Effect of Prestrain on Fracture Toughness of Rolled Mild Steel with Significant Inclusion Content

The basic method of JIc calculation using a single specimen is discussed. Dokouipil's approach for evaluating the JIc value is extended further and the effect of prestrain on rolled mild steel with significant inclusions is studied using this modified approach. Although this method does not give an accurate value of JIc, it is quite effective for a comparative study. While the fracture toughness of annealed and 7% prestrained materials are about the same, the fracture toughness of 3% prestrained material is significantly lower.

Experimental estimation of friction force in lubricated cutting of steel

Friction force generated in lubricated cutting of steel is experimentally estimated by recording the tangential force experienced by the spherical face of a pin rubbing against a freshly cut surface. The pin and the cutting tool are both submerged in the lubricant and the pin is situated on the cut-track to record the force. The recording shows an instantaneous achievement of a peak in the force curve followed by a decline in time to a steady state value. The peak and not the steady state friction was found to be sensitive to the structure of the hydrocarbon and addition of additive to the oil. The configuration was designed and tested to demonstrate the influence of a reaction film which develops during cutting, on cutting tool friction. Given the strong correlation between the peak friction and the existence of a tribofilm in the cutting zone, the configuration is used to determine the lower limit of a cutting speed regime, which marks the initiation of lubricant starvation, in cutting of steel using an emulsion as a cutting fluid. (C) 2010 Elsevier B.V. All rights reserved.

Koko kansan koti vai kommunistien pesäke? Helsingin Kulttuuritalon rakentaminen ja paikan henki 1955-1959

Helsingin Kulttuuritalo rakennettiin vuosina 1955–1958 vastaamaan Suomen kommunistisen puolueen ja muiden kansandemokraattisten järjestöjen toimitilojen puutteeseen. Kulttuuritalo oli myös kommunistien vastaus Helsingissä jo 1900-luvun alusta lähtien käytyyn konserttisali keskusteluun. Kulttuuritalo rakennettiin SKP:n päämajaksi, mutta sinne asettui myös lukuisia muita kansandemokraattisia järjestöjä. Kulttuuritalon suunnitteli professori Alvar Aalto. Pro gradu -tutkielmassani olen tarkastellut Helsingin Kulttuuritalon rakentamista ja paikan hengen muodostumista vuosien 1955–1959 välillä. Aikarajaus kattaa Kulttuuritalon rakennusvuodet sekä sen ensimmäisen kokonaisen toimintavuoden. Tutkielman ensisijaiset tutkimuskysymykset ovat: Miksi Helsingin Kulttuuritalo rakennettiin, millainen rakennusprosessi oli ja millainen paikan henki Kulttuuritalolle muodostui vuosien 1955–1959 aikana? Teoreettisen viitekehyksen tutkielmalle muodostaa paikan hengen käsite. Primäärilähteinä tutkielmassa ovat Kansan Arkistosta löytyvät Kulttuuritalo Oy:n ja Kulttuurityö ry:n kokoelmat sekä sanomalehdet. Sanomalehtiä käytetään Kulttuuritalon paikan hengen ilmentämiseen. Kulttuuritalo rakennettiin pääasiassa talkoovoimin. Talkoisiin osallistui runsaasti ihmisiä niin pääkaupunkiseudulta kuin ulkopaikkakunnilta. Suurin osa Kulttuuritalon rakentamisen rahoituksesta tuli kommunistisilta poliittisilta järjestöiltä ja ammattijärjestöiltä. Pyynnöistä huolimatta Helsingin kaupungilta tai Suomen valtiolta ei tippunut tukea kommunistien hankkeelle. NKP osallistui Kulttuuritalon rakennuskustannuksiin sekä suorin tavaralahjoituksia että epäsuoraan Bukarestissa sijainneen kansainvälisen rahaston kautta, joka toimi SKP:n rahoittajana. Kulttuuritalon paikan hengen luominen liittyi tiiviisti Kulttuuritalon rakentamiseen, sillä paikan henki alkoi muodostua jo talon rakennusvaiheessa. Kulttuuritalon paikan hengen rakentamiseen osallistuivat niin kommunistit ja kansandemokraatit kuin kommunismin vastustajat. Kommunismin vastustajilla tarkoitan tutkielmassa oikeistoa ja sosiaalidemokraatteja. Kommunismin vastustajat vastustivat tavallisesti myös Kulttuuritaloa, mikä kytkee 1950-luvun suomalaisen antikommunismin Kulttuuritalon paikan hengen muodostamiseen. Kun kommunistit rakensivat Kulttuuritalon paikan hengen positiivista puolta, sosiaalidemokraatit ja oikeistolaiset lehdet osallistuivat sen negatiivisen puolen muodostamiseen. Kulttuuritalon paikan hengestä muodostui vuosien 1955–1959 aikana voimakkaan punainen. Kulttuuritalon punaisuus sai kuitenkin kaksi merkitystä: Kommunisteille ja kansandemokraateille se merkitsi työväenliikkeen solidaarisuutta, tasa-arvoa ja voimaa. Kulttuuritalo oli heille osoitus työväen voimasta, ja he toivoivat sen auttavan kommunisteja saavuttamaan laajemman kannatuksen ja hyväksytyn aseman yhteiskunnassa. Kommunismin vastustajille Kulttuuritalo puolestaan merkitsi perinteistä yhteiskuntaa uhkaavaa tekijää. Kulttuuritalon oli heidän mielestään vaarallinen paikka, jonka avulla kommunistit pyrkivät vahvistamaan asemiaan yhteiskunnassa. Kulttuuritalon paikan henki heijasti näin suomalaisen yhteiskunnan kahtiajakautuneisuutta. Kulttuuritalon paikan henki vaikutti myös talon käyttöön. Kulttuuritalon ottivat innolla omakseen kommunistit ja kansandemokraatit, mutta sosiaalidemokraatit ja oikeistolaiset eivät halunneet sitä käyttää, vaikka Kulttuuritalon juhlasali olikin Helsingissä ainoa, joka täytti kansainvälisestikin tasokkaan akustiikan vaatimukset.

