Tip Defects Research Articles

Identification of the viscoplastic behavior of a polycarbonate based on experiments and numerical modeling of the nano-indentation test

Indentation testing is a convenient means to study mechanical properties of thin coatings. We suggest a new method to identify the viscoplastic behavior of a polymer by using the force-penetration curves during nano-indentation testing performed with two indenter shapes. During loading, the load applied by the indenter and the penetration depth have been measured. These force-penetration curves have been compared to the load computed by using the finite element method with a two dimensional software. The viscoplastic behavior of the polymer is modeled with the G'sell-Jonas law. The main particularity of this law is the modeling of the large strain-hardening at large strains. The unknown parameters of this law have been obtained by fitting computed and experimental force-penetration curves. We have identified each parameter independently of the others by taking into account the indenter tip defect. The nano-indentation tests have been performed with three strain rates and with two indenter shapes: a Berkovich indenter and a cone with a semi angle of θ = 30° and a tip radius. In this paper, the polymer is a polycarbonate. Several authors have made rheological tests on this polymer. The true strain-true stress curve obtained with our method is in good agreement with the compression curve.

The dorsal nasal flap revisited: aesthetic refinements in nasal reconstruction.

ECONSTRUCTING SURGICAL DEFECTS of the nasal tip and lower third of the nose presents a unique challenge for the facial plastic surgeon. Treatment options include: secondary intention healing, full- and splitthickness skin grafts, and local and distant flaps. Owing to the unique texture and color of nasal skin, it is always preferable that like tissue be replaced by like tissue. Scars are best placed at the junction of aesthetic units while reconstruction should adhere to nasal subunit principles. The work of Burget and Menick 1 raised the standard for nasal reconstruction; however, the popularized paramedian forehead flap is a distant flap with significant donor site morbidity and requires second-stage reconstruction. The dorsal nasal flap is a local flap that uses nasal skin for a single-stage reconstruction. It involves rotation advancement of dorsal nasal skin from the upper two thirds of the nose and glabella to the lower nose. The dorsal nasal flap is certainly not our original concept; this article is to support previous works, further demonstrate its usefulness and versatility, and describe detailed refinements to achieve improved and predictable aesthetic results.

Finger tip defect injuries

Finger tip defect injuries

Nanoindentation of Poly (Methyl Methacrylate)

ABSTRACTFor the indentation of an elastic-plastic homogeneous half-space with a pyramidal indenter, the load theoretically increases with the square of the total penetration depth. Experimental data are presented in the current paper that demonstrate the validity of this relationship for an organic polymer and a Berkovich indenter, provided that appropriate account is taken of the tip defect and viscoplasticity. It is also shown that a simple analytical solution exists for the ratio of the contact depth to the total penetration depth. These findings assist in identifying procedures for obtaining the rate-dependent mechanical properties of thin polymer coatings or polymeric materials with depth-dependent mechanical properties.

The Reverse Auricular Flap: A New Flap for Nose Reconstruction

In the present article, the authors describe a new chondrocutaneous island flap from the ear helix for nose reconstruction. Anatomic studies showed that helix vascularization depends mainly on the superficial temporal vessels. The presence of vascular communications between the anterior frontal branch of the superficial temporal system and the supraorbital and supratrochlear arterial systems allows this flap to be used in a reverse vascular flow fashion. This new flap has been used successfully in seven cases for reconstructing composite defects of the nasal tip and ala. The donor-site defect is repaired with an advancement and rotation flap from the helical rim, leaving an inconspicuous scar and giving an acceptable cosmetic result of the donor area.

