Time-dependent craze zone growth at a crack tip in polymer solids

Luo, Wenbo; Yang, Ting–Qing; Wang, Xiayu

doi:10.1016/j.polymer.2004.03.014

Cited by 22 publications

(8 citation statements)

References 12 publications

(9 reference statements)

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“…In these cases, the mechanism of crazing enables polymers to absorb energy through the matrix (in-elastic) deformation. This is possible because the energy used to initiate crazing, and crack growth is large and allows the energy to be dissipated over a large area (Luo et al 2004;Topoleski et al 1990). Alternatively, in thermosetting plastics, crazing may lower the strength of the polymer and lead to premature failure (Scheirs 2000b).…”

Section: Fatigue Crack Growthmentioning

confidence: 99%

MWCNT Used in Orthopaedic Bone Cements

Dunne¹,

Ormsby²

2011

Carbon Nanotubes - Growth and Applications

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implant procedures. In 2005, cement was used for the fixation of 73% of femoral stems and 53% of acetabular cups, in England and Wales (NJR 2006). 2.3 Acrylic bone cement Poly (methylmethacrylate) (PMMA) has been used in orthopaedics since the early 1960s (Charnley 1960). It was first introduced by Sir John Charnley and Dr Dennis Smith. Also known as acrylic bone cement, it acts as a grouting agent for the fixation of artificial joints as well as the treatment of spinal compression fractures (vertebroplasty). In TJR, bone cement fills the space between prosthesis and bone and acts as an elastic buffer, therefore transferring mechanical load on the implant to the bone. This function of distributing stresses is critical for implant longevity. If the external stresses exceed the ability of the cement to transfer the load, a fracture results (Kuehn et al., 2005). Acrylic bone cement is a two phase system, consisting of a polymer powder and monomer liquid. The powder phase primarily consists of spherical PMMA beads (82-89 wt. %), in addition to an inorganic radiopacifying agent, usually barium sulphate or zirconium dioxide (10-15 wt. %). The powder component also contains benzoyl peroxide (BPO; 0.5-2.6 wt. %), which catalyses polymerisation. The liquid phase is largely MMA monomer (98 wt. %), with 2 wt. % N, N-Dimethyl-p-toluidene (DmpT) which accelerates the polymerisation. From a chemical point of view, MMA is an ester of methacrylic acid with a polymerisable double bond. When the liquid and powder phases are mixed, the initiator (BPO) reacts with the accelerator (DmpT) to form free radicals in what is known as the 'initiation reaction'. These free radicals initiate polymerisation of MMA into PMMA by adding to the polymerisable double-bond of the monomer molecule. Temperatures during this reaction can reach up to 110ºC. During polymerisation, the bone cement is worked into a 'dough' phase that can be moulded or injected. In a relatively short amount of time (10-15 minutes) the bone cement hardens to ca. 90% of its final mechanical properties (Kuehn et al., 2005). Although current revision rates of cemented TJR are low, improved mechanical and thermal properties are required to further reduce subsequent surgeries of cemented arthroplasties, and increase the longevity of the implant. With 88.7% of current cemented implants expected to last at least 14 years (Karrholm et al. 2008), this would mean that more physically active patients would have to undergo a number of revision surgeries in their lifetime. Furthermore, younger patient populations are more likely to impose heavier, more complex loadings on the implant, as they would wish to continue pursuing an active lifestyle. 3. Composition and polymerisation reaction 3.1 Composition Acrylic bone cement, as mentioned is primarily composed of poly methylmethacrylate (PMMA). Most commercial acrylic bone cements comprise of a two part self-curing acrylic polymer, usually formulated as a 2:1 powder to liquid ratio. These components are mixed immediately prior to implantati...

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Section: Fatigue Crack Growthmentioning

confidence: 99%

MWCNT Used in Orthopaedic Bone Cements

Dunne¹,

Ormsby²

2011

Carbon Nanotubes - Growth and Applications

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“…However, the craze fraction assessed by the above protocol overestimates the actual void fraction in the deformed material since it includes unduly the solid space occupied by the microfibrils that were present before their elimination by the chemical attack. According to several authors [40][41][42][43], the volume fraction of micro-fibrils in the crazes represents about 40% for most polymers. Therefore, the actual void fraction within an exposed section should be estimated by f vr Z0.6!…”

Section: Microstructural Investigationmentioning

confidence: 99%

Characterization of volume strain at large deformation under uniaxial tension in high-density polyethylene

Addiego

Dahoun

G’Sell

et al. 2006

Polymer

150

140

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“…The mode of yielding is a dilatational process via the formation of crazes. The craze is a localized plastic zone that develops above a critical stress level, giving rise by cavitation to a local dilatation via void creation of oriented fibrils which break at sufficiently high stress accelerating the cracking …”

Section: Introductionmentioning

confidence: 99%

Highlighting delayed elastic processes at zero stress in a polymer glass

Mbarek

Baroni

Noirez

2015

Polymer International

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International audienceThe present study highlights the existence of a post-evolution of the fracture and damage in glassy polymers at zero-stress relaxation evidencing that the dynamic is not frozen below the glass transition but that it releases at zero stress in the plastic regime from past stresses. The observation of a further evolution of the glass without applied stress (at zero stress) is unexpected and inaccessible using conventional tensile tests since they are not designed to enable a zero-stress measurement. Non-contact methods such as confocal microscopy and autocorrelation analysis are used to examine polymethylmethacrylate samples plastically deformed (up to 8% elongation rate) and subsequently studied in the unloaded state. The zero-stress evolution is morphologically characterized by a nucleation of new microfractures and an evolution of the existing cracking. The analysis of the image correlation indicates that the strain field continues to evolve revealing an intermittent retraction of the displacement field at time scales up to several days. Different temperatures from −75 °C up to −45 °C below the glass transition have been tested and prove that the retraction process is thermally activated. The retraction process (about 1% − 2% of the deformation rate) implies that plastic deformation does not relax completely from anterior stresses but exhibits a delayed elasticity. These properties have profound consequences impacting the future physical and mechanical properties of the material

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Time-dependent craze zone growth at a crack tip in polymer solids

Cited by 22 publications

References 12 publications

MWCNT Used in Orthopaedic Bone Cements

MWCNT Used in Orthopaedic Bone Cements

Characterization of volume strain at large deformation under uniaxial tension in high-density polyethylene

Highlighting delayed elastic processes at zero stress in a polymer glass

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