Comparative Study of Predictions of Flexural Strength of Steel Fiber Concrete

Several methods are available for predicting flexural strength of steel fiber concrete composites. In these methods, direct tensile strength, split cylinder strength, and cube strength are the basic engineering parameters that must be determined to predict the flexural strength of such composites. Various simplified forms of stress distribution are used in each method to formulate the prediction equations for flexural strength. In this paper, existing methods are reviewed and compared, and a modified empirical approach is developed to predict the flexural strength of fiber concrete composites. The direct tensile strength of the composite is used as the basic parameter in this approach. Stress distribution is established from the findings of flexural tests conducted as part of this investigation on fiber concrete prisms. A comparative study of the test values of an earlier investigation on fiber concrete slabs and the computed values from existing methods, including the one proposed, is presented.

Micromechanics Of Fatigue Crack-Growth At Low Stress Intensities In A High-Strength Steel

An attempt to systematically investigate the effects of microstructural parameters in influencing the resistance to fatigue crack growth (FCG) in the near-threshold region under three different temper levels has been made for a high strength low alloy steel to observe in general, widely different trends in the dependence of both the total threshold stress intensity range, DELTA-K(th) and the intrinsic or effective threshold stress intensity range, DELTA-K(eff-th) on the prior austenitic grain size (PAGS). While a low strain hardening microstructure obtained by tempering at high temperatures exhibited strong dependence of DELTA-K(th) on the PAGS by virtue of strong interactions of crack tip slip with the grain boundary, a high strength, high strain hardening microstructure as a result of tempering at low temperature exhibited a weak dependence. The lack of a systematic variation of the near-threshold parameters with respect to grain size in temper embrittled structures appears to be related to the wide variations in the amount of intergranular fracture near threshold. Crack closure, to some extent provides a basis on which the increases in DELTA-K(th) at larger grain sizes can be rationalised. This study, in addition, provides a wide perspective on the relative roles of slip behaviour embrittlement and environment that result in the different trends observed in the grain size dependence of near-threshold fatigue parameters, based on which the inconsistency in the results reported in the literature can be clearly understood. Assessment of fracture modes through extensive fractography revealed that prior austenitic grain boundaries are effective barriers to cyclic crack growth compared to martensitic packet boundaries, especially at low stress intensities. Fracture morphologies comprising of low energy flat transgranular fracture can occur close to threshold depending on the combinations of strain hardening behaviour, yield strength and embrittlement effects. A detailed consideration is given to the discussion of cyclic stress strain behaviour, embrittlement and environmental effects and the implications of these phenomena on the crack growth behaviour near threshold.

Stress-strain characteristics of Tress-strain characteristics of reinforcing steel bars under cyclic loading

This paper presents test results for 22 high strength deformed bars and nine mild steel bars subjected to monotonic repeated and reversed axial loading to determine the stress-strain behavior. Equations have been proposed for the stress-strain curves and have been compared with test results. Satisfactory agreement was obtained.