Strain-rate effects on hardness of glassy polymers in the nanoscale range. Comparison between quasi-static and continuous stiffness measurements

Strain rate effects on Hardness and Young's modulus of two glassy polymers, poly(diethylene glycol bis allyl carbonate) (CR39) and bisphenol-A polycarbonate (PC), were studied in the nanoscale range. Before analyzing material behaviors, we focused on a particular phenomenon prevailing at the first stage of the contact between the surface of these polymers and the Berkovitch diamond tip used in the experiments, leading to an apparent increase of the tip defect (i.e., the missing tip of the diamond from having a shape equivalent to a perfect cone). The common methods based on calibration functions of the tip appear to be inaccurate to calculate correctly the contact area at the nanoscale range for these polymers. A new method based on Loubet et al.'s model to calculate the contact area by taking account of the apparent tip defect is proposed. The hardness values obtained this way were compared to the compressive yield stress using Tabor's relationship. A hardness-yield stress ratio close to 2.0, as expected on such polymers, was found. A strain-rate effect on the load-depth curve for these two polymers is interpreted as an increase of the hardness with the strain rate. The results from quasi-static and dynamic (the continuous stiffness method) measurements are compared. The strain-rate effect on Young's modulus in dynamic conditions should be taken into account in the hardness calculation.

Use of the Nasal SMAS to Reconstruct Defects of the Tip, Alae, Columella, or Septum

Use of the Nasal SMAS to Reconstruct Defects of the Tip, Alae, Columella, or Septum

Mechanical properties of poly(ethylene terephthalate) at the near surface from depth-sensing experiments

The viscoelastic-plastic properties of glassy poly(ethylene terephthalate) in the micron and submicron range have been investigated by means of load displacement analysis from depth-sensing experiments. Experimental data have been modelled using two methods: firstly assuming the elastic behaviour during initial unloading to be that of a cylindrical punch; secondly using a power-law relation. The creep behaviour under the indenter has been examined. Furthermore, the influence of the maximum penetration depth and loading and holding times on the hardness values are discussed. Hardness data from the depth-sensing and imaging methods are shown to be in good agreement. When using the depth-sensing method, hardness values are shown to be constant with decreasing penetration depth (0.5 μm ≤ h ≤ 9 μm), provided that a correction procedure to account for the indenter tip defect is applied. Young's modulus derived from the compliance method has been studied and results are discussed in the light of the various testing conditions employed.

Mechanical properties of poly(ethylene terephthalate) at the near surface from depth-sensing experiments

Abstract The viscoelastic-plastic properties of glassy poly(ethylene terephthalate) in the micron and submicron range have been investigated by means of load-displacement analysis from depth-sensing experiments. Experimental data have been modelled using two methods: firstly assuming the elastic behaviour during initial unloading to be that of a cylindrical punch; secondly using a power-law relation. The creep behaviour under the indenter has been examined. Furthermore, the influence of the maximum penetration depth and loading and holding times on the hardness values are discussed. Hardness data from the depth-sensing and imaging methods are shown to be in good agreement. When using the depth-sensing method, hardness values are shown to be constant with decreasing penetration depth (0.5 μm  h max  9 μm), provided that a correction procedure to account for the indenter tip defect is applied. Young's modulus derived from the compliance method has been studied and results are discussed in the light of the various testing conditions employed.

Pinch modification of the linear advancement flap for reconstruction of central nasal tip defects

Pinch modification of the linear advancement flap for reconstruction of central nasal tip defects

Surgical treatment of defects on the tip of the nose.

Malignant tumors frequently occur on the tip of the nose and may represent considerable therapeutic challenges. Dermatologic surgical approaches are outlined to achieve maximum cure rates with optimal cosmesis. Different excision techniques are shown to remove basal and squamous cell carcinomas as well as other malignant lesions on the tip of the nose. All operations can be performed under local anesthesia in a dermatologic surgical setting. Excisions with direct wound closure are sufficient for small tumors and may even enhance the appearance off the nose. Large tumors may require full-thickness skin grafts after extensive removal yielding acceptable cosmetic results. Multiple different local flaps are available for medium sized defects whereas large wounds including the nasal skeleton require loco-regional flap repair. Selection of the best defect repair allows the majority of nasal tip defects to be repaired with excellent functional and cosmetic results.

