are molded with width between three.00 and 12.7   mm, and one dimension less than 12.7   mm should have the notch cut on the shorter side. When preparing specimens from a canvass material, the specimens are cut from the sheet in both the longitudinal and motorcar directions unless otherwise stated. If the sheet thickness is between 3.0 and 12.vii   mm, the width of the specimen is the same equally the thickness of the sheet. Sheets with thickness greater than 12.7   mm are machined down to 12.7   mm.

Test specimens are conditioned at 23±ii°C and 50±five% relative humidity for at least forty hours subsequently notching and prior to testing. Molded specimens of hygroscopic material are stale as per standard drying procedures (ASTM D4066). Information technology is of import to limit exposure to air during notching and seal the specimens in a water-vapor impermeable container. A minimum of 5 and preferably 10 or more specimens are tested for individual determinations of bear upon resistance besides as to determine the average bear on resistance.

The test specimens are mounted horizontally on the supports and against the anvils to take an impact on the face opposite the notch. The centering jig is used to align the notch between the anvils. The pendulum is then raised and secured in the release machinery. At this bespeak, the calibration on the excess free energy indicating machinery is zeroed. The pendulum is and then released from its release machinery, striking the edge of the pendulum to bear on the specimen. The calibration records breaking free energy and is used to calculate the net breaking energy. If this energy value is greater than 85% of the pendulum's nominal energy, it means the wrong pendulum was used. The results are discarded and the pendulum is replaced by another pendulum with a higher available energy value. The examination is then repeated on a new specimen. In one case all the specimens for a given material take been tested, the bear upon resistance, in joules per meter, for the specific material is calculated [12].

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Fundamental Theories and Mechanisms of Failure

A. Pineau , T. Pardoen , in Comprehensive Structural Integrity, 2007

2.06.4.three.one Introduction

Modeling the Charpy touch exam is a challenging issue, since several aspects of this exam require a detailed analysis. They include: (one) the inertial effects, (ii) the complexity of the loading at high impact charge per unit (five  yard   s−1) and the boundary conditions, (iii) the event of loftier strain rates on constitutive equations, (4) the nonisothermal character of the test, (5) the 3-D aspect of the fracture beliefs, in particular the tunneling consequence associated with DCG preceding cleavage fracture above the lower-shelf temperature, and (6) the competition between ductile and brittle fracture. Yet, recent developments in the instrumentation of the Charpy test largely facilitates the job. Moreover, contempo developments in the local arroyo to fracture take also evolved the Charpy V impact test from a purely quality control test to an evaluation tool for structural integrity cess of materials. Equally already stated in the introduction of this part, a recent briefing has been devoted to this test (François and Pineau, 2001).

It is out of the scope of this chapter to review in detail the models used to simulate the Charpy examination and to calculate the Charpy free energy (CVN). This is already presented in Chapter 7.05. This review was largely based on the work by Tanguy (2001). Further details can also be found elsewhere (Tanguy et al., 2002a, 2002b, 2002c, 2005a, 2005b). Here the focus is laid on salient features in modeling Charpy impact tests. As well the work by Tanguy (2001), other studies should too be mentioned, in particular those by Rossoll (Rossoll, 1998; Rossol et al., 1999, 2002a, 2002b) and those published past the Freiburg grouping (Böhme et al., 1992, 1996; Schmitt et al., 1994, 1999, 1998; Sun et al., 1995). Other theoretical studies just without detailed comparisons with experiments should likewise be indicated (Mathur et al., 1993; Tvergaard and Needleman, 1988, 2000; Needleman and Tvergaard, 2000). Afterward the assay of the salient features arising from those studies, an attempt is made to underline how modeling Charpy V exam can be used to investigate the fracture backdrop of materials under specific conditions, in particular those found with irradiated materials.

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Mechanical Behaviour of Plastics

R.J. Crawford BSc, PhD, DSc, FEng, FIMechE, FIM , in Plastics Engineering (3rd Edition), 1998

2.22.5 Fracture Mechanics Arroyo to Touch

In recent years impact testing of plastics has been rationalised to a certain extent past the utilise of fracture mechanics. The most successful results have been accomplished by assuming that LEFM assumptions (majority linear rubberband behaviour and presence of sharp notch) use during the Izod and Charpy testing of a plastic.