Stress-Strain Characteristics of Reinforcing Steel Bars Under Cyclic Loading

This paper presents test results for 22 high strength deformed bars and nine mild steel bars subjected to monotonic repeated and reversed axial loading to determine the stress-strain behavior. Equations have been proposed for the stress-strain curves and have been compared with test results. Satisfactory agreement was obtained.

A numerical study of projectile impact on mild steel armour plates

The present article deals with the development of a finite element modelling approach for the prediction of residual velocities of hard core ogival-nose projectiles following normal impact on mild steel target plates causing perforation. The impact velocities for the cases analysed are in the range 818–866.3 m/s. Assessment of finite element modelling and analysis includes a comprehensive mesh convergence study using shell elements for representing target plates and solid elements for jacketed projectiles with a copper sheath and a rigid core. Dynamic analyses were carried out with the explicit contact-impact LS-DYNA 970 solver. It has been shown that proper choice of element size and strain rate-based material modelling of target plate are crucial for obtaining test-based residual velocity.The present modelling procedure also leads to realistic representation of target plate failure and projectile sheath erosion during perforation, and confirms earlier observations that thermal effects are not significant for impact problems within the ordnance range. To the best of our knowledge, any aspect of projectile failure or degradation obtained in simulation has not been reported earlier in the literature. The validated simulation approach was applied to compute the ballistic limits and to study the effects of plate thickness and projectile diameter on residual velocity, and trends consistent with experimental data for similar situations were obtained.

A finite element analysis of dynamic fracture initiation by ductile failure mechanisms in a 4340 steel

In some recent dropweight impact experiments [5] with pre-notched bend specimens of 4340 steel, it was observed that considerable crack tunneling occurred in the interior of the specimen prior to gross fracture initiation on the free surfaces. The final failure of the side ligaments happened because of shear lip formation. The tunneled region is characterized by a flat, fibrous fracture surface. In this paper, the experiments of [5] (corresponding to 5 m/s impact speed) are analyzed using a plane strain, dynamic finite element procedure. The Gurson constitutive model that accounts for the ductile failure mechanisms of micro-void nucleation, growth and coalescence is employed. The time at which incipient failure was observed near the notch tip in this computation, and the value of the dynamic J-integral, J d, at this time, compare reasonably well with experiments. This investigation shows that J-controlled stress and deformation fields are established near the notch tip whenever J d , increases with time. Also, it is found that the evolution of micro-mechanical quantities near the notch root can be correlated with the time variation of J d .The strain rate and the adiabatic temperature rise experienced at the notch root are examined. Finally, spatial variations of stresses and deformations are analyzed in detail.

Criteria for prediction of flow instabilities and microstructural manifestations during warm working of AISI 304L stainless steel

The deformation characteristics of 304L stainless steel in compression in the temperature range 20–700°C and strain rate range 0·001–100 s−1 have been studied with the aim of characterising the .flow instabilities occurring in the microstructure. At higher temperatures and strain rates the stainless steel exhibits flow localisation, whereas at temperatures below 500°C and strain rates lower than 0·1 s−1 the flow instabilities are due to dynamic strain aging. Strain induced martensite formation is responsible for the flow instabilities at room temperature and low strain rates (0·01 s−1). In view of the occurrence of these instabilities, cold working is preferable to warm working to achieve dimensional tolerance and reproducible properties in the product. Among the different criteria tested to explain the occurrence of instabilities, the continuum criterion, developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all the above instability features.

Effect of microstructure and hardness on the grinding abrasive wear resistance of a ball bearing steel

Grinding media wear appears to be non-linear with the time of grinding in a laboratory-scale ball mill. The kinetics of wear can be expressed as a power law of the type w=atb, where the numerical constant a represents wear of a particular microstructure at time t = 1 min and b is the wear exponent which is independent of the particle size prevailing inside a ball mill at any instant of time of grinding. The wear exponent appears to be an indicator of the cutting wear mechanism in dry grinding: a plot of the inverse of the normalised wear exponent (Image ) versusHs (where Hs is the worn surface hardness of the media) yields a curve similar to that of a wear resistance plot obtained in the case of two-body sliding abrasive wear. This method of evaluating the cutting wear resistance of media is demonstrated by employing 15 different microstructures of AISI-SAE 52100 steel balls in dry grinding of quartz in a laboratory-scale ball mill.