The two-stage nasolabial flap for subunit reconstruction of the ala

The nose can be divided into subunits: the dorsum, tip, columella, paired alae, sidewalls, and soft triangles. The alar subunit is a round, full hemisphere bounded by the alar groove, which separates it from the tip, cheek, and lip and by the shallow depression of the soft triangle. A modest excess of skin and subcutaneous fat is available in the nasolabial fold for reconstruction of alar defects. A nasolabial flap can provide ideal tissue to reconstruct defects of the ala, although it is insufficient in size and reach to cover the tip, dorsum, or large unilateral defects. If a fastidious patient wishes restoration of a significant alar defect to a near-normal appearance, a two-stage nasolabial flap is the primary choice. First, residual normal skin within the alar subunit is discarded, and the entire subunit is resurfaced. The alar defect is not patched. Then, a superiorly based nasolabial flap based on axial perforators from the underlying facial musculature is designed based on a pattern of the contralateral normal ala. Alar support is provided by a primary cartilage graft which helps create an alar shape and braces the reconstruction against gravity and wound contraction. Aggressive subcutaneous thinning and soft tissue sculpturing can permit restoration of subtle contours in two stages, 3 weeks apart.

Reconstruction of Nasal Tip Defects by Dorsonasal V-Y Advancement Island Flap

The nasalis musculocutaneous sliding flap developed by Rybka and the myocutaneous axial flap with lateral pedicle reported by Martire and associates are extremely useful for reconstruction of the nasal tip and surrounding area, respectively. We have modified the method of Martire and associates into an operative procedure that can be easily employed. By confirming the blood flow of the lateral nasal artery preoperatively by Doppler probing, the lateral pedicle of the flap was made smaller to facilitate mobilization of the flap. Furthermore, this flap could be made into a reversed-flow flap when indicated.

Rotation flaps to reconstruct nasal tip defects following Mohs surgery.

Skin cancer involving the nasal tip is fairly common. The repair of these nasal tip defects is often a challenging opportunity. The current range of reconstructive techniques include partial closure and second intention healing to skin grafts and midline forehead flaps. Here we present an interesting method of nasal tip repair harvesting a rotation flap that uses adjacent skin from lateral and upper bridge of nose. Using three case studies examples of the rotation flap are demonstrated to reconstruct the nasal tip defects following Mohs surgery for skin cancer. For medium size defects of up to 1 cm in diameter, rotation flaps offer an alternative surgical one-stage method of reconstruction of the nasal tip in selected cases. Satisfactory results can often be achieved with a modest amount of planning, intra-, and postoperative care. Rotation flaps possess a circular configuration that allow recapitulation of the natural creases and contours of nasal tip anatomy resulting in aesthetic repairs.

Twin tip defects related to the nucleation and growth mechanisms of the twin (1012) in zinc characterized by high-resolution electron microscopy

Abstract In order to determine the mechanisms of twin growth, a high-resolution electron microscopy study of the tip morphology in (1012) twin in zinc has been carried out. In a new model presented here, the twin tip is described as a series of (1012)//(1012) step faces, containing one or more interfacial dislocations. They are separated by incoherent (0001)//(1010) interfaces resulting from a pile-up of twinning dislocations. The stress around the twin tip is accommodated through the emission of (c + a)⅓ 〈1123〉 lattice dislocations and formation of residual dislocations b D ≈ 0·47[1011] which are of the opposite sign to the twinning dislocation. This relaxation process can be associated with a blunting mechanism which finally stops the twin growth along the [1011] direction.

The chondrocutaneous ear helical free flap for the reconstruction of the defects of the nasal tip, columella and/or ala

Reconstruction of the full-thickness defect of the tip of nose, columella, and ala has always been a challenge. Local flaps can be used, but this often results in a bulky nose with an unsatisfactory aesthetic appearance requiring secondary surgical procedures. The use of the ear as a donor site for a microvascular free flap, although not general consensus despite structural similarities between the nose and ear, offers a possibility of a good reconstruction for such patients. Five patients presented with composite tissue defects of the tip, columella and ala of the nose resulting from human bites. Reconstruction was performed early in order to avoid possible infection. The free flap was designed and elevated from the upper part of the helix and concha of the opposite ear; the flap matched the traumatic defect on the nose and was based on the anterior auricular branches of the superficial temporal vessels. The free flap was brought to the defect and sutured to the margins. Direct end-to-end anastomosis of both vessels was performed in four patients while a venous grafts was needed in one patient. The donor flap area was closed directly. The follow-up period ranged from six months to five years. The reconstruction was satisfactory as to contour, symmetry and colour match in four patients. The final aesthetic result was obtained by touch-up procedures under local anesthesia. The donor site deformity was minimal. In one patient, the free flap was lost due to venous thrombosis and late reintervention. The chondrocutaneous free flap represents a dependable vascularized composite tissue transfer that offers a straightforward one-stage reconstruction of tissue defects of the tip, columella, and ala of the nose. The additional advantages of freedom in the flap design and structural similarity between the nose and ear makes it an ideal choice for such defects.