During these types of test information technology is the energy absorbed at fracture, Uc , which is recorded. In terms of the practical force, Fc, and sample deformation, δ, this volition be given by

(ii.121) U c = 1 2 F c δ

or expressing this in terms of the compliance, from equation (two.90)

(2.122) U c = 1 2 F c two C

At present, from equation (2.91) we have the expression for the toughness, Gc, of the material

One thousand c = F c ii 2 B ∂ C ∂ a

So using equation (2.122) and introducing the material width, D

(2.123) Chiliad c = U c B D ϕ

where ϕ = ( ( 1 / C ) ( ∂ C / ∂ a ) ) − 1 . This is a geometrical role which can exist evaluated for any geometry (usually past finite element analysis). Fig. 2.83 shows the preferred test geometry for a Charpy-blazon examination and Tabular array 2.3 gives the values of ϕ for this test configuration. Other values of ϕ may be determined by interpolation.

Fig. 2.83. Charpy test piece

Table ii.3. Charpy calibration gene (ϕ)

ϕ Values
a/D S/D = iv S/D = six Southward/D = 8
0.06 1.183 1.715 two.220
0.ten 0.781 ane.112 1.423
0.20 0.468 0.631 0.781
0.xxx 0.354 0.450 0.538
0.forty 0.287 0.345 0.398
0.fifty 0.233 0.267 0.298
0.threescore 0.187 0.205 0.222

It is apparent from equation (2.123) that a graph of BDϕ against fracture free energy Uc (using unlike scissure depths to vary ϕ) will exist a directly line, the slope of which is the material toughness, Chiliadc.

Case ii.23

A series of Charpy bear on tests on uPVC specimens with a range of fissure depths gave the post-obit results

Crack length (mm) 1 2 3 4 5
Fracture Energy (mJ) 100 62 46.five 37 31

If the sample section is 10 mm × 10 mm, and the support width is xl mm summate the fracture toughness of the uPVC. The modulus of the uPVC is 2 GN/one thousand2.

Solution

Since B = D = ten mm and using the values of ∅ from Table 2.3 nosotros may obtain the following data.

a(mm) a/D ϕ BDϕ U(mJ)
1 0.ane 0.781 78.one × x–vi 100
2 0.2 0.468 46.8 × ten–6 62
3 0.3 0.354 35.4 × 10–6 46.five
4 0.4 0.287 28.7 × x–6 37
5 0.5 0.233 23.3 × ten–6 31

A graph of U against BD∅ is given in Fig. 2.84. The slope of this gives Gc = i.33 kJ/chiliadii.

Fig. 2.84. Plot of Uc against BDϕ

Then from equation (2.108) the fracture toughness is given by

K c = Eastward G c = 2 × 10 9 × 1.33 × x 3 = 1.63 MN 1000 − 3 / two

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Class 92 creep-force-enhanced ferritic steel

Y. Hasegawa , in Coal Power Institute Materials and Life Assessment, 2014

ii.5.2 Toughness

The toughness of Gr.92 steel is evaluated by the Charpy bear on exam every bit per JIS Z 2242 with the dimension of 10  mm square in cross-section and ii   mm depth 5-notch as the full-size specimens. Figure 2.ten shows the transition of captivated energy and the crystallinity according to the Charpy impact test after x to 10 000   h exposure at 600°C. Figure 2.11 likewise represents the transition of the Charpy absorbed free energy and the crystallinity at 650°C for up to 10 000   h. According to the EN standard, Charpy absorbed energy is specified every bit 47   J or higher for specimens sampled from the longitudinal direction, and as 27   J or higher for specimens sampled from the transverse direction. Both Fig. two.10 and Fig. ii.eleven meet the specification for longitudinal sample specimens even after 10 000   h ageing at both 600°C and 650°C.

ii.ten. Charpy absorbed energy and crystallinity transition past aging at 600°C.

2.11. Charpy absorbed energy and crystallinity transition by ageing at 650°C.

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Blend 263

A. Di Gianfrancesco , in Materials for Ultra-Supercritical and Advanced Ultra-Supercritical Power Plants, 2017

17.11 Chemistry optimization

Long-term creep strength is as well required for A-USC applications, and unfortunately Alloy C-263 shows η-phase (an intermetallic phase: Ni3Ti) precipitation after long-fourth dimension exposure between 700°C and 900°C, which is detrimental for long-term creep properties. In the frame on NextGenPower project, the limerick of Blend C-263 was thus optimized to overcome the formation of η-stage. Trial tests were made to study the consequence of hardening contribution elements on microstructural and mechanical properties. Then, a 500-mm-diameter forged rotor was fabricated from optimized 263 alloy and shows promising properties.