The elastoplastic response of poly(methyl methacrylate) to indentation

This paper describes an experimental and analytical study of the contact compliance and hardness of a glassy polymer, poly (methyl methacrylate), which has an elastoplastic response to indentation using rigid conical and spherical indenters. The experimental method and the associated intrinsic errors are described. The nature and importance of these errors are reviewed and a variety of corrections are applied. The potential errors addressed include the zero error, the indenter tip defect correction and the problems associated with various extrapolations and interpolations of the experimental data necessary in order to abstract the material characteristics of the polymer. The analytical description of the data has been facilitated by an adaptation of the Box-Cox transformation (Box, G. E. P. Sz Cox, D. R. 1964 J. R. Statist. Soc. 26, 211), which is shown to be a most effective way of abstracting the required material characteristics data and minimizing the influence of the intrinsic errors inherent in the compliance method. The deduced material response characteristics of the polymer, in particular the Young’s modulus and the yield stress, are shown to be consistent with data obtained by conventional mechanical testing methods.

Application of the compliance method to microhardness measurements of organic polymers

Abstract This paper presents an experimental and analytical study of the contact compliance and hardness of a number of organic polymers. The force–displacement data are used in conjunction with the indenter tip defect correction and a curve-fitting procedure to obtain the microhardness and Young's moduli values of the polymers. These microhardness values, obtained from the compliance method, are compared with similar results from the conventional imaging technique and it is shown that the compliance method is an effective means of evaluating the hardness of polymers. The effect of water as plasticizer on the surface mechanical properties of a nylon is also investigated using this technique.

Improvements in the indentation method with a surface force apparatus

Abstract On the nanometre scale, the actual indenter-material contact area must be carefully determined to obtain reliable values of mechanical properties from an indentation test. On this scale, the contact area is greatly affected by the geometrical tip defect and by the possible formation of plastic pile-up (or sink-in) around the indent. Parameters such as local surface roughness and heterogeneity in surface and in thickness make it di5dt to conduct and to interpret nanoindentation tests. A new method, which couples nanoindentation experiments and imaging procedures, has been developed. Nanoindentation tests and topographic images are performed with a surface force apparatus developed in our laboratory. The important point of our method is the ability of our three-axis device to generate topographic images without having to move the sample. This allows us to determine precisely the actual tip–sample contact area, while performing accurate continuous quantitative quasistatic load measurement and simultaneous dynamic measurement of the contact stiffness against penetration depth. In this paper, the method is described. Results obtained on a gold layer are presented as an illustration of the method. They show how we solve some problems and try to push forward the limits of indentation tests.

Conchal bowl skin grafting in nasal tip reconstruction: Clinical and histologic evaluation

Background: It is often difficult to achieve an esthetically pleasing cosmetic match when full-thickness skin grafts from periclavicular, preauricular, or postauricular donor sites are used to repair distal nasal defects. This, in large part, is due to the highly sebaceous nature of the skin on the distal aspect of the nose. Objective: Our purpose was to describe the benefits of using donor skin from the conchal bowl to repair defects of the nasal tip. Methods: The technique of conchal bowl grafting is described. Results: The conchal grafts give an excellent cosmetic result with respect to color and texture match and are time efficient because the donor site can be allowed to heal by secondary intention. Conclusion: The conchal bowl offers an esthetically reliable source of donor skin for full-thickness and perichondrial cutaneous grafts to repair defects of the nasal tip.