As the phase is formed at the expense of the hardening gamma prime phase and the η precipitates are large platelets extending across grains, the η phase generally has an event on long-term creep behavior in superalloys, every bit simply shown in Figs. 17.6 and 17.eight. In this context, Aubert & Duval has focused its research on development of a new alloy based on A263 composition with higher microstructure stability at 750°C while keeping the processing properties of A263 [xviii].

Three conditions were defined to optimize the Blend C-263 composition. The showtime condition was defined to amend microstructure stability at 750°C and so to remove η phase formation. Then, the second and third conditions concern process properties (workability, weldability, etc.), which were expected to be equally good equally those of Nimonic C-263. To satisfy these conditions, γ′ solvus and γ′ content at 750°C accept to be like to those of Nimonic C-263. As we know, formation of η and γ′ phases are linked to Ti and Al contents. Consequently, Thermo-Calc software with the database TCNI5 was used to ascertain Ti-Al couples that satisfy the previous conditions. The stability window of η stage for Nimonic C-263 composition as a function of Ti and Al contents was adamant, and the boundary of the domain is plotted on Fig. 17.22 (dash line). The Ti-Al couple for Nimonic C-263 is as well reported on Fig. 17.22, and information technology appears that Nimonic C-263 lies in the stability window for η stage. Nimonic C-263 γ′ solvus calculated by Thermo-Calc was constitute to be equal to 900°C. Simulations were then made to determine all Ti-Al couples, which let 900°C every bit γ′ solvus, and the results were plotted on Fig. 17.22 (solid line). Nimonic C-263 γ′ content was calculated to be equal to 10   at% at 750°C.

Figure 17.22. Thermo-Calc simulations to ascertain stability window of η stage, γ′ solvus, and γ′ content at 750°C [eighteen].

Equally for γ′ solvus, Ti-Al couples that let 10   at% of γ′ content at 750°C were adamant and plotted on Fig. 17.22 (dash line). Simulations were also performed for 9   at% and eleven   at% γ′ content at 750°C to surround the x   at% line.

The best compromise was then called for the optimized limerick: limerick in the surface area without η formation, with a γ′ solvus of 900°C and a γ′ content at 750°C of near 10 at%. Ti-Al contents were then divers as %Al of 0.83 +/−0.05 and % Ti of 1.53 +/−0.05 (cross on Fig. 17.22).

Tabular array 17.6 summarizes the variation in the chemistry for A263 optimized composition respect to the original formulation.

Table 17.half-dozen. Experimental compositions of tested alloys (weight percent) [18]

Ni Cr Co Mo Ti Al C
C-263 Bal 19.7 20 5.8 2.2 0.42 0.05
Optimized alloy Bal xix.7 twenty 5.ix 1.53 0.79 0.05
Industrial bandage Bal 19.viii 20 half-dozen.i 1.51 0.78 0.05

The main goal was the improvement of creep backdrop of standard A263 true to the improvement of the microstructural stability. Fig. 17.23 shows that the microstructure of the new version is finer than the original, with a population of γ′ with dimension in the range of 22   nm (Fig. 17.24). After aging at 750°C for 3000   h, merely γ′ phase is present, without η germination (Fig. 17.25).

Figure 17.23. Optical micrographs of experimental alloys. (a) alloy 263; (b) optimized alloy [18].

Figure 17.24. FEG-SEM micrographs after heat treatment: secondary γ′ precipitates (around 22   nm) [19].

Figure 17.25. FEG-SEM micrographs after 3000   h/750°C [19].

Mechanical and creep properties are summarized in Fig. 17.26:

Figure 17.26. : Touch strengths and creep results on C-263 and optimized alloy without and with over-aging at 750°C/3000   h [eighteen].
•

Charpy bear on tests and pitter-patter tests 750°C/250  MPa were performed on over-aged samples 50°C/3000   h.

•

Results were compared with results obtained on non-over-aged samples.

•

For optimized alloy, long-term aging at 750°C has no event on touch on forcefulness, whereas information technology is highly decreased for standard A263.

•

Higher influence of long-term aging on pitter-patter rupture life of standard A263 than for Optimized alloy was observed.

•

Subtract of mechanical properties of standard A263 is mainly caused by η phase atmospheric precipitation.

Table 17.vi shows also the results obtained in the half dozen-ton industrial cast produced by VIM   +   VAR Melting   –   ingot Ø640 (VIM   +   VAR) as shown in Fig. 17.27:

Effigy 17.27. Industrial cast production steps [17].
•

Bar with diameter of 500   mm was forged.

•

Iv discs for welding trials were cut off and heat treated.

•

Remaining material was reforged to Ø300   mm and estrus treated.

•

Mechanical properties will be compared with rotor with the aforementioned diameter but forged from standard A263 in Saarschmiede.

17.11.1 Conclusions

Aubert & Duval has optimized C-263 grade based on these points:

•

higher microstructure stability regarding η phase

•

like workability and properties equally C-263

•

similar γ′ solvus temperature

•

similar γ′ content at 750°C

Trial and industrial tests were performed and demonstrated that chosen composition of optimized alloy satisfies the three criteria of material pattern.

17.eleven.ii Optimized alloy versus C-263

Microstructure:

•

after standard rut treatment: like grain size and same population of secondary γ′ precipitates,

•

after long-term crumbling: no η-phase precipitation after long-term aging.

Mechanical properties:

•

after standard oestrus treatment: similar properties; tensile properties could be improved with a better arrangement of Ti and Al contents,

•

afterwards long-term aging: no decrease of bear on strength and pitter-patter rupture life for optimized alloy.

The new composition seems promising for a new superalloy with high potential for applications at high temperature and long time in futurity A-USC steam turbines.

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Crack dynamics and fragmentation

Lili Wang , ... Xiquan Jiang , in Dynamics of Materials, 2019

9.1.nine.1 Loading technique

Early on studies on dynamic fracture toughness of materials used pendulum impact test (the then-called Charpy impact test) or drop-weight exam with notched specimens. It should be noted that such loading technology, on the one hand, is difficult to achieve loftier loading rate; on the other paw, more importantly, it is hard to quantitatively analyze the stress wave issue in the specimen and loading device. Therefore, it has gradually been eliminated by other more perfect loading technology (projectile impact, explosion, and electromagnetic loading) as shown in Table 9.6 (run across e.g., Ravi-Chandar, 2004), which take already covered in the previous sections of this chapter and in the previous chapters of this.

Table 9.half dozen. Range of loading rate 1000 ˙ I d ( t , a ˙ ) and crack initiation fourth dimension t f for different loading techniques.

Quasistatic loading Drib-weight Projectile impact Explosion Electromagnetic loading
Loading rate
1000 ˙ I d ( t , a ˙ ) , MPa·mone/ii·south−one 		1 104 ten4–xviii x5 10five
Time to fracture (μs) >106 ∼100 1–100 1–20 x–100

Recall Fig. 9.8 when discussing the dynamic scissure initiation toughness of materials, and Fig. 9.30 and Fig. 9.31 when discussing the dynamic crevice arrest toughness of materials; those results were obtained past Ravi-Chandar and Knauss (1984a) past using the electromagnetic loading technology with adjustable load aamplitude and elapsing. The principle of this electromagnetic loading technology is schematically illustrated in Fig. nine.36.

Figure ix.36. Principle of crack loaded past electromagnetic pressure pulse.

A flat copper strip is folded back on itself and the space between the two layers is filled with an insulating strip. This assembly is then introduced into the cleft of unmarried-border crack specimen (Fig. 9.36a). When a pulse electric current flows through the copper loop, each leg generates a magnetic field. The electric current vector in each leg interacts with the magnetic field of the other leg to produce an electromagnetic repulsion that forces the conductors apart. The two legs press upon the top and bottom surfaces of the cleft with a uniform pressure (Fig. 9.36b). The trapezoidal pulse duration tin be adapted inside the range of 150μs with a ascension time in nigh 25μs. The pressure on the crack surface can be adjusted in the range of one–20   MPa, and the loading rate is in the gild of Thousand ˙ I d ( t ) = x five MPa grand /s . The major advantages of electromagnetic loading are: (i) it provides expert repeatable loading that makes experiments like shooting fish in a barrel; (ii) the experiment has been finished before the stress moving ridge reflected from the specimen purlieus dorsum to the crack tip and tin be modeled as a pressurized semiinfinite crack in an unbounded medium, so that is easy to clarify. Moreover, the dynamic crack initiation toughness of the material (Fig. 9.8) and the dynamic crack abort toughness of the cloth (Fig. 9.xxx and Fig. 9.31) can exist carried out in the same experiment.

Projectile affect is a typical method to generate a high loading charge per unit. Retrieve the plate bear upon experiment discussed in Affiliate 4 "dynamic experimental report of land equation of solids under high pressure", in which a flyer launched by gas gun impacts onto a target (specimen), and recall the Hopkinson bar technique discussed in Chapter seven "dynamic experimental study of material distortion law", both belong to the projectile bear upon engineering list in Table 9.6. Different from the drib-weight technique which straight impacts specimen past falling mass, the projectile impact loading technique is essentially loaded past stress waves.

A typical example of the dynamic fracture toughness experiment of materials adopting plate affect technique is shown in Fig. 9.37 (Ravichandran and Clifton, 1989). The 4340 steel circular plate specimen with the thickness of h and a circumferential precrack across one-half of its cross-department is impacted at velocity v 0 by a flyer with the thickness of h/2 driven by a gas gun. An incident compressive trapezoidal pulse is first applied to the specimen (without effect on crack extension), and later reflected from the free surface of the specimen, a tensile pulse load required by the experiment is formed at the crevice of half thickness of the specimen. By varying v 0 and h, the load magnitude and duration (in the lodge of μs) tin can exist adjusted. After analyzing the particle velocity history on the back surface of the specimen measured by the light amplification by stimulated emission of radiation interferometer (VISAR), the dynamic stress intensity gene K I d ( t ) (in the lodge of 100 MPa·m1/2) can be obtained. The corresponding loading charge per unit K ˙ I d ( t ) achieved in these experiments is as high as 108  MPa·gane/ii s−1. Chiliad I d ( t ) first increases with time t and is proportional to t 1/two, which is consistent with the analytical solution as shown in Fig. 9.vi. After cleft initiation and propagation, 1000 I d ( t ) then decreases with time, every bit shown in Fig. 9.37B.

Effigy 9.37. Dynamic fracture toughness experiment for cracked plate specimen impacted by flyer.

 From Ravichandran G., Clifton R.J., 1989. Dynamic fracture under aeroplane wave loading. Int. J. Fract. 40, 157–201, Fig. 2, p.163, Fig. 15, p.182. Reprinted with permission of the publisher.

Hopkinson bar technique has been adopted to conduct experimental enquiry on dynamic fracture toughness of materials past more than and more researchers (e.g., Kalthoff, 1986; Jiang and Vecchio, 2009), which has go more and more pop and mature.

The Hopkinson bar experiment technique has already introduced in item in affiliate 7 of this book. Here, we focus on its awarding in the written report of dynamic fracture toughness of materials.

Costin et al. (1977) first used the Hopkinson bar principle to study the dynamic crack initiation toughness of materials, as schematically shown in Fig. 9.38. The specimen is a long round rod with a circumferential precrack. An explosive accuse is detonated at i end of the specimen, generating a tensile pulse applied on the specimen. Two strain gauges are mounted to both sides of the precrack of the long rod specimen. The measured incident waves, reflected waves, and transmitted moving ridge are used to determine the dynamic crack initiation toughness of the textile. Crack initiation occurs in the range of twenty–25μs, and the loading rate K ˙ I d ( t ) reaches ten6  MPa·10001/2·south−1. However, because the long rod specimen itself plays the role of both Hopkinson incident bar and transmission bar at the same fourth dimension, it consumes a lot of textile and requires high processing engineering science.

Figure 9.38. Circumferential precracked rod specimen subjected to a tensile pulse generated by an explosive charge.

In addition to direct apply the tensile stress wave loading to the precracked specimen, the specimen can also be loaded through the Hopkinson compressive bar. In such example, a tensile stress wave tin be generated by reflecting the incident compressive stress wave from the free surface of the short specimen (Stroppe et al., 1992), equally schematically shown in Fig. 9.39. It is assumed that the compressive wave first passing through the specimen has no effect on the crack. Some researchers (e.1000., Lee et al., 2002) added a gratuitous sleeve to the short-cracked specimen, which was fixed between the Hopkinson incident bar and the transmitting bar (come across Fig. 7.7 in Chapter 7), and then that the incident compressive wave in the incident bar propagates into the transmitted bar through the sleeve, while the tensile wave reflected at the free end of the transmitted bar then loads the cracked specimen.

Figure nine.39. Croaky specimen loaded by the reflected tensile pulse using Hopkinson pressure bar.

The to a higher place is to load the cracked specimen by tensile stress. On the other side, based on the dissever Hopkinson pressure bar (SHPB) experimental technique, researchers have also developed a variety of ways to use compressive stress wave to load cracked samples.

Fig. 9.40 schematically shows that a compact compression (CC) specimen is directly compressively loaded by compressive pulse in an SHPB apparatu-s (run into due east.g., Rittel et al., 1992).

Figure ix.40. Meaty compressed specimen loaded by compression pulse.

A wedge-loaded meaty tension specimen (WLCT specimen) is loaded by compressive pulse using an SHPB apparatus (see due east.g., Klepaczko, 1979), equally schematically illustrated in Fig. 9.41. The WLCT specimen is placed between the loading wedge and the transmitted bar.

Figure 9.41. WLCT specimen loaded by compression pulse.

The SHPB apparatus is too peculiarly suitable for dynamic iii-point angle exam to diverse cracked specimen by using pinch pulses, which is convenient for the measurement of dynamic fracture toughness of materials.

Fig. 9.42 schematically shows a single-edge cracked specimen loaded in the one-betoken bend (i   PB) mode by compression pulse propagating through the Hopkinson incident bar (run into e.k., Ruiz and Mines, 1985). If the single-edge croaky specimen and the loading mode are the same equally that of the usual Charpy test, it can be regarded as an improved Charpy exam that can accept into business relationship the stress wave effect and thus tin reliably determine the dynamic initiation toughness of materials (Weisbrod and Rittel, 2000).

Figure ix.42. Unmarried-edge cracked specimen loaded by compression pulse.

In addition to the one-point bend (one   Atomic number 82) examination mentioned above, researchers have as well developed a diverseness of dynamic experimental techniques for iii-betoken bend (3   Atomic number 82) specimens using Hopkinson pressure bar (Jiang and Vecchio, 2009) to study the dynamic fracture toughness of materials, as shown in Fig. nine.43 (meet eastward.thousand., Mines and Ruiz, 1985), Fig. nine.44 (see due east.one thousand., Jiang and Vecchio, 2007), and Fig. 9.45 (see east.g., Yokoyama and Kishida, 1989).

Figure 9.43. Three-point bend (3   PB) croaky specimen loaded past a single incident bar (1bar/iii   PB).

Figure 9.44. Three-point bend (3   PB) cracked specimen placed between the incident bar and the manual bar (2bar/3   Pb).

Figure 9.45. Three-indicate bend (3   PB) cracked specimen placed between the incident bar and double transmission bars (3bar/three   Pb).

Fig. 9.43 shows that compression pulse loading is direct practical to the three-bespeak bending crack sample past using a unmarried incident bar.

Fig. 9.44 shows that the pinch pulse loading is applied to the iii-point bending cracked specimens sandwiched between the incident bar and the transmission bar.

Fig. 9.45 shows that the three-indicate bending croaky specimen sandwiched between the incident bar and the double manual bar is subjected to compression pulse loading.

Mainly the Fashion-I cracked specimens are discussed above. Similarly, the Hopkinson pressure bar technique tin can besides be developed to report dynamic fracture toughness on Mode-Two croaky specimen. As shown in Fig. 9.46, Dong et al. (1998) adopted Hopkinson pressure bar apparatus to load a unmarried-edge parallel double-cracks specimen to report the interaction betwixt scissure initiation and adiabatic shear for Mode-II crack. In the test, the incident bar is arranged in contact with the specimen at the position between the parallel double cracks; a pinch pulse is transmitted to the specimen through the incident bar, resulting in a Mode-II fracture (see Chapter ten.ane.5 "Interaction between adiabatic shear bands and cracks").

Effigy 9.46. Experimental report on dynamic fracture toughness of Mode-2 crack by Hopkinson force per unit area bar (Dong et al., 1998).

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French Work on Fracture

D. Miannay , in Progress in Fracture Mechanics, 1983

B Dynamic Toughness

The initiation toughness under dynamic conditions is determined at medium speed with servohydraulic testing apparatus and with instrumented Charpy bear on tests by several organizations such equally the Institut de Recherche de la Sidérurgie, Creusot-Loire and the Commissariat à l'Energie Atomique, mainly for steels, irradiated or not. At high speed, a few organizations, the Commissariat à l'Energie Atomique, the Etablissement Technique Central de l'Armement and the Université de Metz, use the Hopkinson bar methodology. Then, initiation toughness is obtained over a big speed range.

In the crack-arrest toughness field, the Commissariat à fifty'Energie Atomique participated to the Electric Power Research Institute round-robin programme in which the dynamical propagation behavior or the static behavior at arrest were under investigation. At present, testing is currently done for steels.

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